The Daily Garden is all about plant vocabulary. Today, we are looking at overall plant anatomy because it can be difficult to talk about something if you don’t know the words.
By taking a closer look at plant anatomy, we will be better able to understand each other, we can get more out of plant descriptions, and be better able to identify those mystery plants that always seem to pop up in the yard.
Plant anatomy, or phytotomy, starts with simple descriptions of the outside and inside of plants. Remember those black-line masters from grade school used to teach parts of a plant? Well, let’s start there.
Basic plant systems
Plants are have two basic systems: roots and shoots, with the root system below ground and the shoot system above ground. Roots provide anchorage and often store nutrients. Roots can develop as a taproot or fibrous root system. Roots have hairs that absorb water and nutrients. The shoot system consists of vegetative parts (leaves and stems) and reproductive parts (buds, fruits, seeds, and flowers or cones). Let’s take a closer look at each of those parts.
Leaves are the sugar factories of the plant world, absorbing sunlight and converting it into sugar through photosynthesis. The wide, flat part of a leaf is called the blade, or lamina. The shape of the leaf blade is very useful in plant identification, as is the way those leaves are arranged along a stem and the pattern of veins within a leaf. The edge of the leaf is called its margin. Leaves are coated with a waxy protective cuticle. There are tiny holes, usually found on the underside of a leaf, called stoma, that allow plants to exchange gases with the environment and to regulate water flow within the plant. The stem that connects a leaf to a stem is the petiole. Leaflike structures seen at the base of the petiole are called stipules,
Stems support leaves, flowers and buds. These structures are attached at nodes. The spaces between nodes are called internodes. Herbaceous stems have waxy cuticles for protection while woody plants have bark. Stems contain a vascular system that consists of the xylem, phloem and may include a cambium layer. This system carries food, water, and minerals throughout the plant. That vascular system is arranged in a circular pattern in dicots and eudicots, while it is more scattered in monocots. Twigs are woody stems from the previous year. Branches are more than one year old and may have lateral stems. Trunks are the main stem of woody plants, such as trees and shrubs. Canes are a type of stem filled with spongy pith. Canes generally only live for a year or two. Modified stems occur both above and below ground. Bulbs, corms, rhizomes, and tubers, such as potatoes, are below ground modified stems. Crowns, spurs, and stolons are aboveground modified stems. Thorns are also modified stems, but rose thorns are not really thorns. They are prickles, which are modified epidural, or skin cells. Stubby stems, called spurs, produce fruit buds.
Buds are shoots that may develop into leaves or flowers. Buds are identified by their location on a stem: lateral buds are found along the sides of a stem, while terminal buds are found at the end. Lateral buds usually grow where leaves meet the stem and are called axillary buds. Renegade adventitious buds may show up at injury sites, on roots, or even at the edge of a leaf. The place where buds fall off leave a mark called a bud scar. Tree leaf buds have scales, while leaf buds of annuals and herbaceous perennials have delicate naked buds. Potato eyes are clusters of buds.
Fruits are ripened plant ovaries. Fruits can be simple (formed with one ovary), as in the case of stone fruits, or compound (formed with several fused ovaries). Compound fruits can be multiple or aggregate. Apples and other pomes are multiple compound fruits. You can tell by the 5-pointed star shape in the center of the fruit. Raspberries, which are drupes, not berries, along with pineapples and figs are formed by many flowers fusing together and are called aggregate fruits. By the way, strawberries are not berries, either. They are ripened receptacles. Berries, such as pumpkins, cantaloupes, cucumbers, eggplants, and tomatoes, all have many seeds inside an outer shell of varying thicknesses and hardnesses. Dry fruits, such as peas and beans, grow in pods that either open down a seam (dehiscent), or stay closed (indehiscent), as in the case of peanuts and most cereal grains, such as wheat and barley.
Seeds have three parts: the embryonic plant, stored food, called endosperm, and a protective seed coat. As temperatures rise and moisture is absorbed through the sed coat, a primary root, called the radicle, will emerge, followed by the first stem, or hypocotyl. First leaves, or cotyledons often look very different from adult leaves.
Flowers exist solely to attract pollinators. Only angiosperms make flowers. Gymnosperms, such as conifers, ginkgo trees, and cycads make cones, or strobili. The colors, patterns, showy displays, and sweet aromas we associate with flowers are all in place to attract insects, bats, and birds. Flowers are supported by a stem called a peduncle. Small green leaf-like structure, called sepals, are often seen at the base of a flower. A collection of sepals is called a calyx. Individual petals may produce nectar or scent. All of the petals together are called the corolla. The combined corolla and calyx are called the perianth. The tip of a flower stalk, called the receptacle, contains the plant’s reproductive organs. Flowers can be male, female, or both, though not always at the same time. The female part, or pistil, consists of a pollen-receiving stigma, supportive style, and the ovary. [When you eat saffron, you are eating the style and stigma of an autumn crocus flower.] The male part, or stamen, consists of a pollen-producing anther and a supporting filament. Flowers are very useful in plant identification.
Genetic research and electron microscopes have brought plant anatomy to exciting new levels. Assumptions about kinship have been wrecked asunder and colorized scanning electron microscope (SEM) images can be breathtaking. Different types of plant cells gather together to create tissues. Those tissues come together to create the functional parts of a plant.
Ultimately, all those functional parts grow into delicious, nutritious foods that we can cultivate in our yards for decades. For me, feet up in the yard with a nice glass of wine beats standing in line at a grocery store any day!
What do wedges of citrus, hard walnut shells, the white bits inside a pomegranate, and the paper coating around avocado pits have in common?
They are all endocarps.
How can this be? How can structures so very different be the same part? Let’s find out by starting with some basic fruit facts.
The fruits and seeds we eat are plant ovaries. When a flower is pollinated and fertilized, three new structures form: seeds, pericarp, and placentae. Embryonic seeds attach to the placenta, and pericarp begins to grow, to feed and protect the embryonic seed, and to attract seed-spreading herbivores. There are three different types of pericarp tissue: exocarp (outer skin), mesocarp (flesh), and endocarp (inner layer). So, endocarp is the interior fruit that surrounds seeds. But what about all those differences?
Types of endocarp
Endocarp is generally not fruit in the way you would expect, unless you are talking about peppers or citrus. The fleshy parts of sweet peppers and chili peppers is the endocarp, as are those membranous wedges of fruity goodness found inside lemons, limes, and oranges. If you look inside an apple, the endocarp is the hard clear plate-shaped bits close to the seeds.
If you take a close look at a stone fruit, such as a nectarine or cherry, the endocarp is very hard and inedible. To us, it looks more like the shell of a nut. And guess what? The hard outer shell of walnuts, pecans, and almonds, that shell is the endocarp, even though, to us, it looks as though it is on the outside.
Confused? Read on!
Nuts about endocarp
When a nut develops on a tree, the exterior rarely looks like what you see in the grocery store. Many nut species have smooth or furry green exteriors (exocarp). That exocarp coats a hard, familiar shell. That shell is the endocarp of a nut.
Stamens are the male aspect of a flower.
Flowering plants, or angiosperms, have flowers that can be male, female, or both, though not usually at the same time.
The word stamen comes to us from the Latin word for ‘thread’. This is because the stamen is a threadlike stalk, called a filament, which has a pollen-producing anther on top. The stamen usually surrounds the female part, or pistil, though not always
Different plant families have different arrangements of pistils and stamens. For example:
When eating edible flowers, it is a good idea to remove the stamen and pistils and just eat the petals and other parts. The only exceptions are violas and Johnny-jump-ups. In these cases, the other parts add good flavor. Saffron threads are the dried [female] styles and stigmas of a specific crocus flower species, not the stamen.
Melons, zucchini and other squashes can easily be hand-pollinated by breaking off a pollen-carrying stamen and touching each of the flowers flowers with it.
Now you know.
Basil’s fragrant leaves make it a garden favorite, but there is a new disease on the horizon: basil downy mildew. And warm, moist conditions are all basil downy mildew needs to set up housekeeping on your basil plants.
First seen in Africa, in the 1930’s, basil downy mildew (Peronospora belbahrii) came to the U.S. in 2004 on infected seeds from Italy. By 2008, it had made its way to California and is now a global problem for everyone who enjoys basil and pesto.
Like other downy mildews, basil downy mildew is caused by tiny, algae-like microbes called oomycetes. Oomycetes parasitize vascular plants to complete their life cycle. They do this by collecting on the underside of leaves. From there, these tiny one-celled creatures send out threads that enter the leaf through the stoma and begin propagating. Since the oomycetes cannot pass beyond leaf veins, the damage from each infection is usually contained between leaf veins.
New spores are then released through the stoma, where they fall to soil, waiting to be splashed right back up by rain or irrigation water, or caught on the breeze for a ride to a new host plant. The party responsible for basil downy mildew travels on a variety of surfaces to reach your garden. In addition to water and wind, spores can be carried on garden tools, clothing, transplants, and infected seeds.
So how do you know if your basil plants are infected?
Symptoms of basil downy mildew
Unfortunately, the earliest sign of infection, yellowing leaves, looks a lot like nutritional deficiencies. If you see yellowing between the major leaf veins with dark blotchy areas, take a closer look on the underside of those leaves. If you see purple or gray powdery spores, it is probably basil downy mildew. Those spores are reproductive bodies and each infected leaf is a disease factory.
Once a plant is infected, it is too late. Harvest any healthy leaves and bury the plant under soil or in the compost pile to prevent spores from spreading. Generally speaking, these pathogens will not survive in compost or through winter temperatures. We hope. For now, the basil downy mildew pathogen is under California State quarantine, which means infected plants must be destroyed.
Preventing basil downy mildew
To avoid being part of the problem, be sure to buy only certified disease-free seeds and seedlings, place all new plants in quarantine, and monitor plants closely.
Good air circulation goes a long way toward keeping leaves dry. Dry leaves are not hospitable to this disease, so keep irrigation water at ground level. Skip the watering can. Instead, use a soaker hose or drip system that will prevent spores from splashing up onto the underside of leaves.
At the end of the growing season, cut basil plants off at ground level and compost them completely. Do not leave them in place to harbor disease. This helps break the disease triangle and reduces the chance of things starting up again each spring.
Some research is being done on the effectiveness of spraying basil plants with fixed copper as a preventative, but the results are not yet in.
If you think basil downy mildew has appeared in your garden, please notify your local County Extension Office or Department of Agriculture. You can even use the Basil Downy Mildew Reporting Page to add you contribution to science!
Exquisite nuts or toxic leaves, how much do you know about the cashew family?
Expensive, delicious, and nutritious, cashews (Anacardium occidentale) are treat that you just might be able to grow at home. Before you start planting, however, there is more to the cashew family than meets the eye.
Cashew fruits and nuts
In most cases, these trees, shrubs and vines have female and bisexual flowers while others have male and bisexual flowers. If you want to grow your own, you will probably need two or more plants, with one of each gender.
Did you know that those delicious cashew nuts are not really nuts at all? Instead, they are drupes, much like the pits found in stone fruits, such as almonds, cherries, and peaches. In the same way that those trees, fig trees, strawberries, and pineapples produce accessory fruits, cashew trees do, too. The only difference is that cashew nuts hang underneath their accessory fruits, known as cashew apples. Cashew apples are used to make sweet, astringent drinks and liquor.
If you start taking a cashew drupe apart, you will find that the seed coat is very thin and that there is little or no endosperm, also like a strawberry. [You can think of a seed using endosperm to grow the same way we would use a peanut butter sandwich, while accessory fruits are more like drinking juice - both cases provide nutrition, but in different ways.] Before you try this, be sure to don some rubber gloves. More on that in a minute.
Members of the cashew family
There are hundreds of members of the cashew or sumac family. Along with delicious cashews, the cashew family includes some favorite edibles, and a few you may not have heard of before:
Here, in North American, smooth sumac (Rhus glabra) and stag horn sumac (R. typhina) are used to make a drink called “sumac-ade”. The cashew family also includes mastic trees (Pistacia lentiscus) and varnish trees (Toxicodendron vernicifluum), which are the trees that give us varnish, lacquer, and useful oils. Natural varnish is made from tree resin.
Like many other families, there is heated debate about who belongs and who does not. Not too long ago, pistachio plants were brought into the cashew fold, but there are still discussions about this in scientific corners. Cashew family taxonomy includes dozens of genera, most of which are not edible. Watch out, though - some of them might try to hurt you!
Cashews - beware!
Did you know that raw cashews are poisonous? They are. They contain the same chemical found in poison ivy, poison oak, and poison sumac. That’s because they are all in the same family! The sap of all cashew family plants, called urushiol, is something to be reckoned with as it can be highly toxic. Just under the bark, these plants have resin canals filled with the stuff.
If that weren’t bad enough, the seed coat of cashew drupes contains a toxic oil that is acidic enough to burn your skin. If you are still interested in growing your own cashews, read on. If not, read on anyway! Who knows what you’ll learn?
How to grow cashews
Being native to tropical and subtropical places such as India, Thailand, Sri Lanka, and Papua New Guinea, cashew tree might be difficult to grow, depending on your Hardiness Zone. If you are determined, however, it can be done. Keep in mind, before you get started, that mature, full-sized cashew trees can grow to nearly 50 feet in height. Dwarf varieties are far more manageable at only 20 feet.
Cashew trees prefer loose, sandy soil with plenty of sun and excellent drainage. Do not try using grocery store seeds - they are not viable. You will need to get seeds from a reputable supplier. Viable seeds should be planted 4 inches deep and about 30 feet away from each other. These plants can handle temperatures as high as 122°F, but cold and damp will be the death of them. Heavy, soggy clay soil nearly always causes root rot in cashew trees. They don’t handle wind very well, either, so be sure to provide tree supports while trees are young and do not plant them in windy areas.
Keep your young tree properly irrigated and feed trees twice a year using a mix determined appropriate by your soil test results. Generally speaking, cashew trees use a lot of nitrogen, phosphorus, and zinc. After 3 or 4 years, you should be able to harvest your first crop of cashews. You will know your crop is ready to harvest when the cashew apple is either red or yellow and the drupe shell has turned grey.
Before you start nibbling, however, remember that the seed coat of cashew drupes contains a toxic oil. You will need to roast those nuts in a covered container at 375°F for 10 to 20 minutes. Traditionally, they are roasted covered in sand. Apparently, the toxins released as fumes during this process will ruin your cookie sheet or whatever lid you opted for, so choose accordingly and be sure to ventilate the area as you work. Since the oils within cashew shells is extremely acidic, it can burn your skin, so wear long sleeves and eye protection.
Next, shake the nuts in a sieve, if they were roasted in sand, and then wash them in soapy water to remove any residual toxins. Crack open your priceless cashews now and use a knife to remove the thin seed hull. Finally, saute your cashews in oil at 300°F for 5 minutes or so to neutralize any last bits of toxins.
Did you know that cashew shells have been used to make lubricants, paint, and military arms?
I didn’t either.
I think I’m beginning to understand why cashews are so expensive…
For anyone unlucky enough to have a chance meeting with poison ivy (Toxicodendron radicans), Pacific poison oak (T. pubescens), Atlantic poison oak (T. diversilobum), or poison sumac (T. vernix), you know all too well how those plants can make you devastatingly uncomfortable. Believe me, I speak from experience.
"Leaves of three, let it be; berries white, take flight; root hairs red, recoil"
[I made up that last bit.]
Sweet alyssum is a lovely, low maintenance flower that attracts butterflies, but it isn’t actually an Alyssum.
Not so long ago, when scientists first started using DNA to sort out plant species and plant families, a number of embarrassing relations and non-relations were discovered. This has lead to upheaval in the world of plant nomenclature. While this doesn’t generally affect us, as backyard gardeners, it can cause some confusion when it comes to plant names. So it is with sweet alyssum.
Native to the Mediterranean region, dainty sweet alyssum used to be counted among the Alyssum species. As such, it was known botanically as Alyssum maritima. [Isn't that a lovely name?] We now know that the global sweet alyssum plant is actually a Lobularia species, an equally pleasant name.. Again, this doesn’t make much of a difference for us, as home gardeners. What I was surprised to learn is that, in both cases, sweet alyssum is a member of the cabbage family, which means that it might attract the same pests and diseases as your cabbages, broccoli, and mustards. Before we start ripping out this tiny, durable flower, let’s see what it has to offer.
Sweet alyssum description
Each sweet alyssum plant grows up to 12” tall and wide. Stems are made up of several branches, each of which has many flower clusters. Most sweet alyssum flowers are white, but you may get an occasional blue, pink, or purple in the mix. These flowers have a honey sweet aroma that bees and other pollinators seem to love. As individual stems near the end of their life, a profusion of fruits, which are hairy elongated pods, like most other members of the cabbage family. Each pod contains two seeds. These seeds spread easily on the wind. And plants can thrive in a number of different locations.
How to grow sweet alyssum
Sweet alyssum somehow manages to grow in rocky outcrops, on sand dunes, between paving stones, and everywhere else seeds can get a toehold. This is good news. Unlike their perennial Alyssum cousins, sweet alyssum is an annual. If you have it growing already, you know that it readily self seeds.
Sweet alyssum is an excellent choice for softening paths, lining the edges of raised beds, or as a relatively maintenance-free ground cover. I say ‘relatively’ because sweet alyssum plants may get leggy and flop over near the end of their productive lives, leaving them to look somewhat less appealing. You can eliminate this look, and stimulate new flower growth, by occasionally giving plants a trim. I use my weedwacker.
Sweet alyssum pests and diseases
As far as cabbage family members go, sweet alyssum is rugged. It has very few problems. Diseases that may impact your sweet alyssum include botrytis blight (grey mold), clubroot, downy mildews, fasciation, and root and crown rots, though I have never seen any of those diseases on my sweet alyssum while the same diseases have, at times, been present on nearby plants. Supposedly, the cyclamen mite and caterpillars of the diamondback moth feed on sweet alyssum. Again, I have not seen this in my garden. The only pest that I have seen hiding out, under the canopy of sweet alyssum blossoms is the dreaded Bagrada bug.
Rather than ripping out your sweet alyssum, just trim it back every once in a while and be sure to take a peek underneath its skirts every once in a while, with an eye for Bagrada bugs.
What do peaches and potatoes have in common? The green peach aphid.
Considered the world’s worst disease vector among garden plants, green peach aphids (Myzus persicae) love to feed on peach and potato leaves, along with dozens of other garden plants.
Green peach aphid description
Green peach aphids are generally found in colonies of winged and wingless adults and immature nymphs. Green potato aphids look a lot like potato aphids (Macrosiphum euphorbiae). While potato aphids can be seen throughout the plant, green peach aphids prefer hiding on the underside of leaves.
Damage caused by green peach aphids
Green peach aphids often overwinter in the egg stage on stone fruits, particularly on peach and peach hybrids, though apricot and plum are also favored. In spring, these eggs hatch and nymphs begin feeding on buds, flowers, and new stems. A few generations later, which only takes a month or so, winged adults move to summer feeding areas. It would probably be simpler to list the garden plants that do not attract green peach aphids, but you do need to know where to look for these pests.
Summer feeding can occur on artichoke, asparagus, beans, beets, broccoli, Brussels sprouts, cabbage, carrot, cauliflower, cantaloupe, celery, chili peppers, corn, cucumber, fennel, kale, kohlrabi, turnip, eggplant, lettuce, mustard, okra, parsley, parsnip, peas, peppers, potato, pumpkin, radish, spinach, squash, sunflowers, tomatoes, turnips, watercress, and watermelon.
Aphids prefer feeding on tender new growth. This leads to wilting, water-stress, and stunting. It also generates a lot of honeydew (sugary insect poop), which provides the perfect growth medium for sooty mold. Heavy aphid feeding can weaken a plant to the point of death. The bigger problem, as with nearly all aphid species, is that these pests carry diseases. Green peach aphids may infect plants with a variety of viral diseases, including:
If potato leafroll virus appears in your garden, it is a good idea to remove the infected plant, plus three other plants in every direction, to prevent green peach aphids from spreading the disease even further. This is yet another reason why it is so important to plant certified disease-free plants in the first place. These pests are often found in greenhouses, so placing new plants in quarantine can go a long way toward preventing an infestation. They can also travel on the wind, so it's a constant battle.
Green peach aphid management
The best way to control green peach aphids is to hit them in winter. This means removing overwintering sites, such as infested leaves, spent plant debris, and nearby weeds. Malva is a popular winter wonderland for aphids, so keep that weed away from your peach trees and potato plants. Bindweed, lambsquarters, penny cress, pigweed, sowthistle, tumbleweeds, white goosefoot, and rouge members of the nightshade family can also provide overwintering sites for this pest.
As spring and summer come around, however, you can attract and protect beneficial predators, such as lady bugs, lacewings, parasitic wasps, and syrphid flies, by providing fresh water, planting a variety of insectary plants, and avoiding the use of broad spectrum pesticides. Most chemicals designed to kill aphids cause more harm than help by disrupting the lifecycle of many natural predators. There is also a parasitic fungus (Entomophthora aphidis) that attacks aphids, but you can’t do anything about that one.
Early each June, in northern California, green peach aphids migrate into our gardens. You can prevent a full-blown infestation by monitoring plants on a weekly basis and using a damp rag or paper towel to wipe off colonies before they can really start propagating. A single female, hatched in spring, can reach sexual maturity in only 10 days, creating 20 generations in a single year. By the end of summer, this can result in billions of offspring.
Bacterial brown spot is a bacterial disease that causes brown spots on beans, lentils, and other legumes.
The bacterium responsible for bacterial brown spot is called Pseudomonas syringae pv. syringae. This bacteria is already found on the leaves of many different plants. Wind, rain, overhead watering, or coming into contact with infected seeds and plants can cause bacterial population explosions in snap beans, pole beans, peas, lima beans, and other legumes. Bacterial brown spot can also infect orchids, so be sure to wash your hands and sanitize your tools.
The pathogen enters through stoma and points of injury, usually when temperatures are below 85°F, and during the rainy season. Before long, symptoms will appear.
Bacterial brown spot symptoms
Bacterial brown spot is frequently confused with halo blight and common blight. In all three cases, small, water-soaked lesions appear on leaves. In common blight, those lesions have wide, lemon-colored borders, and they continue to grow. Halo blight lesions tend to stay small and they have prominent light green halos, hence the name. Bacterial brown spot lesions have narrow light green borders and the centers tend to dry out and look tattered. The spots may overlap, creating an even more tattered appearance. Pods infected with bacterial brown spot become distorted. Lesions are also seen on stems.
These lesions interfere with photosynthesis, weakening plants and reducing your crop. Rather than allowing infection to spread, it is better to remove infected plants and toss them in the trash.
Preventing bacterial brown spot
Start out with certified disease-free plants and seeds. If you buy plants, put them in quarantine until you are certain that they are healthy.
Overhead watering spreads bacterial brown spot infections, plus it provides the bacteria with needed moisture, so don’t do it. Use soaker hoses, drip lines, or simply hold your garden hose closer to the ground as you water.
At the end of the growing season, remove host plant debris and add it to the compost pile. Crop rotation and fixed copper sprays can also reduce the risk of bacterial brown spot.
Mottles are symptoms of viral disease. Mottles are irregularly colored, spotted, or blotched areas. These discolored areas are usually yellow. Simple, right? Well, those words also describe mosaic diseases, which are different from mottles. I think.
Note: Have you ever started something, thinking it would be simple, and come to find out that there is a lot more to it than you ever would have thought? Mottles are like that.
There are several families of viruses that cause mottle diseases in plants. They cause mosaic diseases, too. And each of these families causes dozens, maybe hundreds, of diseases. I had no idea. There are even sub-viral agents, which lack the genetic instructions needed for replication. Because of this, they use helper viruses to set up household in plant victims. I swear, the more I learn, the stranger the world gets.
There are countless plant diseases that present with mottles, including:
What I have learned is that mosaic patterns tend to be dark green on green, yellow on green, or gold on green, with either distinct or fuzzy borders, and in systematic patterns. Mosaic diseases may also appear with vein banding, stripes, streaks, and variegation.
Mottles, on the other hand… well, um, well, mottles can look exactly like mosaic diseases, but without the variegation, banding, or stripes. Rats! The only information I could find was that mottles can also appear on fruit, while mosaics tend to be seen only on leaves. I think. And then there are diseases like cucumber green mottle mosaic and soybean yellow mottle mosaic virus. Agh!!!
If you think the first photo looks exactly like this photo, you would be correct. Apparently, even the experts haven't sorted all this out yet, so don't feel as though you should understand it all. I certainly don't!
Maybe mottles and mosaics are the same thing after all. If you know the answer, please share it with the rest of us in the comments.
Bottom line, if you see uncharacteristic coloration on leaves or fruit, you need to take a closer look and consider what might be causing it before a full blown infection wipes out your crop.
Armillaria root rot is a soil borne that attacks the roots and trunks of many fruit and nut trees. It is also the largest living fungi in the world.
In Oregon’s Malheur National Forest, there is a mushroom colony that covers 2.200 acres. That colony is believed to be a single entity, all growing from the same network of fungal mycelium.
By itself, that's impressive. In your tree, it's a deadly fungal disease.
Trees vulnerable to Armillaria root rot
Also known as honey fungus, shoestring fungus, or oak root fungus, Armillaria root rot (Armillaria mellea) is a deadly disease that infects avocado, cherimoya, cherry, chestnuts, conifers, kiwifruit, kumquat, lemons and other citrus, pomegranate, stone pine, and walnuts, along with the mighty oak. If that weren’t bad enough, trees weakened by Armillaria root rot become more susceptible to serious pests, such as Pacific flathead borers.
Armillaria root rot symptoms
Everything starts out looking fine. Your tree is growing nicely and you suspect nothing. Suddenly, you notice downward cupping leaves, chlorosis (yellowing), dieback of upper limbs, and leaf drop. You may also see a variety of mushrooms growing nearby.
Your tree is dying. Young trees die quickly, while older trees make take longer, but the end result is nearly always the same.
Armillaria root rot diagnosis
If your tree shows the above mentioned symptoms, take a closer look at the base of your tree. You may be able to see fan-shaped fungal growth rising up the trunk from the soil level. Use a sharp knife and cut away a section of bark at the base of the tree, so you can see the cambium layer. If you see white fungal threads (mycelia) and can smell a strong mushroom odor, your tree is in serious trouble. If you see reddish brown streaks or patches, or water-soaked areas, the infection is more likely to be Phytophthora root and crown rot, rather than Armillaria, though that isn't any better news for your tree.
If you have easy access to the tree’s roots, cut one open. Infected roots are darker than normal and have a cottony center. You may also see black rhizomorphs, called ‘shoestrings’, on the surface of infected roots.
How Armillaria spreads
As a soil borne disease, Armillaria mycelia can remain viable in the soil for many years. It isn’t until a healthy root comes into contact with infected wood, roots, stumps, or other wood fragments. Then, the fungus enters the healthy tree and begins to populate the cambium layer, eventually killing the tree. Infected nursery stock can also carry this disease, so always quarantine new plants.
Preventing Armillaria root rot
Good drainage, sunburn protection, and proper (not excessive) irrigation can all help protect your trees against Armillaria root rot. Once infection occurs, the tree should be completely removed and the area should only be planted with crops that are not vulnerable to Alternaria root rot.
Dark brown spots on your tomatoes? It’s probably early blight.
Cool spring temperatures and too much rain or other moisture creates the perfect storm for this fungal disease. The early blight fungus (Alternaria solani) is a disease of the nightshade family, which means your potatoes, eggplants, bell peppers, and chili peppers are equally susceptible, as are other plants in the nightshade family, such as petunias and blue potato bushes. If similar lesions are seen later in the season, it is more likely to be late blight, also known as the dreaded potato blight.
Early blight was once a disease found only on the east side of the Rocky Mountains. Sadly, that is no longer the case. The early blight pathogen is now found everywhere host plants have been grown and can result in up to 30% of your potatoes and 79% of your tomato crop ending up in the trash bin.
Early blight symptoms
Small black or brown spots, usually 1/4 to 1/2 inch in diameter, may appear on fruit, leaves, and stems. These spots may have a concentric rings pattern, or bullseye. Fruit spots are dry, sunken areas, most commonly seen near the calyx end of the fruit. [That’s the flower end, as opposed to the stem end.] Spots on leaves feel leathery. Symptoms are seen on older leaves first. Stem lesions do not have the same circular, bullseye pattern.
In some cases, this pathogen can cause collar rot and damping off, which usually kills seedlings. As the disease progresses, leaf loss can significantly reduce fruit production. Honestly, the fruit that is produced doesn’t look particularly appetizing. Infected potatoes either rot in the ground or in storage.
Early blight lifecycle
Fungal spores overwinter in the soil and on infected fruit and plant debris. Rain and overhead irrigation splash spores onto plants, where they begin reproducing. To reduce the chance of early blight in your garden:
Fixed copper or sulfur sprays can provide fungicidal benefits in heavy infestations. Also, healthy plants are less likely to become infected, so feed and water your plants properly, give them enough space to reach full size, and help them avoid physical injuries, which provide entry points for early blight fungal spores.
Are your strawberry plants looking pitiful? Do they fail to produce big, luscious fruits? It may be virus decline. [And those berries are not really berries, they are accessory fruits, but I digress.]
Virus decline is a combination of multiple viral infections that leave strawberry plants looking like they’ve missed too many meals.
Causes of virus decline
Virus decline is a combination of viruses: Strawberry pallidosis associated virus (SPaV) or Beet pseudo yellows virus (BPYV), both which are spread by whiteflies, combined with any one of several other viruses commonly spread by aphids. Because virus decline is a combination of infections, plants may look fine one day, even though they’ve already been infected by SPaV or BPYV, and then look bad a few days later, having become infected with another of the relevant viruses. These aphid-borne viruses include:
Strawberry latent ringspot and Fragaria chiloensis latent viruses may also play a role. Research is currently underway.
Virus decline symtoms
Plants infected with virus decline are often stunted, sometimes severely. Leaves turn purple or red, though new growth that forms near the center of the plant may remain green. There is little or no fruit production, and the roots are brittle and reduced. These plants will never be productive.
Control of virus decline
You cannot know for sure if your strawberry plants have virus decline without sending a sample in for lab testing (which your County Agriculture Office may offer for free). but declining plants are best removed and replaced, preferably in a new location.
One way you can reduce the likelihood of virus decline occurring in your strawberry patch is to keep other plants that might host these viruses at a safe distance. The SPaV virus favors strawberries and its cousins, and a few weeds, such as nettle, creeping sibbaldia, mock strawberry, sharp leaf groundcherry, and cheeseweed. BPYV, however, has a taste for your melons, squashes, lettuces, cucumbers, endive, and spinach, along with marigolds, zinnia, dandelions, and cheeseweed.
To reduce the possibility of virus decline in your strawberries:
These steps are no guarantee, but they will significantly reduce the chance of your plants becoming infected.
Two-spotted spider mites can kill off many of your garden plants as temperatures rise and humidity drops. Before a hot, dry summer kicks in, it’s a good idea to know what to look for.
Two-spotted spider mites (Tetranychus urticae) can become a serious threat to your citrus and other fruit trees, most vegetables, and many ornamentals, such as marigolds, roses, and salvia. Beans, blackberries, blueberries, cucumber, eggplant, lettuce, peas, squash, strawberries, and tomatoes are all favorite foods of the two-spotted spider mite.
Two-spotted spider mite description
As arachnids, all mites have two body segments and eight legs. Two-spotted spider mite eggs are round to spherical, but very difficult to see. Instead, you may see the webbing used to protect those eggs. Colorless larvae, which start out with only six legs, go through two developmental stages to reach greenish-yellow, eight-legged adulthood. This transformation can occur in as little as 5 days, and females can lay 120 eggs in their lifetime, so populations can rapidly explode.
An interesting note, unfertilized eggs hatch into males, while fertilized eggs hatch as females. This is called arrhenotoky.
Males are smaller and have narrower bodies and are more active than females. These close cousins to red mites are greenish-yellow to brown, with two dark spots, and they even have a red winter phase, but you probably won’t be able to see them without a hand lens. [Those dark spots are accumulated body wastes, so they are not always visible.] At only 1/50” long, two-spotted spider mites are easier to find by looking at the damage they cause.
Damage caused by two-spotted spider mites
As sap-sucking pests, similar to citrus mealybugs and citrus bud mites, these mites pierce plant cells and remove the contents. Hidden from view by feeding on the underside of leaves, they often go unnoticed until the damage becomes obvious. Mite feeding causes stippling and bleaching. These damaged areas increase, causing bronzing and early leaf drop. If you look at the underside of these leaves, you will often see the cast-off exoskeletons of mites. You may also see extensive webbing over buds, stems and flowers. Extensive feeding can cause stunting and even plant death.
How to manage two-spotted spider mites
Since two-spotted spider mites feed on such a wide range of plants, they are difficult to control. Mites favor feeding on stressed plants, so proper feeding and irrigation can help your plants seem less appealing to these pests. In addition, you can use these tips to reduce problems caused by two-spotted spider mites:
Predatory mites, such as Phytoseiulus persimilis, ladybugs, minute pirate bugs, and lacewings are all beneficial insects that feed on two-spotted spider mites, so keep you yard hospitable to these helpful predators. Mites are developing resistance to most chemical pesticides, but insecticidal soaps are effective against mites, with horticultural oils (not dormant oils) coming in a close second. These treatments are only affective against the mites that come into contact with it, so repeat treatments are often necessary.
The ashy grey lady beetle is both stylish and deadly.
We’ve all seen the red domed lady bugs of popular culture, with their shiny black dots, but what about the black lady beetles with red dots?
There are only four types of black lady beetles with red spots. The twicestabbed lady beetle (Chilocorus orbus), Axion plagiatum, Chilocorus kuwanae, and the ashy grey (Olla v-nigrum). Unlike other lady beetles, however, the ashy grey comes in two forms: dark and tan, which can be changed at will!
Ashy grey lady beetle description
Ashy grey lady beetles are sometimes ashy grey or tan, with black spots. At other times, they are black with red spots. Before they reach their domed adulthood, ashy grey lady beetles look more like tiny alligators with yellow spots.
And before that, as pupae, they look like little orangish-yellow nubs. As eggs, they look like clusters of yellow, usually found on the underside of leaves, close to prey.
Ashy grey lady beetle prey
While ashy grey lady beetles do feed on the eggs of butterflies and moths, the lion’s share of their diet consists of aphids and psyllids. Since aphids and psyllids are both disease-carrying, plant-sucking pests, we can use as many lady beetles as we can get in the garden.
To attract ashy grey lady beetles and other beneficial insects to your yard, avoid using broad spectrum pesticides, provide fresh, clean water, and plant a variety of insectary plants, such as dill, lavender, chives, mint, tansy, and yarrow, just to name a few.
How many different types of lady beetles are in your garden?
The soil food web is what makes it possible for plants to grow.
Soil is not simply ground up minerals. We now know that there are gazillions of living things breathing, growing, moving, and reproducing beneath our feet.
The living things found in soil are mostly smaller than you can see, with only a few exceptions. As these tiny life forms move through the soil, they reduce erosion, impact water and nutrient availability, and aid in decomposition of manure, plants, and pesticides.
Algae are single-celled organisms that can form substantial chains. Algae are classified by color. [Did you know that kelp is a type of algae? I didn’t either.] Algae convert sunlight into energy through photosynthesis. They can also fix atmospheric nitrogen. There may be 10,000 to 100,000 algae in a teaspoon of soil. Algae aid in nutrient cycling and help prevent erosion.
Arthropods are bugs. Bugs do not have backbones. Instead, they have exoskeletons. Arthropods include insects, crustaceans, and arachnids. Common insects include ants, beetles, and springtails, while sowbugs are crustaceans. The arachnids include spiders, mites, and millipedes. Arthropods eat a variety of foods. Some types feed on fungi, while others prey upon worms and other arthropods, and yet others are herbivores. As they feed, arthropods aerate the soil, aid in decomposition, and keep other populations in check. At the same time, arthropods can damage root systems.
Bacteria are one-celled organisms. They are so tiny that they can enter a plant through a broken hair, or trichome. It is estimated that there is one ton of bacteria in every acre of soil. That’s the weight of two adult cows, or half of your car. A teaspoon of productive soil may contain anywhere between 100 million and 1 billion bacteria.
Most bacteria are decomposers that prefer more tender fare. As they breakdown carbon-based life forms, they make those nutrients available to plants and improve soil structure. Other bacteria are mutualists, which means they work together with plants to everyone’s benefit. This group includes the bacteria which convert atmospheric nitrogen into a form available to plants. Another group of bacteria, called lithotrophs, break down hydrogen, iron, nitrogen, and sulfur compounds, rather than carbon, making those nutrients available to plants. The fourth group of bacteria are pathogens. This group includes Erwinia (fireblight) and Xymomonas diseases, and gall-forming Agrobacterium.
Recent research has shown that a certain soil bacteria, Mycobacterium vaccae, improves mood and reduces stress. See, gardening really is good for you!
Earthworms are popular decomposers, improving soil structure as they feed on organic matter and move through the soil. Earthworm poop, or casts, is a fermented batch of plant material, bacteria, and fungi that forms nutrient-rich soil aggregates. Earthworms improve soil structure, porosity, infiltration and drainage, as well as make life a lot easier for plant roots. Earthworms are also credited with reducing erosion and runoff.
Fungi are single and multi-celled organisms that grow as long threads, called hyphae. Those hyphae may cluster into groups called mycelium. Yeast is a fungi. So are mushrooms and dog vomit mold. Fungi help bind soil particles together, improving soil water holding capacity and infiltration rates. Most fungi, called saprophytic fungi, are important decomposers that can break down harder materials than bacteria can, such as tree trimmings, and hold those nutrients in the soil, rather than allowing them to be lost to the atmosphere through erosion and runoff.
Other fungi (mycorrhizae) are mutualists that live on and in plant roots, bringing soluble nutrients to your plants. Plant roots can only come into direct contact with approximately 2% of the surrounding soil. With the aid of fungal threads (hyphae), those roots then have access to all the water and nutrients found in 20% of the soil. There are pathogenic fungi, such as Pythium, which cause blackleg, seed rot, and cavity spot, Rhitozoctonia, and Verticillium, which cause Verticillium wilt, among others. Parasitic fungi feed on insects and nematodes.
Nematodes are worms without segments. Some are large enough to see, at 1/20”, but most are smaller than that. We know surprisingly little about beneficial nematodes. Most research has focused on root feeding omnivores that parasitize our plants. In the world of nematodes, life is hard. There are nematodes that feed on bacteria, fungi, and other nematodes and protozoa, while those same creatures prey upon and parasitize the nematodes. This whole process can either spread or control disease, depending on who wins that particular fight. Nematodes benefit plants by releasing excess nitrogen into the soil, like protozoa. As bacterial and fungal feeders, nematodes keep those populations in check while, at the same time, expanding their ranges by carrying microbes with them. There are usually 100 nematodes per teaspoon of soil.
Protozoa are one-celled organisms that feed on bacteria, fungi, other protozoa, and plant material. These opportunist feeders are significantly larger than bacteria, but you still can’t see them. As they feed, protozoa are unable to digest all the nitrogen in their prey, so they pee it out, releasing nitrogen into the nearby soil in the form of ammonia (NH4+), which plants love to consume.
Small animals, such as gophers, moles, rabbits, snakes, and voles are the giants of this microscopic world. As amphibians, birds, mammals, and reptiles scratch at and burrow through the soil, they help reduce compaction. They can also destroy plant roots. While both predators and prey aid in nutrient cycling, some are more beneficial to your garden than others. In my opinion, snakes, lizards, and toads are preferable. That’s just me.
Bottom line, like any other food web, everything gets eaten by something else. Your soil is no different. As things are eaten, the elements that make them up get broken down into smaller bits. These smaller bits get eaten by something else until, ultimately, plant roots absorb those nutrients to help them grow.
The Earth’s crust is a living, breathing entity whose health dictates our own. Do right by your soil, and your garden will thrive. The greater biodiversity in your soil, the healthier we will be.
If you have access to a microscope, I urge you to collect some samples of your garden soil and take a closer look at what is supporting life in your yard. What life forms can you see in your soil?
How would you like to transform your soil from compacted concrete (or lifeless sand) for free?
You can, with tree trimmings!
Tree trimmings, also known as arborist chips or Tahoe chips, consist of coarse, medium, and fine wood chips, pine needles, twigs, leaves, and bark. It isn’t the pretty, uniform stuff you buy in bags from the garden center. This is what’s left over after a hard day’s work of trimming trees.
Professional arborists chip everything they cut off a tree into bits. These tree trimmings either go to a landfill or civic composting center, for a fee, or to someone’s driveway, for free.
Benefits of mulching with tree trimmings
Tree trimmings make an ideal mulch. The green leaves and new buds break down quickly, while medium-sized twigs and stems break down a little more slowly. Coarser pieces take longer to breakdown. This process creates a time-release of nutrients and organic material that provide a wealth of benefits, including:
But, what about toxins or disease? Let’s learn the truth.
Toxic wood chips
You have probably heard rumors about the way certain types of wood chips are toxic to garden plants, preventing germination or killing them outright. In nature, this form of chemical warfare is called allelopathy and black walnut is usually the first to come to mind. It is true that black walnut trees produce a compound, called juglone, that can kill off competitors. But juglone only affects some shallow-rooted plants and black walnut is too valuable as lumber to end up chipped. Other commonly accused chips include cedar, redwood, and Douglas fir, but there has been zero scientific proof that trimmings from these trees negatively affects other plants. They do, however, inhibit some fungi and bacteria, and repel or kill clothes moths, termites, cockroaches, ants, and carpet beetles.
What to look out for
Before accepting a load of wood chips from your local arborist, be sure to ask if the load contains any palm tree trimmings. New palm trees can grow from these pieces. This is not what you want in your garden. Believe me. Here in California, we call palm trees ‘rat hotels’ for good reason. If the load contains palm tree, let it go somewhere else.
Many people are concerned about diseases and pests being transferred through tree trimming loads. For the most part, this fear is unwarranted. In nearly all studies, pathogens such as Verticillium, Cytospora, Thyronectria, were found unable to move from the mulch layer, into and through the soil to plant roots. They simply couldn’t do it. So don’t worry about tree trimmings bringing disease to your landscape, unless you make the mistake of digging the chips into the soil. It is far better to just dump them on top of the soil and let nature do all the work.
[Note, most pathogens are already present. They become a problem when plants become unhealthy enough to be susceptible. Mulching with tree trimmings helps your soil and plants be healthier, and less prone to disease.]
Speaking of work, moving wheelbarrows full of tree trimmings from your driveway to your landscape is work. It’s not backbreaking, but be sure to wear sunscreen, a hat, and gloves. You can skip the gym.
Tree trimmings and nitrogen loss
As mulch of any type breaks down, the microorganisms responsible for decomposition consume nitrogen. This makes nitrogen temporarily less available to nearby plants for 6 to 8 weeks. This is only true for the most shallow-rooted plants and has no effect on deep-rooted, established plants. You may need to add a little extra nitrogen during this time if you apply tree trimmings near vegetable plants. In the long term, as the wood continues to break down, it will add nitrogen and other nutrients to the soil.
And if you happen to see white fungal threads spreading through your tree trimmings, fear not! These fungi are a blessing to your soil and should be celebrated for the good health they bring to your plants.
Tree trimmings and fire safety
Some mulches are more flammable than others. If you want to improve soil structure, retain moisture, and reduce weeds, tree trimmings are your best choice. A group of fire and gardening professionals got together in Nevada to test various types of mulch for fire safety. The material you are most likely to get from an arborist is rated with moderate flames and spread, compared to shredded rubber, which burns the hottest (630°F) and flames the highest (over 3 feet), and composted wood chips, which is the only material that did not “demonstrate active flaming combustion”. So, as your tree trimmings break down, they will go from low risk to no risk.
How to get tree trimmings
Most arborists are happy to give away full or partial truckloads of perfectly good mulch. Simply give them a call and let them know you are interested. They will put your name on a list and call you when they have a load available. Then, park your car somewhere else for a few days and get ready to transform your landscape!
And be sure to gift your friendly, neighborhood arborist with the fruits of your garden labor. You will want another load in a few years!
Spread those tree trimmings 4 to 6 inches thick and let the magic happen. As always, keep mulch several inches away from trunks and stems to avoid diseases, such as crown rot.
Now, go call your local arborist!
Rove beetles are a family of mostly elongated predators that protect your plants against a great many garden pests.
There are over 63,000 different species of rove beetles (Staphylinidae), making them the largest beetle family in the world. There are approximately 4,360 species in the United States. Rove beetles have been around for over 200 million years and it may take another 200 million years to sort out this particular family tree. Currently, there are over 30 subfamilies of rove beetle, and scientists are still trying to sort it out.
However these tiny beetles end up being related, the majority of them pack a wallop when it comes to devouring many common garden pests.
Also known as trash beetles, these beneficial insects are often found in leaf litter, mulch, under loose bark, and around fallen trees. They may also be found in bird nests and rodent burrows where they presumably feed on fly and flea larvae. This huge family is extremely diverse. Some have evolved to live within caves, while others prefer living in mushrooms.
Rove beetle description
As you might expect from a family of this size, rove beetles come in a variety of shapes and sizes. Most of them are very small, averaging only 0.08 to 0.30 inches long, but they can range from 0.03 to 1.5 inches in length.
Most rove beetles have a narrow body that can squeeze into tiny crevices in search of prey and shelter. Rove beetles can be black to brown, yellow to red, and even an iridescent blue-green. They have thread-like antennae with 11 segments; some of them have little knobs at the ends. Most rove beetles have short wing covers (elytra), which means you can see several abdominal segments. Many rove beetles look like a multicolored earwig without its pincers, but certainly not all.
Rove beetle eggs are typically white, but can be spherical, pear-shaped or oval. Flattened larvae may have a distinct ‘neck’ or an armored head, though not all exhibit those characteristics. Pupae can be hard, dark colored cases, or naked white grubs, depending on the species. Adults tend to be long-lived.
Many rove beetle species produce secretions. Some of these secretions help repel water, allowing clumsy insects to recover from falling into water, while other secretions can be particularly toxic. One of those toxic secretions, found in the Paederous group, is transferred from mother to offspring, at birth, providing protection against spiders. This secretion can cause skin irritation and it can damage your eyes. It is the most powerful animal toxin that we know of, but scientists are learning how to use it to heal lesions and treat cancer.
Rove beetle diet
Adult rove beetles eat mites and small insects, as well as root maggot eggs and larvae. Rove beetle larvae also parasitize root maggot larvae. The rove beetle diet is a Who’s Who of garden pests, including:
If eating all those pests weren’t reason enough to appreciate rove beetles, it ends up that adult rove beetles also pollinate cherimoya fruit.
You can help the rove beetles in your garden by avoiding the use of broad-spectrum pesticides and insecticides, and by maintaining permanent areas planted with bunch grasses or other low-growing perennials to provide year-round habitat for these tiny hunters.
What types of rove beetles have you seen in your garden?
Get your beans growing skyward with a tuteur.
Tuteur is French for ‘trainer’ and pronounced the same as that tutor who helped you through middle school algebra.
What is a tuteur?
Tuteurs are 3- or 4-legged obelisk-shaped trellises used to provide a climbing structure for peas and pole beans and other climbing plants. Actually, a tuteur can have as many legs as you like, as long as it is sturdy enough to not topple over.
Traditionally, tuteurs were nothing more than a handful of branches lashed together at the top and spread apart at the bottom, teepee-style. Placed over young pea and pole bean plants, these structures provided supports for young tendrils to wrap around as they climb toward sunlight.
Like other forms of vertical gardening, tuteurs take up less space while expanding your growing options. They also reduce pod exposure to fungal spores and slugs and snails, and they create interesting focal points in your garden.
While you can certainly buy a tuteur, they are very easy to make and odds are good that you already have all the materials you need to make one for free.
How to make a tuteur
At its most basic level, a tuteur can be nothing more than 4 long poles lashed together near the top, with the legs spread out at the bottom. At the other end of the design spectrum, you can construct an ornate obelisk, complete with gazing globes, wind chime, or whatever strikes your fancy. Whatever design you choose, keep in mind that some plants can become substantial, so you will want your tuteur to be sturdy enough to handle whatever will be using it for support. Of course, once the tendrils do all their winding and climbing, they will add a measure of stability to whatever structure they climb.
To create a simple tuteur, you can use bamboo poles, scrap untreated lumber, tree branches, rebar, and many other reusable materials, following these steps:
I threw this one together in less than 10 minutes, using old bamboo poles and some twist ties. It isn’t strong enough for anything heavier than peas and beans, but it’s handy and can be taken apart easily at the end of the growing season.
If your tuteur is sturdy enough, you can also use it to grow cucumbers, squash, and melons. If your crop is particularly large, you may want to provide some extra support, in the form of a hammock.
If you want to get really fancy, you can weave vines or willow boughs into your tuteur to provide extra toeholds for tendrils, while creating an artistic look. There are many online instructions for tuteurs, so try making one for your garden today!
Vinegar makes for great pickles and salad dressings, but can it kill weeds? Let’s find out!
We’ve all heard the story - spray your weeds with vinegar and they die. What a great idea! And so easy! But does it really work? First, let’s learn a little bit about vinegar.
What is vinegar?
You know it when you smell it or taste it. There is no mistaking the tang of vinegar, or the smell of decorating Easter eggs. Vinegar is a sour, acidic liquid made from fermented low-alcohol liquids, such as beer, wine, or cider. The acid in vinegar is called acetic acid. The vinegar you buy in the grocery store is 95% water and 5% acetic acid. When the concentration is 8% or higher, it must be labeled acetic acid. Some people call this higher concentration horticultural vinegar, but I find that label misleading. It is not vinegar. Vinegar is food, while acetic acid is a potentially dangerous chemical. The difference between the two matters.
Acetic acid as herbicide
To be used as an herbicide, commercial agriculture uses a 20% concentration of acetic acid while wearing protective clothing. Acetic acid is a contact herbicide. This means it must come into contact with weeds to kill them. Acetic acid acts by dissolving cell walls, which allows fluids to leak out. This dries out the plant, potentially killing it. This method is more effective on younger plants and those with thinner skins. Tough, woody plants are more resilient, resulting in a burned appearance while remaining alive. Repeated treatments are often needed to kill off tenacious perennial weeds. Unsprayed parts are not affected. Plants accidentally sprayed are affected, as with any chemical overspray.
You cannot buy acetic acid at the grocery store, but you might find it at a garden center. If you decide to use acetic acid to clear out some tough weeds, do not use your aluminum sprayer. Acetic acid will damage aluminum and iron surfaces.
As with any pesticide, it should only be used on plants listed on the label, and it the manner described in the instructions. And be sure to wear eye protection and other personal protective equipment (PPE) when applying acetic acid.
Vinegar as herbicide
If you spray weeds with household vinegar, the aboveground portion of the plants might dry up and die. Or, it might not. It will not affect the root system. By the time the vinegar filters through the soil to reach the roots, it will have gone through chemical changes that make it practically harmless. And what do weeds do when you kill off the aboveground portion? They come back, again and again, ready to produce thousands of little weed seeds.
Of course, if you treat weeds repeatedly with vinegar, you will eventually force the plant to use up all the food stored in the root system, killing the plant. Probably. But honestly, it would have been simpler to just cut it off or pull it out in the first place.
Let’s stop sharing these myths about vinegar in the garden and leave it in the kitchen where it belongs.
That being said, if you have a bad sunburn. try gently wiping the affected area with a cloth soaked in vinegar. You might smell like a salad, but it won’t hurt anymore. I have no idea why.
Transpiration burn may sound like a used car deal gone bad, but it is a symptom of mite infestation that can significantly reduce your pear crop.
What is transpiration?
Transpiration refers to the way plants release water into the atmosphere through tiny openings, called stoma. Stoma are mostly found on the underside of leaves, but they also occur on stems and flowers. Stoma open and close to allow for the gas exchange necessary to photosynthesis [carbon dioxide in; oxygen out]. Transpiration also helps move plant nutrients, such as zinc, into and around within a plant.
The combined effects of plant transpiration and evaporation of water from the soil is called evapotranspiration. Maintaining the proper balance of water within a plant is critical to its health. When mites start feeding, that balance is threatened.
Types of mites
There are over 42,000 different types of mites in the world. They can be black, yellow, green, brown, or red. They are tiny. The most common mites in the San Francisco Bay Area include gall mites, spider mites, European red mites, and thread-footed mites. There are mites that prefer buds, mites that raise blisters (on plants), and mites that create a rust pattern. All mites have piercing mouthparts which are used to suck nutrient rich fluids from your plants. This can be a serious threat to plant health, especially in areas with scorching summers that are prone to drought.
Damage caused by mites
Mite feeding often causes stippling, tiny white or yellow spots, on leaves. Each of these spots represents a place where plant tissue has been pierced and the nearby fluids removed. Further feeding can lead to bronzing. As temperatures rise and mite feeding continues, transpiration burn can start killing leaves and reducing your crop.
Symptoms of transpiration burn
Transpiration burn occurs when mite feeding reaches critical levels. The accumulated water loss from mite feeding reaches a point where entire areas of the leaves die, leaving spots of dead brown or black tissue. This is referred top as transpiration burn and it is most commonly seen on pear leaves.
Transpiration burn halts photosynthesis and can lead to early leaf drop. Less leaf area means less photosynthesis, which results in smaller crops and unhealthy trees.
Preventing transpiration burn
A large, properly hydrated tree can lose up to 100 gallons of water a day during the peak of summer. Proper irrigation, using irrigation rings or soaker hoses, can prevent water stress to fruit and nut trees. This helps your trees counteract the damage caused by mites.
Mite control is tricky. These pests quickly develop resistance to chemicals, so pesticides don’t work. You can use a strong stream of water from a garden hose to displace mites. You can also buy predatory mites that hunt and feed on the mites feeding on your plants. Insecticidal soaps and oils can also be used, but care must be taken that these products don’s cause sunburn damage or other problems.
Keep your plants healthy and monitor them regularly for webbing and stippling, so you can deal with mite populations before they get out of hand.
You can grow a surprising amount of food in your own yard. Ask me how!