Exocortis is a virus-like disease of citrus tree bark. I say virus-like because it is caused by a particle, not a virus, called the Citrus Exocortis viroid (CEVd).
Viroids are the smallest known infectious pathogens, made up of a single, naked strand of RNA. Other diseases caused by viroids include potato tuber spindle disease, avocado sunblotch, and peach latent mosaic.
For one thing, you may also see gum droplets under the loose bark, or stunting. Stunting occurs because nutrients are having a difficult time moving through damaged or exposed vascular bundles. Sunburn damage generally does not cause stunting or gummosis.
Dealing with exocortis
You can’t cure exocortis and it is highly contagious. That being said, it probably won’t kill your tree. What it will do is reduce production and make your tree susceptible to other pest and disease problems. Unless you are ready to commit to complete sanitation of shoes, tools, and anything else that might come into contact with an infected tree, its removal is your best option, if only to protect neighboring trees.
Imagine a container plant that grows a lush 6 feet tall and produces delicious, soft-skinned, seedless tropical fruits. Introducing… the babaco tree.
Also known as mountain papaya, babaco is cousin to that other sweet tropical fruit of mammoth size. Commonly eaten fresh, or used in fruit salads, smoothies, and ice cream, babaco (Carica pentagona Heilborn) is believed to be a naturally occurring hybrid from Ecuador. People have been eating babaco fruit since the 1500s, but I had never heard of it until recently.
These herbaceous shrubs feature thick, mostly unbranched trunks that are covered with leaf scars, similar to other members of the Carica genus. The healthier the plant, the thicker the trunk. Large, palmate leaves, with prominent veins and long petioles, make this an attractive house or patio plant. Flowers are all female and fruit is generated parthenocarpically. That’s a big word which means without seeds. And it’s the fruit that should make babaco worth considering for those of us who prefer growing our own food. Five-sided babaco fruit is large, reaching 12” in length and 8” wide. Said to taste like a combination of strawberry, papaya, and pineapple, the fruit is somewhat acidic and not overly sweet. The skin is also edible.
How babaco grows
Babaco performs best in cool subtropical climates. Too much sun exposure can result in sunburned fruit and immature fruit drop. While it prefers coastal areas, babaco can be grown it semi-protected areas throughout California and other Mediterranean regions. While babaco can withstand brief exposure to freezing temperatures (>28°F), they are best brought indoors or put in a protected place during the coldest part of winter to avoid root rot. Babaco plants can easily be grown in containers and they thrive in greenhouses (or warm, moist homes).
How to grow babaco
Since babaco do not produce seeds, they are propagated vegetatively, or asexually. To do this, one foot diagonal segments are taken from an existing trunk, after fruit production is completed. These segments are first washed with a fungicide and then the bottom (rooting) side is dipped in rooting hormone. Segments are then stored vertically in a location where they can dry out and form calluses, much the way we treat pineapples. In time, roots and shoots will begin to appear and the segment of trunk is planted 8” below soil level. In just a little over a year, your babaco will be producing fruit!
For the best fruit production, prune out any additional trunks as soon as they appear, except for one trunk, sometime around September, every year or two. This new trunk will replace the existing trunk. Trunks are only productive for a year or two. Babaco can also be propagated from cuttings, but with less success.
Babaco grows best in light, well-drained soil. They require frequent irrigation and nitrogen feeding during fruit production. Mulching with composted chicken bedding will help your babaco tree thrive.
Pests and diseases of babaco
Babaco leaves are susceptible to fungal diseases, such as powdery mildew. Phytophthora root rot can also become a problem. Certain mites, specifically the two spotted mite and the strawberry mite can become problematic, as can snails and slugs, and deer.
Add a touch of the tropics to your home or patio with a delicious babaco!
In many gardening catalogs, you can find trees that boast multiple types of fruit. This is done by grafting twigs from various trees onto a parent tree.
A man named Sam Van Aken created a tree with 40 different types of fruit growing on it. His Tree of 40 includes almonds, cherries, nectarines, peaches, and many other stone fruits, all grafted onto a single tree. Grafting is an excellent way of making the most out of a small gardening space and it can look pretty amazing. Grafting is an old technique used to join two plants together. A newer version, called budding, does the same thing, but in a different way.
How does grafting work?
The top half of a graft is called the scion and the lower portion is called the rootstock. Grafting works because plant hormones, called auxins, allow the vascular cambium tissues of both the scion and rootstock to merge. This allows water and sap to continue moving through the xylem and phloem.
Before you jump on the grafting bandwagon, however, keep in mind that grafting is tricky. It takes practice. You also need to know that, after a graft is completed, even though a protective callus has formed, and the vascular tissues have fused, the wood does not. This means that graft unions should always be considered structurally weak. You should also know that the fruit and nuts produced on grafted trees contain seeds that hold the genetic information for the scion wood only, and not that of the rootstock. Also, if you have a plant that is putting out suckers, keep in mind that these are from the root stock, and not the productive aboveground portion of your plant.
Advantages of grafting
It is pretty safe to assume that nearly all fruit and nut trees available today are grafted combinations of hardy, pest- and disease-resistant rootstock and highly productive scions.
Grafting speeds up production because young scions can be grafted onto older rootstock. This is called precocity and it allows growers to skip the 5- to 12-year juvenile phase, when trees are focusing on root system development, rather than fruit production. Grafted trees can also selected for size. Simply graft a scion from a full-sized tree onto dwarf rootstock and you get a dwarfed tree that produces more fruit. In many cases, grafting is used to imbue a tree with pest or disease resistance. This method is also used on watermelon, tomato, eggplant, cucumber, and other vegetative plants for the same reason.
Grafting for the garden
Let me say this up front - grafting requires skill. It easy to do incorrectly. There are several factors that contribute to successful grafts, and all of them are important:
Tools used in grafting
Having your tools ready ahead of time will increase your odds of successful grafting. The last thing you want is for plant tissue to dry out before you are done. [Many gardeners hold scions in their mouth as they work, to keep the plant tissue moist.] You will need sharp, sanitized pruning clippers, stretchable, biodegradable grafting tape, a sharp grafting knife, and sanitizer. You may also want to have some tree sealant or grafting wax handy.
Steps of T-budding: (a) Bud stick with short leaf stems. (b) Shield bud. (c) Inverted “T” and standard “T” cut in stock. (d) Bark opened and ready for bud. (e) Bud inserted and flaps closed. (f) Bud inserted for inverted “T” budding. (g) Rubber budding strip holding flaps and bud firmly in place. (UKY Extension)
Chip budding is similar to T-budding, except that a chip of wood is removed from the rootstock and the bud is inserted into the space.
There are several different types of grafts:
Approach grafting joins two rooted plants together to provide more support for the developing new growth. It is also used in pleaching and can be done any time of year.
Awl grafts are hard to do well as it means poking an awl under the bark of rootstock, but not beyond the cambium layer, and inserting the scion.
Bridge grafting is used in an attempt to save a tree that has been girdled by planting identical species around the injured tree and grafting them above the injury to create a nutrient bridge over the girdled portion of trunk. A similar method, called inarch grafting, uses an existing branch of the injured tree that emerges below to injury to reconnect the supply chain of nutrients.
Cleft grafting is one of the simplest and most popular forms of grafting. It takes advantages of naturally occurring clefts by inserting 3/8” scions into larger (3/4” to 2-3/4”) notches cut into Y or V-shaped joints while both plants are still dormant.
Four-flap grafts (or banana grafts) are a complex method of grafting, commonly used on pecans, in which bark from the rootstock is peeled back, like a banana, and applied to the scion.
Stub grafting is similar to cleft grafting, but the incision is made in a branch, instead of a cleft, and the scion is placed at an angle no more than 35° to the parent tree. After the scion takes, the portion of the branch above the graft is removed
In rare cases, graft hybrids, called chimera, will occur. This happens when rootstock tissues grow into the scion wood. This can lead to trees that produce flowers of both plants, plus strange combination flowers. Chimera are almost impossible to reproduce.
Whichever method you decide to use, grafting or budding, be sure to seal the area completely, either with grafting tape, tree seal, or grafting wax. This will protect against desiccation, pests, and disease, while providing some structural support, as well.
Problems associated with grafting
Grafting can provide you with added control over plants, making them more suitable to your garden theme. It can also make your foodscape healthier and more productive. But grafting requires skill and is labor intensive. Also, it is important that the proper rootstock is selected for your scions. Incompatibility may not kill the tree until several years of watering, fertilizing, and pruning have passed. Check with your local County Extension Office or rare fruit growers club for more information on compatibility before you get started.
When you first try your hand at grafting, don’t be surprised or discouraged when the alignment and pressure are insufficient, or the graft union dries out before the scion “takes” to the rootstock. This happens to beginners all the time.
If your graft works, make sure you plant your new tree at the proper planting depth. This is critical to its health and longevity. Placing graft unions below soil level invites fungal diseases, such as crown rot.
The interaction between rootstock and scion wood can be pretty amazing when it comes to plant hormones. Check out my post on photoperiodism.
Assuming you have already collected, labeled, and kept scions cool and moist, you are now ready to begin. [If not, read my post on scions first.]
Did you know that you can graft a tomato plant onto a potato plant and get food from both?
Now you know.
You may love calico cats (I do!), or have fond memories of calico dresses from a certain prairie-crossing children’s series, but calico in the plant world is something else entirely.
Calico is a viral disease that can infect alfalfa, lentils, potatoes, tomatoes, peas, tobacco, and 600 or so other plants. There are several strains of this virus, most of which are species dependent.
The calico virus prefers warm, sunny days and sap with a slightly alkaline pH of 7–7.5. Research has shown that plants infected with calico causes reduced levels of important plant nutrients such as copper, iron, manganese, and zinc.
Symptoms of calico
Calico, also known as Lucerne mosaic, or alfalfa mosaic virus (AMV), is easy to spot. Clearly visible in dark green sea of potato plants, you will see a bright yellow patch, or yellow blotching. Infected leaves may look shiny, compared to their healthy neighbors. You may also see wilting or severe stunting. Closer inspection will show dead stems and tubers, or dry, corky areas inside your potato harvest.
If your potato plant looks more like a pale yellow Christmas tree, it is probably potato psyllid feeding.
How calico is spread
Calico is spread by several species of aphid, but potato aphids and green peach aphids are the usual culprits. Infection is normally spread when aphids move from alfalfa, clover, or wheat to potato plants. Infected seeds and pollen can also carry this viral disease, as can parasitic dodder. Infected plants should be removed and tossed in the trash, not the compost pile.
To avoid AMV in your potato patch, plant only certified disease-free tubers, keep your potatoes away from clover and alfalfa, and sanitize your tools regularly.
A break in the much appreciated rain and I found myself out in the garden. [Where else?] When I moved a large plant container, I saw something I had never seen before.
Curled up in a perfect spiral, under what had been the very center of my container, I saw a flat yellow worm with a dark stripe down the middle of its back. Of course, I had to collect it for identification. Unfortunately, this particular specimen escaped and is, I believe, lodged in my moisture meter.
Land planarians, also known as land flatworms, or arrowhead flatworms, are a family of flatworms known as Geoplanidae. There are nearly 1,000 different species of flatworm worldwide, broken down into 4 subfamilies, but we know very little about them. What we do know is simply too strange not to share.
Land planarians are native to Indo-China. Sometime around 1901, soil containing these flatworms was transported to the U.S. At first, land planarians were only found in greenhouses. Now they are found in several states including: Alabama, California, Mississippi, New Jersey, New York, North Carolina, Ohio, Oklahoma, South Carolina, Tennessee, and Texas. If you find one in a state not listed, I’m sure that your local County Extension Office would love to see it. At this point, land planarians are only found in places where nursery plants go. They withstand freezing temperatures by hiding in protected areas. They cannot, however, tolerate low humidity or drought.
Land planarian description
Land planarians are flat, slimy worms. Apparently, the slime helps them move and is the only way they can maintain internal moisture levels. That slime is said to taste terrible, though I don’t know how or who figured that out. That bad taste means they have few, if any, natural predators.
Planarians can range from less than one inch to nearly a foot in length. Most planarian species tend to be brown or brownish-grey, but they can also be yellow, green, black, or even bluish-green. Most planarian species have dark longitudinal lines that start at the head. Heads tend to be triangular or crescent shaped. Planarians do not have a mouth, per se. Instead, they have a single opening on the underside of their body.
If the outside of a planarian looks strange, the inside is even more bizarre. Planarians are a mass of squishy tissue and nerves, with a layer of locomotive hairs on the underside. They have no brain, circulatory system, respiratory system, or digestive system. So, how do they eat?
Land planarian feeding
Cousin to parasitic tapeworms, planarians are nocturnal predators that feed on slugs and snails, pillbugs, millipedes, spiders, and earthworms. They use chemical signals that are produced in folds of their skin to detect prey. Some land planarians use physical force to hold their prey, while others have a sticky mucous that entraps their victim.
Now, when I said they feed, it isn’t feeding as we know it. When a land planarian feeds, it slimes over top of a potential food, attaches its “mouth” opening, and vomits digestive juices , liquifying its prey. Then, it sucks up the soupy nutrients. Land planarians do not have an anus, so waste products are released through the same opening used to bring it in. If that wasn’t weird enough, land planarian reproduction is even more odd.
Like many other flatworms, land planarians are able to reproduce either sexually or asexually. Sexual reproduction culminates in eggs being placed in cocoons that hatch in 3 weeks. A single planarian will, every couple of weeks or so, attach its tail to a rock or some other immoveable object and slime away, tearing its tail from its torso. A new tail grows from the wound, as we would expect of a flatworm. The tail segment left behind, however, does the same thing, growing a new torso and head within 10 days. [When food is scarce, it is not uncommon for land planarians to eat their own reproductive tissues.] Scientists love studying flatworms because of those reproductive habits. In one study, it was found that decapitated flatworms retained the memories of their parent worms. [I can’t make this stuff up.]
As far as invasive pests go, planarians are not a significant problem, unless you have a greenhouse or practice vermiculture. [Vermiculture refers to raising worms.] In most outdoor gardens, fluctuations in humidity help keep land planarian populations in check. If you do have a greenhouse, or raise worms, flatworms can wipe out your entire worm population in short order.
The next time you see slime trails, don't assume they were made by snails or slugs. It may be that those garden pests are on the run from something far more terrifying (to them).
Manganese is a micronutrient used by plants to make chlorophyll. Manganese can also be phytotoxic, which means it can be poisonous to plants.
Made by large stars just before they go supernova, manganese is the 12th most abundant element of the Earth’s crust, and early man used manganese as a pigment in cave paintings some 20,000 years ago. How we use it in the garden can help or harm our plants.
You may have heard about the nitrogen cycle, the Calvin cycle, or the carbon cycle, but did you know there is a manganese cycle? I didn’t either. It ends up that manganese can take many different forms, depending on what it is attached to. [Mg2+ is the form most commonly used by plants.]
Unlike many other elements, which can exist on their own in nature, manganese prefers being attached to other minerals, usually iron. This can cause a whole Domino Effect when it comes to feeding your plants. According to studies conducted by Cornell University, high levels of copper (Cu), iron (Fe), nickel (Ni), and zinc (Zn) can make it difficult for plants to absorb manganese. At the same time, plants low in calcium (Ca), iron (Fe), magnesium (Mg), phosphorus (K), or silicon (Si) are also more likely to be sensitive to high manganese levels.
How plants use manganese
Manganese is used by all living things as an antioxidant, to counteract the toxic effects of oxygen. In plants, it is an important component of chloroplasts. Chloroplasts are where chlorophyll is made. Manganese is also used during photosynthesis, in many enzyme reactions, and to make potassium and calcium more readily available. Crops such as oats, wheat, and barley use a lot of manganese, with corn using moderate amounts.
Once inside a plant, manganese stays where it was first used. As a highly immobile plant nutrient, this means that deficiencies are most often seen in new growth, while toxicities are seen in older growth.
Plants can absorb too much manganese in acid soils, or under drought conditions. When acid-forming fertilizers, superphosphates (fertilizers made by treating phosphate rock with phosphoric or sulfuric acid) are used, or when nitrate (NO3-) is used as a nitrogen source, those acidic conditions can occur. Manganese is most available to plants when the soil pH is between 5.0 and 6.5. Soils with neutral or alkaline pH slow the solubility of manganese, so toxicities are less likely.
The most common symptoms of too much manganese look a lot like the symptoms of too much boron:
Too much manganese interferes with root growth and causes overall stunting, especially in alfalfa, small grains, and beans.
While magnesium is needed by all living things, too much magnesium can be very, very bad. At high doses, inhaled magnesium can lead to neurological damage called manganism, a condition similar to Parkinson’s disease. If you have to work with manganese, wear protective gear.
Being an immobile nutrient, manganese deficiencies are first seen in new growth. When manganese is in short supply, you will see interveinal chlorosis (yellowing between leaf veins). If there is a sharp distinction between veins and yellowing, it may be an iron deficiency, or a combination of insufficient manganese and iron. If this symptom is seen in older leaves, it is more likely to be a magnesium (Mg) deficiency.
Manganese deficiencies are more common in mucky soil, which means providing good drainage can prevent this problem. Cold and wet conditions can also interfere with manganese uptake. Due to its immobility as a plant nutrient, foliar (leaf) sprays of manganese are recommended if deficiencies have been identified.
Looking at plant leaves can tell you a lot about what they have and what they need.
Galls are the warts or tumors of the plant world.
Not really. Galls are neither warts nor tumors, but that’s how many of them appear. The word gall comes to us from the Latin galla, for ‘oak-apple’. Oak apples are not fruits. They are a plant’s reaction to the presence of a foreign substance. The study of plant galls is called cecidology [see-SID-ology]. Most commonly associated with baseball-sized knobs seen on oak trees, galls come in all sizes, and can be found on a variety of plants.
Galls are swellings that occur in response to invasion. That invasion may be in the form of bacteria, fungi, insect larvae, eriophyid mites, nematodes, or other pests, and even other plants. Mistletoe is one example of a gall-forming plant. Unlike fungal cankers, which involve plant tissue death, galls, fungal or otherwise, are cases of extra tissue growth.
Galls are nearly always woody knobs that may occur on stems, branches, roots, buds, petioles, flowers, fruits, or leaves. Galls may be simple, with a single chamber (unilocular), or highly complex, with many chambers (plurilocular). Galls can also look like a sphere, a saucer, pineapples, pinecones, pouches, pods, or fantastic, tiny red spikes. It just depends on the host plant and the cause of the gall.
Where they occur and what they look like inside can tell you a lot about what caused it.
If you cut a gall open, you will see distinctly arranged vascular tissues, depending on the cause of the gall, and an enlarged cambium layer. These distortions interfere with the flow of water and nutrients, which can lead to wilting and stunting. Or, you may see a large, open area, perfect for use as a larval nursery, with no noticeable impact to the host plant.
Insect, mite, and nematode galls
When insects invade a plant, the galls that form are built by the insect. These galls can act as food or shelter for the insects. This is different from the plant-produced domatia (tiny apartments) found in some thorns for beneficial insects. Insect galls are made when an insect injects chemicals (pseudo plant hormones) into the plant, causing the gall to develop. Very often, eggs are laid in these galls, providing developing larvae with food and protection. Gall wasps, sawflies, gall flies, scale insects, some aphid species, weevils, psyllids, and gall midges can all cause insect galls, but it is nearly always gall wasps or gall midges.
Nematodes are microscopic round soil worms that can cause small galls on roots. Root knot nematodes are one such pest. In each of these cases, the gall is made up entirely of plant tissue, unlike fungal and bacterial galls, which incorporate fungal or bacterial tissues, respectively. Insect galls may also house interlopers, technically called inquilines.
When a fungi infects a plant, it grows alongside plant cells, creating swollen areas that can develop into galls. Several varieties of rust can cause galls to form. When these galls form on conifers, as in the case of cedar apple rust, the galls look like gelatinous fingers, called telial horns.
Fungal galls on other types of leaves tend to look more spherical.
Bacterial and viral galls
Bacterial and viral galls develop because the bacteria or virus reprograms plant cells into producing more bacteria or viruses, or other supportive cells. When galls are found at or just below the soil level, it is, most likely, crown gall. Crown gall is a bacterial disease that can occur on blackberries, sunflowers, grapes, and roses, along with almond, apple, apricot, cherry, and pear trees.
Galls on roots may mean clubroot, a disease caused by an entirely separate group of parasites, known as Phytomyxea. Root galls may also mean the presence of beneficial, nitrogen fixing Rhizobium bacteria.
Galls have long been used in tanning, to make ink, and as astringents. Most galls contains high levels of tannic acid and resin. There even a few edible galls, but that is beyond my skill set.
Sometimes, what looks like a gall is actually caused by herbicide overspray.
Galls are most commonly formed when plant tissue is new and undifferentiated. This meristem tissue is most often seen in spring, so that’s when you should start looking for galls. Once gall development begins, the tissues have been reprogrammed and cannot go back to normal.
In a word, you can’t. Insect and mite galls rarely harm plants and you can’t completely control these pests anyway. Once they are inside the plant, there is nothing you can spray or apply that will even reach them. Anyway, the gall is already in place. Fungal and bacterial galls may, possibly, if you are really lucky, and can time it perfectly, be prevented or reduced with fungicide treatments. Or not.
If you are galled by galls, take them off. Otherwise, recognize that galls are just another amazing aspect of playing with plants.
Many slender-bodied insects, such as thrips and leafhoppers, are garden pests. Damsel bugs are an exception. Damsel bugs are predators. And they are very quick.
Damsel bug actually refers to most of an entire family of insects (Nabidae). Most damsel bugs are Nabis species.
Damsel bug description
Damsel bugs are true bugs (Hemiptera), which makes them cousin to many of their favorite foods. Whereas the “beak” (rostrum) is used by most true bugs to pierce plant tissues and suck sap, damsel bugs use their beak to inject digestive enzymes into victims. In either case, the beak is usually held under the body when not in use.
Damsel bugs have soft, slender bodies that may be brown, gray, yellowish, reddish brown, or tan. Adults are 3/8- to 1/2-inch long. They have long legs and long antennae, and may be confused with equally beneficial assassin bugs. Like assassin bugs, some damsel bugs can and will bite. They are, after all, predators. Medically speaking, as far as I know, damsel bug bites are harmless.
Damsel bug lifecycle
Young damsel bugs, or nymphs, look a lot like adults, which means they go through an incomplete metamorphosis. They have 5 developmental stages, or instars, before reaching adulthood. This process takes approximately 50 days. Adult females hide eggs by laying them inside plant tissue. Damsel bugs are most active in the Bay Area mid-June through mid-August, but they overwinter in ground cover and winter crops, such as alfalfa and many legumes. Remember, just because you don’t see them doesn’t mean they aren’t there.
Damsel bug prey
Like lady beetles and praying mantis, damsel bugs are generalists. This means they will eat whatever they can hold onto long enough to eat. Very often, those meals are aphids, armyworms, small caterpillars and caterpillar eggs, fleahoppers, leafhoppers, lygus bugs, mites, proba bugs, spider mites, and thrips. (Hooray for damsel bugs!) Of course, they will also eat beneficial big-eyed bugs and minute pirate bugs, and occasionally they will even eat plants, but their net result to the garden is still very positive.
In one study, it was estimated that a single adult damsel bug eats 42 moth larvae, 24 lygus bug nymphs, or 5 aphids every day. The same study estimated that a peak population of damsel bugs (283,000 bugs per acre) could consumer 12 million moth larvae, 6 million lygus bug nymphs, 1 million aphids, or some combination of those and other prey, every 24 hours. That’s some significant garden protection!
If you keep a hand lens in your pocket, you may be able to see a damsel bug up close one day.
Blackened roots, failure to thrive, yellowing leaves, and irregular stunting may all be signs of root rot, but not all root rots are black root rot.
Root rot might refer to the cabbage family’s black rot, asparagus’ Fusarium crown and foot rot, or phytophthora root and crown rot, which attacks a wide variety of plants and trees. And then there is black root rot. To tell the difference, you would need a microscope. But, knowing what to watch for can reduce your losses.
Black root rot is caused by a fungus (Thielaviopsis basicola). Yes, I know. It’s a strange word. [It is pronounced THEE-lay-vee-OP-sis.] But being able to pronounce the Latin isn’t as important as being able to recognize this plant disease before it spreads. Before looking for symptoms, however, you need to know which plants are susceptible to this fungal disease.
Black root rot host plants
Black root rot is a serious problem for commercial growers of ground covers, cotton, rice, many herbaceous perennials, snapdragons, tobacco, and our holiday poinsettias. Those lovely spring vinca, pansy, and viola plants can all carry this disease to your garden, even though they might look healthy in the store. This is why quarantining new plants is so important.
In addition to those nursery crops, black root rot can appear on several of your garden plants, including beans and peas, carrots, citrus, cucurbits, horseradish, lentils, melons, peanuts, soybeans, strawberries and other berries, potatoes and tomatoes. In many cases, you won’t see damage to roots until after harvest.
Conditions that favor black root rot
Black root rot occurs most often in cool, moist conditions. It is most likely when temperatures are between 55° and 61°F. Black root rot can be spread by fungus gnats and shore flies, and it is more commonly found in alkaline soil, such as we have here in the Bay Area. Fungal spores can also be spread via splashing rain or irrigation water, or on infected flats, containers, and garden tools. Soggy soil, poor drainage, and too much fertilizer all contribute to the likelihood of these soil-borne fungi taking hold of your plants.
Preventing black root rot
Once infection has become well established, the plant is a goner, so prevention is your only course of action. [Always throw diseased plants in the trash bin.] In severe cases, soil solarization may be needed to prevent infecting the next plants installed in that location. In commercial nurseries, chemical fungicides are used as preventive measures only.
The best way to avoid black root rot is to provide plants with good drainage, avoid overwatering and excessive use of fertilizer, and control fungus gnat populations with yellow sticky paper. Acidifying the soil can help somewhat, but soil pH is very difficult to change without ongoing treatments. Crop rotation can also interrupt this disease cycle.
Remember, mulching with arborist wood chips is one of the best ways to improve soil structure and drainage, reducing the chance of black root rot finding its way to your garden.
Gardening is a wonderful way to get exercise, grow healthy food, and improve your mental outlook, and good tools make gardening easier and even more enjoyable.
Whether your garden is a backyard plot, a sidewalk strip, or containers on a balcony, the right tools can protect your hands, your back, and your plants. That being said, some of the tools advertised as “impossible to do without”, well, you can do without. Also, while there are plenty of power tools in the world of gardening, rototillers, chippers, and tractors are not needed by the home gardener. [I really appreciate having a chipper, though!]
This guide provides an introduction to some of the more important garden tools, and introduces you to a few you may never have heard of before.
Pruners, shears, and loppers
If you only have one garden tool, make it a high quality bypass pruner. Pruners are used to clip away dead or diseased stems and leaves, to shape shrubs, trees, and espalier projects, and to harvest the fruits of our labors. Bypass pruners work much like scissors, in that the blades bypass each other to make a nice, clean cut. This makes it easier for plants to heal. Anvil pruners use a blade that cuts against a flat surface. This crushes plant material, but they are a good choice for cutting dead wood and woody stems.
Shears look like pruners with the blades turned sideways. Grass shears have shorter blades and are used around trees and shrubs, where a string trimmer might damage the bark. Hedge shears are a larger version used to shear shrubs and hedges.
For heavier cutting jobs, long-handled loppers are a good investment. For hard-to-reach cuts, pole pruners are a great choice, allowing you to trim the top of your trees without using a ladder. If you are like me and have arthritic hands, you can find pruners with a ratchet action, which provides increased cutting power.
Buckets and baskets
In my opinion, a sturdy, galvanized bucket is the second most useful garden tool, followed closely by a variety of baskets. Buckets can carry potting soil, water, weeds, chicken feed, tools, beverages, you name it, and baskets are great for carrying transplants, harvested fruits and vegetables, and other lightweight items. Buckets and baskets are simply too handy not to have, which is why I have several.
While every gardener dreams of having a Green Thumb, that doesn't mean you actually want your thumbs to turn green. Gardening barehanded is an easy way to develop cracked, stained skin and dirty, chipped nails. Of course, gardening barehanded feels good, and it increases the number of mood-boosting soil microorganisms you absorb as your play with your plants. But you will still want good gardening gloves. Believe me. Thorns and blisters are not fun.
When selecting gardening gloves, try on several different sizes and styles to see which ones feel the best. To test the "touch" aspect of your garden gloves, try picking up a dime from a hard, flat surface. Once you find a style and brand you like, be sure to grab several pair. You’ll be glad you did.
Unless you are gardening on a balcony or indoors on window sills, you will need more than a watering can to keep your garden hydrated. Garden hoses and soaker hoses come in many lengths, colors, and styles. You can control the way water comes out of your garden hose with an adjustable nozzle or water wand. Water wands provide a gentle, rain-like sprinkling. My husband swears by them, I prefer using my thumb. It is important,, when shopping for a garden hose, to ensure that the hose does not contain lead or other heavy metals. Lead is used in manufacturing most hoses, but it is probably not a good idea for your edible plants.
Pitch forks and spading forks look like dinner forks, only bigger. Pitch forks, or hay forks, have round tines and are used for pitching hay and flipping compost. Spading forks have flat tines that are used to turn the soil and lift plants out of the ground. Garden forks are handheld tools that look like a hand, with the fingers curled downward. A gardening fork is used to break up soil and when weeding. There are also potato forks, border forks, and broad forks, which you can read more about at the Garden Tool Company.
Shovels and trowels
Even if you employ no-dig gardening, sooner or later, you are going to need a shovel. A shovel is used to turn the soil, break up dirt clods, move materials around, and prepare beds for planting. Long-handled shovels are easier on your back, and short-handled shovels are better when working in tight spaces.
There are two basic types of shovel: rounded end and square end. The end of a shovel is called its point. Round point shovels are used for digging. They usually feature a shelf for your foot, to provide extra digging power. Square point shovels are better used for moving all that valuable mulch around. Shovels with especially sharp cutting edges are called spades. Narrow spades, used for digging trenches and installing transplants, are called drain spades.
Trowels are simply miniature, hand-held shovels. A trowel’s flat or curved blade surface is used to dig into and lift up soil, seedlings, and weeds without disturbing the surrounding area. Extra narrow trowels are called transplanters.
The most commonly used saw in the garden is the pruning saw. Pruning saws have a short handle and a short, curved blade, making it easy (usually) to work within a tree’s canopy. Bow pruning saws look more like hacksaws, with the blade held within an extended C-shaped metal handle.
Most hoes are long handled gardening tools with a small, thin metal blade, used to break up soil and in weeding. There are also handheld hoes, which are indispensable when it comes to getting to the root of problem weeds.
In addition to your standard, rectangular garden hoe, there are three other common garden hoes: the Warren hoe, the action hoe, and weeding hoes. The V-shaped Warren hoe is used primarily for digging furrows. The sharp-edged action hoe is a flattened circle used to cut weeds on both the push and pull strokes. There are actually several varieties of this type of how, which we will explore another day. Weeding hoes are double-headed in that they have a flat blade on one end and two pointed tips on the other end.
There are 3 basic types of rakes used in the garden: leaf rakes, cultivars, and thatching rakes. Leaf rakes feature flexible tines, gathered at the top into a triangular shape, that cause minimal damage to lawns while collecting fallen leaves. Cultivators are the comb-shaped variety, with metal teeth, used to move mulch, rocks, and soil. When cultivars have a T-shape, it is called a flat rake. When the head is held in place with two curved steel supports, it is called a bow rake. Thatching rakes use short, sharp blade-shaped tines, held horizontally, to scratch the soil surface and to remove thatch from lawns.
Other handy gardening tools include dibbles, brassica collars, moisture meters, a soil sampling tube, post hole diggers, edgers, stock panels, tree cages, tomato cages, canister sprayers, sticky barriers, brooms, tarps, rain barrels, knee pads… well, the list never really ends. Before adding to your tool collection, however, let’s take a look at common problems associated with garden tools.
Problems with garden tools
Dull tools are hard to work with and dirty tools can carry pests and diseases. If your tools are not well maintained, they can become dangerous to both you and your plants. A sharp, rusty edge can turn a small cut into a trip to the doctor’s office. Dull blades tear at plants, rather than making clean cuts. And if you don’t periodically sanitize your garden tools, well, you’re just asking for trouble. [Tools can be sanitized with bathroom cleaner or a solution of 1 part bleach and 9 parts water.]
There are a surprising number of mostly fungal diseases commonly spread by contact with infected tools. These diseases include Phytophthora tentaculata, Verticillium wilt, phytophthora root and crown rot, pink root, Fusarium wilt, Fusarium dieback, Fusarium crown and foot rot, eutypa dieback, stem blight, rust, rose rosette, peach leaf curl, onion white rot, mummy berry, karnal bunt, grey mold (also known as botrytis fruit rot and botrytis bunch rot), and cucumber mosaic. There are also bacterial diseases, such as angular leafspot, olive knot, black rot, crown gall, citrus blast (also known as bacterial blast or black pit), and blackleg that can be spread on contaminated tools. Conditions such as black spot, witches’ broom, bacterial wilt, and clubroot can also be spread by infected tools. Those tools can also carry vine mealybugs, nematodes, and San Jose scale to new plants.
Remember, pests and plant diseases are not the only things that get carried on tools - herbicides, pesticides, and tetanus bacterium can hitch a ride just as easily. Keeping tools clean is one way to break disease triangles and prevent accidental exposure.
How to clean rusted tools
It happens. You leave a tool outside overnight, or you decide, as I did, that your garden tools look lovely, hanging up against the chicken coop. Unfortunately, in each case, this exposes metal tools to water. Metal plus water equals rust. Compounding that problem, putting tools away without cleaning them leaves soil and microbes in contact with the metal surface, which can also corrode the metal. Even if you are diligent about cleaning and protecting your garden tools, they will still need regular care to work properly and last. Following these steps will help your tools stay useful longer:
So, what about those rarely heard of tools? How about a billhook? Or a sickle? Or a scythe? Scythes are those long-bladed tools you seeing being carried by Death or Father Time. If you ask my kids, they will tell you that scythes are implements of torture. This is due to my mother’s insistence that they help her mow a swath of path through her 97-acre Upstate New York farm one summer. Sickles are similar to scythes, but only smaller.
Billhooks are similar to sickles, but with a wider blade and an even shorter handle. Used to pull brush and vines closer, and then cutting them, billhooks, block hooks, and brishing hooks are commonly used in vineyards and when pleaching. Pleaching is the art of building living fences.
You want tools that fit nicely in your hands, that aren’t too heavy. It is important to buy garden tools that are well made. The demands put upon them often cause lower quality products to fail. I urge you to avoid poorly made, novelty tools.
Ultimately, all your plants need is good soil, plenty of sunlight, and an occasional rain. But well made, properly maintained tools can make the task of gardening a lot easier on your hands and your back.
Finally, does anyone know what the tool below is called? I inherited it from my mother, but I haven't been able to track down a name.
Before placing a bare root tree or containerized plant in the ground, be sure to check for girdling roots.
Girdling roots work very much the way your grandmother’s elastic undergarment did, in that they cut off circulation and restrict movement. Girdling roots can kill your tree.
What is girdling?
To ‘girdle’ means to surround something, to go around its girth. When girdling happens aboveground, it refers to the removal of a ring of bark. This bark contains the cambium layer, which houses the vascular bundles that transport water, oxygen, and nutrients. It often occurs when tree supports are left on for too long or installed improperly. Girdling roots create the same problem by encircling the trunk and neighboring roots, effectively cutting off the supply of water, oxygen, and nutrients. Wherever girdling occurs, whatever lies beyond the girdle will, in most cases, die.
In a normal, healthy tree, perennial roots reach out horizontally, anchoring the tree in place and providing a pathway for water, oxygen, and nutrients to enter the body of the tree. Those important elements move through the xylem of transport roots, after being collected by feeder roots. Unless they can’t.
Sometimes, containerized plants become root bound. If you take the plant out of its pot, roots can be seen circling around, looking for a way out. As these roots get bigger in diameter, they slow or halt the transport of life-giving water, oxygen, and nutrients, effectively choking itself to death. This often starts with improper planting depth.
Roots emerge from the body of the tree just below the root collar, or where the trunk flares out. [If you plant a tree and it looks like a pencil sticking out of the ground, it is planted too deeply.] If the root collar is buried, as often occurs with modern, mass-produced trees, they become predisposed to girdling roots, as well as pest infestations and fungal diseases. This also places the roots deeper in the soil, where it is harder for them to access the water, nutrients, and oxygen they need.
Symptoms of girdling roots
In some cases, girdling roots can be seen simply by looking at the base of the trunk.
If the problem is occurring underground, you may still be able to identify the problem when these symptoms are seen:
In severe cases, the bole indentation can create structurally weak areas that are prone to twisting or breaking. Of course, these symptoms are not always seen. In many cases, a tree will struggle on, growing but not thriving. Within 2 to 10 years, the tree dies for no apparent reason.
How to prevent girdling roots
When you plant a tree or shrub, start by inspecting the root system. Loosen and straighten any circling roots. Roots that have been circling for more than two years will be too woody to straighten and should be removed.
Next, make sure that the planting hole is the proper depth and diameter. Do not “spin” roots into a too small hole. Dig the hole wide enough to allow the roots to spread out horizontally. While wider is better, deeper is not. Dig the planting hole only as deep as is needed for the roots to be just below the soil surface. Planting it any deeper than that is setting the stage for failure.
When planting in compacted soil, it is important to loosen the surrounding soil, or the new roots will simply circle around in this new 'container'. Other obstructions, such as building foundations or large rocks can also caused girdling roots. Mulching the area with arborist wood chips is an excellent way to (slowly) reduce compaction while keeping down weeds, stabilizing soil temperatures, and retaining moisture.
Responding to girdling roots
Giving a tree with girdling roots more water and fertilizer will not fix the problem.
Girdling roots must be removed if a tree is to survive. These roots should first be exposed by removing the surrounding soil. Then, 6 to 12 inches from the trunk, the girdling roots must be cut away, usually with a chisel or a saw. This first cut is to prevent damage to the trunk, in case there is any tension being placed on the root. [An apple tree with a 20” diameter trunk can weigh nearly 2-1/2 tons, so tension is definitely occurring somewhere!] The final cut is made where the root meets the trunk. If it is possible to remove the girdling root(s) without disturbing the surrounding roots, do so. Otherwise, leave it where it is and it will, eventually, decompose.
Especially large girdling roots must be removed in stages by a professional arborist. To cut it off abruptly would eliminate the supply of too much water and nutrients to the tree, putting the entire tree at risk.
Tree roots provide the life blood of the tree. If those roots start circling, corrective measures must be taken for the tree to survive
Chickweed may sound like a 1970’s party girl, but the name actually refers to several common California winter weeds that can harbor pests and diseases.
There are three species of chickweed found in California and they all germinate quickly and in abundance, under the cool, moist conditions common to California winters. Chickweed can complete its lifecycle in as little as 5 weeks, with each plant producing 800 seeds. If a single chickweed plant goes to seed in your garden or landscape, it can take 8 years before the seeds of that first plant are no longer viable. Be on the lookout for chickweed seedlings from January through the end of March.
Native to Europe, common chickweed (Stellaria media) is now found in many regions of North America and Asia. Also known as winterweed and chickenwort, common chickweed has been used as food and herbal remedy, though there is little or no scientific research to back up claims of common chickweed’s ability to provide cooling relief. Many people find the taste of this somewhat succulent annual too bitter to enjoy. Common chickweed contains high levels of iron, but the bitterness is caused by saponins, which can be toxic in large quantities.
Common chickweed is differentiated from its non-edible cousins by fine hairs found only along one side of the stem, whereas other, non-edible chickweeds have hairs all around the stem.
Succulent leaves grow opposite one another, and have a pointed tip. Common chickweed can reach 4 - 6” in height, but it generally grows as a short, dense mat, especially in lawns. The roots are fibrous and found near the surface. Stems tend to be weak, and plants produce white flowers and seed capsules at the same time. Common chickweeds plants have 5-petalled flowers, but each petal is split, to create the appearance of 10 petals.
While grown as poultry feed and ground cover, common chickweed provides food and shelter for lygus bugs, thrips, pale-banded darts or spotted-sided cutworms (Agnorisma badinodis), and dusky cutworms (Agrotis venerabilis). Common chickweed can also carry cucumber mosaic virus and spotted tomato wilt virus.
Mouse-ear chickweed (Cerastium fontanum ssp. vulgare) is taller than other forms of chickweed, reaching 4 - 8”. Hairy leaves grow opposite each other in a star-shaped pattern. This weed grows horizontally by putting out roots wherever the stem, which tends to fall over, touches the ground. Flowers are tiny and white, with 5 petals. The fruit capsules are brown and somewhat crescent-shaped.
Removing chickweed is difficult. Under cool, wet conditions, chickweed plants may send out roots at the nodes, which means every tiny piece of chickweed is a potential new plant. Thick layers of mulch and hand weeding, preferably before plants go to flower, are really the only organic methods of control. Heavy infestations can be managed with soil solarization. Unless you are feeding these weeds to your chickens, it is better to get them off your property completely, to avoid reseeding.
Ploughing or rototilling the area can reduce chickweed germination, but you may simply be trading one problem for another, as other weed seeds are brought closer to the surface. Maintaining a thick, vigorous lawn is another way to reduce the number of chickweed seedlings that make it to adulthood. Allowing your lawn to be taller than a putting green can reduce the amount of sunlight that reaches chickweed seedlings.
Before you completely write off common chickweed as undesirable, you need to know that it is also one of the preferred foods of the rare dainty sulphur moth (Nathalis iole).
How can you use soil test results? You could ask Mulder.
Garardus Johannes Mulder was a chemist who lived in the 1800s. Now, we have learned a lot about plant and soil science since the 1800’s, but Mulder came up with a chart that gives us some insight into how the minerals used by plants as food might interact.
Before we learn how to use Mulder’s Chart, let’s review soil pH and nutrient absorption.
The 20 or so minerals used by plants as food are found in soil as ions. Ions are atoms and molecules that have either a positive or negative charge. These cations and anions, respectively, attach themselves to water molecules and are pulled into the plant by root hairs. The ability of a plant to pull those nutrients in depends largely on soil pH.
Soil pH ranges from 0 to 14, with lower numbers indicating acidity and higher numbers indicating alkalinity. Using the chart below, you can see that more nutrients are available, and there is greater microbial activity, when soil pH is between 6.0 and 7.0. Most plants can survive in soil pH from 5.2 to 7.8, but the narrower range allows plants to thrive. As anions and cations are pulled out of the soil, the soil pH changes, ever so slightly. This is why too much or too little of certain minerals in the soil may interfere with nutrient availability. This is where Mulder’s Chart comes in.
How to use Mulder’s Chart
Looking at Mulder's Chart, you can see 11 essential plant nutrients and micronutrients arranged around a circle. Solid and dotted lines connect the nutrients, with arrows heading one way or the other. Solid lines indicate an “antagonistic” relationship, which means high levels of one nutrient leads to a problem absorbing the nutrient being pointed to, while dotted lines indicate a “synergistic” relationship.
For example, according to Mulder’s Chart, high levels of nitrogen may reduce a plant’s ability to absorb boron, copper, and potash, as seen by the solid lines pointing from nitrogen toward the other nutrients. In the same way, high levels of nitrogen may stimulate magnesium uptake, and high levels of molybdenum might stimulate plants into absorbing more nitrogen, as seen by the dotted “synergistic” lines. Like most things in life, though, it isn’t really that simple.
Until you have a soil test from a reputable laboratory, you cannot know what is in your soil. Soil test results provide an amazing snapshot of what is really going on “down there”. Your soil test results will include individual measurements of several plant nutrients, as well as a cation exchange capacity rating, which describes a soil's ability to hold nutrients.
According to Linda Chalker-Scott, associate professor of horticulture and extension specialist at Washington State University, “It makes sense from a strictly chemical point of view, but soils are also biological. Plants exude organic acids from their roots. Mycorrhizae can mobilize "immobile" nutrients. I find these types of charts way too simplistic for real world conditions.”
While there is certainly a limit to its usefulness, I do encourage you to apply Mulder’s Chart to your soil test results and compare those results to what you are seeing in your garden. It may give you an idea of where problems may be occurring, or it might just be a fun way to review your soil test.
Boron isn’t nearly as boring as it sounds, once you know what it does for your plants.
Members of the cabbage family use a lot of boron, while peas and beans, peppers, and sweet potatoes need very little. Before you start adding boron to your garden soil, let’s take a closer look at what this element does for and to our plants.
Boron (B) is a micronutrient. In the world of plant food, micronutrients are only used in tiny amounts, but they are very important to plant growth. The optimal range for boron found in a soil sample is 0.1-0.5 parts per million (ppm). The only way you can determine how much boron is in your soil is with a laboratory soil test. Take my word for it, it’s the best investment you can make in your garden, next to mulching. But back to boron.
How do plants use boron?
Boron is critical for cell wall development and function, making those cell walls both strong and porous. The plasma membrane that allows molecules of sugar, water, wastes, and gases to move in and out of a cell rely heavily on boron to function properly. Research has also shown that boron is used by plants to produce and transport sugars within the plant, in protein synthesis, seed and pollen grain development, pollen tube growth, and flower growth and retention. Boron also plays important roles in nitrogen metabolism and fixation, the accumulation of the chemicals that affect taste (phenols), and in root development.
Boron, is most easily absorbed when soil pH is 5.5 to 7.5. First absorbed through root cells, boron then moves into the xylem, where it is taken to new leaves and shoots, or into the phloem, where it is taken to reproductive tissues, as well as vegetative tissues. Once boron is absorbed by a plant, it stays where it was placed. This is because boron is not a mobile plant nutrient. This is useful information because it means boron deficiencies will tend to show up in new growth before being seen in older leaves.
Helping plants get the boron they need
Boron is commonly leached out of the soil, leading to deficiencies, in areas with heavy rainfall. In drought-prone regions with very little rainfall, boron can build up in the soil, leading to potential toxicities. This is especially true for alkaline soil, or when too much fertilizer has been applied. [Just because a plant looks unhealthy does not mean it needs more food.]
Nutrient imbalances can make it difficult for a plant to absorb the nutrients it needs, even when those nutrients are present in the soil. For example, too much potassium in the soil can interfere with a plant’s ability to absorb boron, along with several other important nutrients. [The optimal range for potassium is 100-160 ppm.] Calcium and boron ratios are also very important to plant health. We will take a closer look at a tool, called Mulder’s Chart, that shows how these interactions work, in my next post. For now, we will look at what too little or too much boron can do.
Boron toxicity occurs when boron levels are at or above 1.8 ppm. Too much boron negatively impacts plant metabolism, and it reduces root and shoot development, chlorophyll production, rates of photosynthesis, and the lignin and suberin needed for structure and protection.
Toxic levels of boron can often be identified by looking at plant leaves. Too much boron will appear as either necrosis (death) or chlorosis (yellowing) of leaf tips and edges (margins). These damaged areas are believed to occur because the overabundance of boron interferes with several life processes, all at the same time. Unfortunately, these are the same symptoms as caused by magnesium deficiencies. [Can you say laboratory soil test?]
Adding extra boron is easy, when more is needed. Getting rid of excess boron requires more effort in the form of improved drainage through the addition of more organic material. Obviously, this takes time.
Insufficient or unavailable boron in the soil is the world’s most widespread micronutrient deficiency. It is a common problem in soils with low levels of organic matter (<1.5%). Boron deficiencies lead to reduced crop size and quality but symptoms can vary, depending on the crop:
Too much, too little, or no way for plants to get to the boron they need can all cause problems. Getting a laboratory soil test is the only way to know what’s eating your plants, or rather, what your plants are eating.
Autotoxicity is a form of chemical warfare found in the plant world, and it might be happening in your garden or landscape. Or, it might be an unsubstantiated biological process that looks great on paper, or works out well in a laboratory petri dish, but doesn’t hold as true in the field.
In either case, it is good know what the concept claims, which parts have withstood the tests of time and science, and how it might impact your garden. Let’s start with basic competition for survival.
We know that plants compete with their neighbors for real estate and resources. Those resources include water, sunlight, nutrients, beneficial soil microbes, and access to pollinators. Over time, plants have found different ways to gain an edge over the local competition. Many weeds have evolved to grow faster, in order to find resources first, while other plants grow taller, to commandeer available sunlight. Other forms of competition occur when plants develop deeper or wider spreading roots, which can reach more food and water, or more flamboyant, heavily scented flowers, to increase pollination rates. In some cases, plants have evolved to use chemicals on their neighbors.
Chemical warfare among plants
Oblivious to the Geneva Convention, some plants release chemicals through their roots, leaves, and stems that impact neighboring plants. When those chemicals affect other species, it is called allelopathy [al-el-ah-path-ee]. Allelopathic plants release chemicals that can either stimulate or inhibit the life processes of other plant species. When those chemicals only affect plants of the same species, it is called autotoxicity. Autotoxicity can only inhibit, and never stimulate, the growth or germination of plants of the same species. But why would a plant want to treat family members that way?
The word ‘autotoxicity’ means ‘self-poison’ and it is used to describe the way some chemicals are believed to only negatively impact plants of the same species. From a survival perspective, on the surface, this might make sense. Members of a species all need the same resources to thrive. If there are too many of one species growing in the same place, those resources can be used up before any individual plant has time to reproduce, except that it isn’t that simple. Let’s take a closer look at which plants are said to be autotoxic and how autotoxicity is said to work.
Alfalfa is acknowledged as an autotoxic plant. How can this be, you might ask. Alfalfa is grown in immense fields, the same way corn, oats, and other similar crops are grown, with other alfalfa plants on every side, isn’t it? It is. But, underground, soon after alfalfa seeds germinate, seedlings start producing toxins that reduce germination and prevent the growth of root hairs in other alfalfa plants. Without root hairs, neighboring plants cannot absorb water or nutrients. So, why aren’t all the nearby alfalfa plants dead?
The trick lies in the fact that these chemicals are not released until the seedlings have gone through their full lifecycle and died. As the plants were busy maturing, the levels of these toxins continued to increase, but those chemicals only impact the next crop, as the dead plant material decomposes. Because of this, crop rotation is commonly used when growing alfalfa commercially.
Alfalfa autotoxicity on root growth. Taproots of plants planted within 2 weeks of an existing alfalfa stand having been tilled under, resulting in formation of branched roots that are less effective in nutrient and water uptake. Taproots of plants seeded 18 months after tillage of an existing alfalfa stand (right) possess the normal, carrot-shaped root. Photo credit: Dr. John Jennings, University of Arkansas.
According to one Canadian study, several other edible plants are said to be impacted by autotoxicity. Their list includes rice, wheat, corn, soybeans, sugarcane, cucumber, ginger, muskmelon, watermelon, asparagus, tomatoes, citrus, tea, and coffee. The problem with the science behind autotoxicity lies in the fact that some of the chemicals cited as autotoxins, such as p-coumaric acid, are found in many other plants, with no ill effects. Also, in much of the current research, autotoxic chemicals are applied artificially, which may or may not involve all the steps that might occur in nature.
When we apply compost to an area of the garden or landscape, we are introducing a variety of chemicals. In the case of small home gardens, the diversity of plant materials found in a compost pile generally reduces any potential autotoxic affect to negligible levels. Using no-dig gardening and cutting used up plants off at soil level, rather than pulling them out by the roots, leaves these potentially autotoxic roots in the soil. This may or may not create a problem, but it is something to keep in mind.
Whether autotoxicity is a real problem or not, you now know more about it than most people. And remember, before you accept opinion as gospel, make sure there is enough good science behind it to make it worth your time and effort.
Yeast may help bread rise, beer froth, and wine ferment, but what does it do in the garden?
Is yeast a plant? An animal? Actually, yeast is a one-celled, sugar-eating fungus that urinates alcohol and farts carbon dioxide. It is those farts that make bread rise, and the other excretion that puts alcohol into beer and wine.
Yeasts have been around for hundreds of millions of years. In many ways, yeasts and other fungi are a lot like plants, but they are different in many ways, too.
Yeast vs. plant cells
Yeast cells are smaller than plant cells. While plant cells can become leaf, stem, fruit, or root cells, yeast cells remain the same one-celled creature. Like plant cells, yeast cells have a cell wall, but it is not made out of cellulose. Both yeast and plant cells have membranes, but they are made out of different materials. Yeast cells do not have chlorophyll-producing chloroplasts, either, which is why they do not use sunlight to make food. Inside a plant cell, you can find food stored as a starch, whereas yeasts store food as sugar.
Other common fungi include mushrooms and molds. The yeast you buy in the store to make bread, beer, or wine is called Saccharomyces cerevisiae.
How do yeasts grow?
Yeasts do not require sunlight to grow. Yeasts feed on dead, decaying matter, making them saprophytes. They are also parasites, which makes them heterotrophs. Instead of using the sun’s energy to generate food, fungi absorb carbon, in the form of sugars, organic acids, and other easy-to-digest carbon-based edibles from their hosts. This is why you will often see fungi growing on the skins of apples, grapes, or peaches. Yeasts grow best when the environment has a neutral or slightly acidic pH.
Yeasts reproduce in a variety of ways, depending on the species and environmental conditions. The most common method of yeast reproduction is an asexual, vegetative method called budding. In budding, a clone offspring is produced as an attachment to the parent cell. When the clone, also known as a bleb or daughter cell, reaches maturity, it separates from the parent cell, leaving behind scar tissue. In some cases, these buds can link themselves together into chains, called false hyphae. Other yeasts reproduce using mitosis. In mitosis, the genetic information is duplicated and the nucleus of the cell is split in half, with each half being a twin to the other. Fission and meiosis are also used by some yeast species, but we digress
Harmful yeasts in the garden
Yeasts love to eat sugar. As such, they can spoil fruits and vegetables before you ever get a chance to enjoy them. Yeasts can grow on almonds, pineapples, lettuces, and pretty much anything else you decide to grow. Peach leaf curl is also caused by a yeast. That being said, yeasts actually perform many beneficial services to your garden.
Beneficial yeasts in the garden
Yeasts are not all bad. When it comes to protecting your strawberries, cherries, and cane fruits from the invasive spotted wing drosophila, torula yeast is used to lure this pest to its death. Also, recent research has demonstrated that adding brewers yeast to the garden may help plants counteract the effects of toxins in the soil. In another amazing study, it was found that a yeast found on the bodies of pollinating bees gets knocked onto flowers, as bees move around. Those yeasts then feed on the sugars in the flowers’ nectar. Breaking down those sugars generates heat, which keeps the flowers and the surrounding air space (used by the bees) warmer. This helps both parties survive winter. Yeasts also play a role in soil aggregate formation, improving soil structure. While other yeasts are believed to be part of the sulfur and nitrogen cycles, and make insoluble phosphates available to plants. Yeasts are food for many bacteria, insects, and other soil predators.
If nothing else, adding yeast to the compost pile will speed decomposition, assuming moisture and temperature levels are appropriate.
Did you know that some yeast species produce toxins that kill off other yeast species?
Now you know.
What looks like a light dusting of snow may actually be life-threatening pests, called adelgids.
Like their cousins, the aphids, adelgids pierce vascular bundles to suck out nutrient rich fluids. While mature, healthy trees can withstand a mild adelgid infestation, saplings, young trees, and unhealthy trees can be killed by this tiny, soft-bodied pest.
Scientists are still trying to nail down adelgid classification. There are 50 known species, all of which are native to the northern hemisphere, though several invasive species have made their way into the southern hemisphere. The most commonly found adelgids in California include the invasive balsam wooly adelgid (from Europe), the Cooley spruce gall adelgid (Adelges cooleyi Gillette), and pine adelgids.
Adelgids are commonly found on stone pine and other conifer species, such as pine and spruce. Depending on the host plant, the pests are commonly known as “pine aphids” or “spruce aphids”, respectively, even though they are not actually aphids. [Thanks to my friend, Chuck, I now know that adelgids are also found on apple trees. Thanks, Chuck!]
Aphids vs. adelgids
Aphids are significantly larger than adelgids, and they have two structures that adelgids do not: cornicles, and a tail-like cauda. Cornicles are tubes found sticking out of the 5th or 6th abdominal segments. These tubes are used to excrete a defensive chemical wax. Contrary to popular belief, cornicles are not used in honeydew distribution. Adelgids are covered with a dense wooly wax, so it is easy to mistake them for wooly aphids. This white fluff may be found on twigs, needles, bark, or cones.
Unlike aphids, which reproduce using both eggs and live birth, adelgids only lay eggs. Adelgids generally live for two years and each female can lay from one to several hundred eggs, depending on the species. Adelgid nymphs are called sistentes, which comes from a Latin that means ‘to stand’. When these sistentes overwinter, they are called neosistens. Some adelgid species require six generations to complete their lifecycle, moving between different tree species. Much like the Monarch butterfly, these insect pests do not live long enough to complete migration as individuals. Generally, it is only the immature stage that causes damage.
Damage caused by adelgids
Heavy infestations can cause yellowing, drooping, and dieback of twig tips. As they feed, adelgids release toxins that interfere with the tree’s ability to produce conductive sapwood. Eventually, the tree suffers severe water-stress and dies. These infestations can appear as swollen twigs, galls, or twig dieback. Adelgid galls look like tiny pineapples and can be green, red, or purple. The initial damage is usually seen on the underside of buds, before infestation and damage spread to the entire bud.
These pests are easily dislodged with a stream of water from your garden hose, but that only works you see them, which means you have to go outside and look. Beneficial predators, such as lady beetles, green lacewings, and some fly larvae. Horticultural oils can slo be used, but they will discolor spruce tree needles.
Infested twigs can be pruned out while they are still green (before adelgids have emerged) and thrown in the trash. Also avoid applying excess nitrogen, which can stimulate vulnerable new growth.
The National Park Service estimates that adelgids are responsible for the death of 90% of the mature fir trees found in the Great Smokey Mountains National Park, since this pest’s arrival in 1962. If you have conifers on your property, it is a good idea to inspect them periodically for signs of adelgid infestation.
Potato tuberworms are a minor to moderate pest, but they can make your potatoes inedible.
Also known as the potato tuber moth or tobacco splitworm, potato tuberworms (Phthorimaea operculella) love to feed on members of the nightshade family, such as eggplants, tomatoes, peppers, and tobacco, but they prefer potatoes.
The potato tuber moth is unique in the moth world in that her ovipositor (egg-laying organ) has sensors that can pick up chemical signals given off by potato plants. [If you are really into this sort of thing, the chemical signal is an amino acid called L-glutamic acid. But don’t worry, there won’t be a quiz.] She doesn’t necessarily have to be on the potato plant to lay her eggs, either, but you can be sure she will be close. These moths are usually seen an hour or two after sunset.
Potato tuberworm description
Potato tuberworms are the larval form of a small grayish-brown moth. The adult moth has a 1/2-inch wingspan and dark grey or black markings. At rest, both sets of fringed wings are held close to the body, giving them a slender appearance. Females moths have a distinctive “X” pattern on their forewings when at rest.
Eggs are very tiny, oval, and yellowish white. The larvae, or caterpillars, are just under 1/2 an inch in length, and their color can vary, depending on what they are eating, from white or grey, to tan, pink, or yellowish. Larvae have a brown head and prothoracic shield. [A prothoracic shield is the segment just behind the head.] Cocoons are 1/2 an inch long and pale colored.
Potato tuberworm lifecycle
Each female potato tuber moth will lay over 200 eggs in her short lifetime. Those eggs are normally laid next to a leaf vein, near a bud, or under a stem, though they can also be found in the soil near a host plant. In five days, those eggs will hatch. For the next two weeks, the larvae will eat as much as they can. The way they decide where to feed may surprise you. This is not a simple case of taking bites out of whatever is at hand. Nay, nay! Our newly hatched potato tuberworm larva will spend the first 5 to 15 minutes of its life walking around on its home plant. As it walks, it attaches a silk thread to the plant every few steps, turning this way and that way, taking an occasional bite as it meanders. If it has hatched on an unacceptable plant, the larva will walk faster and ultimately leave the plant altogether, until it can find an acceptable host plant.
Damage caused by potato tuberworms
Young potato tuberworm larvae might burrow through leaves and stems, causing stunting and reduced crop size. As feeding and tunneling continue, the tuberworms head for their favorite food: your potatoes. Webbing and frass (bug poop) deposits can be seen at entry holes, normally found at the eyes of a potato. While other pesky tunneling insects, such as wireworms and leaf miners, tend to keep their tunnels neat and tidy, potato tuberworms are slobs. Those dark tunnels are filled with excrement.
Controlling potato tuberworms
Row covers can be used to prevent adult moths from laying eggs on your potato plants. The deeper your potatoes are growing, the more difficult it is for tuberworms to get to them, so selecting a deep growing variety is helpful if you know tuberworms are around. Also, avoid furrow irrigation, which can cause cracks in the soil. These cracks are used as elevators to lower soil levels by tuberworms. Research has shown that insecticides do not prevent potato tuberworm infestations when erosion or soil cracks are present, or when potatoes are left in the ground longer than is necessary. Finally, harvest potatoes as soon as they are ready. Infested potatoes should be thrown in the trash and not added to the compost pile. Heavy infestations can be treated with spinosad.
Scabby potatoes? Yuck!
What causes this condition, and how can it be prevented?
First classified as a fungal disease, we now know that potato scab is a bacterial disease caused by Streptomyces scabies. There are other strains of Streptomyces that cause other potato diseases. S. scabies is found in the soil pretty much any place potatoes are grown. This bacterium can infect young seedlings of any plant, but it is most commonly associated with root and tuber crops, especially potatoes.
Delicious twice-baked and cut into wedges, served with sour cream and butter, potato skins are actually the cork, or periderm, layer normally found underneath bark. This layer normally provides protection from pests and disease. You may see tiny nicks of color in a potato’s skin. These are called lenticels and are used for respiration. This is also where the S. scabies bacterium gets in and starts infecting a potato.
Symptoms of potato scab
After entering a potato through a lenticel or wound site, S. scabies start setting up house. As they feed and reproduce, these bacteria release toxins into the surrounding plant tissue. The first sign of potato scab is nothing more than reddish-brown spots on the potato skin. These spots expand as the potato grows, becoming corky and necrotic. Then, the bacteria start reproducing (sporulating) in earnest, producing different types of lesions, depending on host resistance, time of infection, the aggressiveness of the bacterial strain, and other environmental conditions.
There are three basic types of lesions caused by potato scab: russet, erumpent, and pitted.
How to prevent potato scab
Being a seed and soil borne bacteria, potato scab is best prevented by manipulating soil moisture, soil texture, and soil pH, and planting healthy stock You won’t get rid of the bacteria completely, but you can significantly reduce their numbers with these tips:
You can still eat potatoes infected with potato scab, but you should probably cut out the lesions and toss them in the trash.
Potato psyllids (Bactericera cockerelli) are disease-carrying, life-sucking plant lice. These invasive pests also feed on tomatoes and other members of the nightshade family, along with several other garden plants.
Potato psyllid description
Potato psyllids are tiny. When I say tiny, I mean that an adult potato psyllid could stretch out comfortably across the edge of an American nickel, without dangling. If you get close enough, preferably with a hand lens or magnifying glass, you would see that they look like miniature cicadas. Potato psyllid adults are black, with a white band across the first abdominal segment and an inverted “V” on the final segment. They have clear wings that are held roof-like over the body when not flying or jumping. [They jump a lot.]
Potato psyllid lifecycle
Potato psyllids start out as eggs. Each female lays approximately 200 eggs, each of which hatches in 6 to 10 days. Those eggs look like microscopic footballs held to the underside of leaves with short stalks. [Do not mistake those short-stalked eggs to the longer stalked, beneficial lacewing eggs.]
After those eggs hatch into green, fringed nymphs, they look more like whiteflies or soft scale insects. Then, they go through five developmental stages, also known as molts or instars. Under ideal conditions, all that growing can be completed in less than two weeks.
Damage caused by potato psyllids
If sucking nutrient rich plant fluids wasn’t problem enough, potato psyllids cause other problems, too. For one thing, as nymphs feed, they release a toxin that can kill young transplants. This toxin also causes upward curling of leaflets closest to the stem on the upper portions of the plant. This condition is known as “psyllid yellows” or “vein greening”. The characteristic yellowing usually starts along leaf margins and then moves inward, turning purple in some cases. As this condition worsens, nodes [bumps where leaves emerge] become enlarged and closer together, rosetted clusters of leaves emerge from axillary (or lateral) buds, and aerial tubers begin to form. Aerial tubers grow at the end of aboveground stems, as opposed to underground stems, the way proper potatoes grow. When this pest feeds on tomato plants, it can cause no fruit production or overproduction of poor quality fruits.
Eventually, the once green, bushy potato plant looks more like a pitiful yellow Christmas tree. [If chlorosis is spotty and leaf rosetting is not present, the problem is more likely to be calico virus.] If potato psyllids are removed from the plant, the condition will stop progressing.
Potato psyllids are also carriers of another condition, known as zebra chip. Zebra chip is a bacterial disease that causes potatoes to store sugar, rather than starch. That might sound like a great idea for a new dessert food, but the presence of sugars cause ugly brown lines across the length of the potato. When cooked, these brown lines turn black, hence the name. This condition reduces crop size by 20 to 50%. Healthy appearing potatoes from plants affected by zebra chip are more likely to sprout while in storage.
Managing potato psyllids
You can’t control potato psyllids if you don’t know where they are. The first step to managing potato psyllids is to use yellow sticky traps. You can buy these at any garden center, or you can make your own with some yellow paperboard and sticky barrier goo. You should also inspect the undersides of leaves, looking for nymphs. While you’re at it, you should probably check the underside of any nearby bean or pepper plants, as these may also become infested.
In commercially grown potato fields, where potato psyllid is known to occur, a type of systemic neonicotinoid neurotoxin, called imidacloprid, is applied. [While not yet noted in California, resistance to imidacloprid has been documented in Texas.] Organic growers, like myself, use spinosad.
Because potato psyllids are not native to California, our local team of predators, which include lady beetles, lacewing larvae, and minute pirate bugs, have not been very effective at controlling this pest. Not yet, anyway.
You can grow a surprising amount of food in your own yard. Ask me how!