Young sunflowers track the sun across the sky, reaching new heights with every passing day - except, sometimes they don’t. Sometimes, a small injury can become infected and a black rot spreads around the base of the flower, finally engulfing it in a black goo that dries and hardens into a smelly shadow of what might have been. What causes this, and can it be prevented?
Head rot, also known as pin rot, is a disease of sunflowers, lettuce, and broccoli, caused by the Pectobacterium carotovorum, subsp. carotovorum and P. atrosepticum bacteria.
Symptoms of bacterial head rot
The first symptom of bacterial head rot is nothing more than a small, brown, greasy or water soaked looking area on the surface of a cluster of unopened flowers or leaves. These lesions are usually seen at the sight of mechanical injury caused by bird and insect feeding, hail, or falling twigs. Bacteria enter the damaged tissue and that’s where the infection begins.
Affected areas turn from brown to black as the infection spreads into surrounding plant tissue. There is a distinctly bad smell, similar to rotten potatoes, but it is rare for secondary fungal growths to occur when head rot is present. If the bad smell is absent and other bacterial and fungal infections are present, the infection is more likely to be caused by Alternaria fungi.
Bacterial head rot prevention and control
Cool winter and spring temperatures combined with prolonged periods of rain, fog, and dew provide the perfect medium for bacterial head rot pathogens. This means good air circulation between plants can go a long way toward preventing this disease. That’s a good thing, because chemical sprays and other treatments have not been consistently effective in preventing bacterial head rot.
The best way to prevent this problem in your garden is to start with resistant cultivars, such as broccoli with dome-shaped heads, space plants properly, and avoid overhead watering.
A cloche can protect young plants from cold, wind, heavy rain, and many small pests. Similar to the women’s hat of the same name, a cloche is generally bell-shaped, but it doesn’t have to be.
Early cloches were glass jars or boxes, placed over young plants to protect them from cold, frost, wind, and heavy rain. First used in France, cloches became popular throughout Europe in the mid-1600’s to provide restaurants and the wealthy with out-of-season produce. These jars were often ornate and delicate.
Cloches allow gardeners to get a head-start on the growing season. Greenhouses and cold frames work the same way. Modern cloches are mostly made out of plastic, and have largely been replaced with row covers. Small scale gardeners can still make use of more attractive, repurposed materials to protect young seedlings from the elements.
Cloches as pest protection
Solid-bodied cloches can provide protection for tender plants against caterpillars, snails, aphids, and many other pests. For a cloche to be effective against chickens, squirrels, and other larger pests, it has to be very sturdy and anchored in a way that can withstand repeated attacks.
While there are many sizes and shapes of cloche available for purchase, you can easily make your own. The most common DIY cloche suggestion is to use soda bottles or milk jugs by cutting off the bottom of the jug and using the lid to ventilate the cloche. The only problem with these ideas is that they add even more plastic to your garden soil.
How to use a cloche
Heat-loving plants, such as tomatoes, peppers, basil, and eggplant, get a much better start when protected with a cloche early in their development. Seeds or seedlings can be placed under a cloche after the soil has been watered. Most of the moisture will stay trapped in the cloche, but occasional waterings will still be needed as the plant grows. Because a glass cloche holds heat and air within, it can get too hot and too humid for your young plant. Occasional venting is necessary. To do this, simply slide a piece of wood or a rock under one edge of the cloche to increase air flow. In the evening, before temperatures start to drop, remove the prop and allow the cloche to sit flat on the ground again. If your cloche is made with fabric, venting is not needed. Once the plant outgrows the cloche, simply store it for another season or use it on another, smaller plant.
Cloches can also be used to help sensitive perennials make it through winter.
Whether you call them June beetles, Junebugs, or May beetles, these small, reddish-brown, clumsy flyers can be annoying. They get their name because of when they emerge. In the Bay Area, these pests come out in June. Other places get them in May, hence the difference.
Adult Junebugs feed on leaves. They fly in from weedy areas to feed at night. During the day, they tend to hunker down in a shady spot or burrow into the soil until dusk. The damage they cause is similar to Fuller rose beetles, earwigs, and snails. Grasshoppers and caterpillars may also cause similar damage. The only way to be sure is to catch them in the act.
The more insidious damage occurs underground as Junebug grubs feed on the roots of your lawn, especially ryegrass and bluegrass. Symptoms of infestation include brown, dying patches. If things get really bad, you can actually roll up patches of turf because it is no longer attached to the ground! Large numbers of Junebugs can defoliate a young tree in a matter of days. This is especially true for avocado trees, which may need to be protected with netting.
Commercial growers use blacklight traps when Junebug infestations cause too much damage. This is not recommended for home growers because the trap may attract more Junebugs than it captures. Heavy infestations are treated with an application of entomopathogenic nematodes. For the most part, home gardeners can’t do anything besides hand pick them whenever they are seen. Junebugs really are clumsy flyers, so it’s not hard to catch them. They are attracted to lights at night and often bump into windows and screens. When I catch them, I feed them to my chickens, who are very happy to help with Junebug control.
If you have children, you can always gift them a butterfly net and offer a bounty on every Junebug they catch!
Sometimes the best thing to do is to do nothing.
Allowing land (or a garden bed) to go fallow means giving it a period of rest. It sounds right, doesn’t it? Rather than digging, planting, irrigating, fertilizing, and harvesting, simply allow the soil a season to itself, to recover from the demands we place upon it every day. Like most things we discuss here at The Daily Garden, it really isn’t that simple.
The truth is, soil never rests
Fallow soil does what soil has always done. It provides structural support to root systems, it sequesters carbon, mineral nutrients, gases, and water. It also plays host to gazillions of chemical reactions and microscopic life forms. And the countless, amazing processes that take place in soil never actually stop and rest. [Unless, that is, it reaches sub-zero temperatures, and, even then, there’s probably still stuff going on!] Worms, insects, arthropods, mollusks, bacteria, fungi, algae, oomycetes, and chemical reactions continue, whether you plant tomatoes or not. Allowing soil to go fallow does, however, have certain benefits.
Benefits of fallow ground
Fallow ground enjoys uninterrupted natural processes that have evolved over billions of years. We know a lot, but we don’t know everything and everything. I like to believe that allowing soil to go fallow every once in a while gives time to life processes that we are not yet aware of, or that we do not fully understand. There are benefits to allowing land to go fallow that we do understand:
Different ways of doing nothing
There are different ways of allowing land to go fallow. First and easiest, you can completely leave it alone. Second, and my favorite, is to top dress the area with aged compost and then leave it alone. You can plant a cover crop that will be used as a green manure. This is called green fallow. You can till the soil (to control weeds) but plant nothing. This is called black fallow. [Doesn’t that sound like a movie title? Black Fallow Returns!] But I digress.
Cover crops on fallow land
Cover crops, such as fava beans, vetch, oats, barley, or rye can be grown on fallow land as a soil amendment, rather than a crop. These plants are left to their on devices and are treated as a green manure at the end of their normal life cycle. This returns all the nutrients to the soil, along with some excellent organic material that improves soil structure. This is especially beneficial if you have compacted soil or heavy clay. Cover crops have the added benefit of converting some nutrients into forms more usable by the next season’s crop. Having plants growing on fallow land also reduces erosion and provides food and shelter for beneficial insects. Although, ground-dwelling bees would really appreciate a small patch of bare ground, and chickens are always happy to do their part against the resident insect population!
A form of crop rotation
Allowing soil to go fallow should be part of your crop rotation or succession planting plan. Succession planting simply means sowing seeds in such a way as to constantly have something growing in a space, much the way plants grow naturally. Crop rotation allows you to keep a patch of ground as productive as possible, while switching up the crops being grown. This interrupts the lifecycle of certain soil pests, such as darkling beetles, nematodes, weevils, and wireworms. It also breaks the disease triangle for dieback, root rot, white rust, and other soil borne diseases. Incorporating a fallow year or season into the crop rotation cycle makes good sense for the health of your soil. This idea is not new
“Six years you shall sow your land and gather in its produce, but the seventh year you shall let it rest and lie fallow, that the poor of your people may eat; and what they leave, the beasts of the field may eat. In like manner you shall do with your vineyard and your olive grove.”
Allowing something to grow naturally on your fallow ground is an excellent way to hand over some of your garden tasks to natural processes for a season. If you watch closely, you may be surprised to learn something new about the way things grow in your garden!
Heliotropism refers to a plant’s ability to track the sun’s movement.
For many centuries, it was believed that a plant’s tendency to follow the sun as it crossed the sky was a passive action caused by water loss on the side of the plant exposed to sunlight. Now, we know that there is far more to it than that.
Growing toward sunlight
Instead of passively shrinking to one side as the sun’s harsh rays boil away a plant’s bodily fluids, we now know that plants actively grow toward (or away from) sunlight. [When a plant grows away from sunlight, it is called skototropism.]
Experiments conducted in the 1800’s demonstrated that plants will respond to any type of light: street lights, grow lights, or sunlight. When plants are attracted to this light, it is called phototropism. Phototropism is a function of the hypocotyl, or individual cells found in the same region. Hypocotyls are the embryonic stem found below the seed leaves (cotyledons) and directly above the root. You can easily see examples of phototropism when seedlings first emerge and they don’t get enough sunlight - they become leggy and lean toward whatever light they can. This is phototropism.
In heliotropism, not any old light source will do. It is only radiation from the sun that causes the reaction. And the mechanical causes of these two types of movements are very different.
Mechanics of plant movements
When plants move in response to the position of an external stimulus, it is called a tropic [TRO-pic] movement. If a plant’s movement is independent of the stimuli’s position, it is called a nastic movement. In phototropism, plant hormones (auxins), found in the meristem tissue of leaf and stem tips, photoreceptors, and multiple signaling pathways are used to direct a plant to grow more rapidly toward sunlight. In heliotropism, a structure called the pulvinus is used to direct movement.
The power of pulvinus
The pulvinus is an amazing, fluid-controlled joint found at the base of a plant leaf stem (petiole) or just below a flower.
The pulvinus causes movement by altering fluid pressure in the surrounding plant tissue. These changes in fluid pressure start when sucrose is moved from the phloem into the apoplast. The apoplast is the conjoined spaces between plant cells. As sugar is pumped into the apoplast, potassium ions are pushed out, followed by water molecules. This changes the pressure within the affected cells, causing movement. This is called turgor-mediated heliotropism. But not all heliotropic flowers have a pulvinus. Those that do not are still able to move by permanently expanding individual cells. This is called growth-mediated heliotropism. Pulvini are also used in response to nyctinastic and thigmonastic movements.
Heliotropic flowers face the sun from dawn to dusk. Slowly tracking the sun’s path across the sky, these flowers are believed to use heliotropism as a way to improve pollination, fertilization, and seed development. Heliotropic flowers often have five times as many beneficial insects present, due to the added warmth. [Many tropical flowers exhibit a modified form of heliotropism in which flowers maintain an indirect tracking of the the sun. This is believed to reduce the chance of potential overheating.] Beans, alfalfa, sunflowers, and many other species turn their blooms to follow the sun’s path across the sky each day. But sunflowers only use heliotropism in their early development, in the bud stage. Once a sunflower head emerges, it may track the sun for a short time, as an expression of phototropism, until the flower head reaches full size. The majority of sunflowers found in the northern hemisphere nearly always end up facing east.
Like floral heliotropism, leaf heliotropism is the method by which plants focus their leaves perpendicularly to the sun’s morning rays (diaheliotropism), or parallel to midday sun (paraheliotropism). Diaheliotropism allows leaves to capture the maximum amount of energy from the sun, while diaheliotropism protects plants from overheating and dehydrating.
How do your plants move during the day?
What bottle of wine would be complete without its cork? The same is true of most trees.
Everyone knows that trees and woody shrubs are made of wood, surrounded by bark. But there’s a lot more going on in those outer layers than meets the eye.
The bark you see protecting the living wood of a tree is made up of dead plant cells. This layer is called the rhytidome. The reason these cells are dead is because the cork layer cuts them off from the tree’s resources.
Components of bark
Bark is made up of three basic layers. The inner layer, or phloem, is a living part of a tree’s vascular system. Manufactured sugars ‘flow’ down the phloem to feed the rest of the plant. The middle tissue, or cortex, is made up of porous tissue that stores and transports carbohydrates, tannins, resins, and latex. The outermost layer of bark is called its periderm.
The periderm is also made up of three layers: the cork, cork cambium, and phelloderm. Cork (phellem) is produced by a specialized layer of cambium tissue, known as the cork cambium, or phellogen. This cork cambium layer is only one cell thick and the cells divide in parallel (or periclinally) toward the outside of the tree. In some trees, the cork cambium layer also produces cells towards the inside of the tree. These inner cells are the phelloderm layer.
Function of cork
Cork keeps wine safe from the elements because it is impermeable to gases and water. Because of the cork, your wine stays where it is and (as long as the cork remains intact) will only grow better with time. The cork of a tree also blocks air and water. Cork is able to keep trees and wine safe from the elements, along with insects, bacteria, and fungal disease because it contains suberin. Surberin is a waxy material that creates a protective barrier. This barrier also blocks water and gas exchanges between the outermost layers of the tree killing the epidermis, cortex, and secondary phloem. This is the bark you see.
Trees and shrubs also use cork to cut off an unwanted body part (leaf, diseased twigs, mature fruit) from the rest of the plant. This is called abscission.
Most fruits hang in their own singularity: apples, oranges, and apricots are common examples. Other fruits, such as grapes, form clusters. Still other fruits are formed when a group of flowers merge to create a fruit. Soroses are that type of fruit.
What is fruit?
Fruit is the fertilized ovary of a flowering plant (angiosperm). After pollination and fertilization occur, two new structures are produced: seeds (fertilized ovules) and pericarp (thickened ovary walls). In the case of apples and oranges, one flower produces one fruit. Sometimes, multiple flowers can fuse together to create a fruit. There are three different ways that this can happen:
In nearly every piece of literature you see, pineapples are listed as a common example of sorosis, but this is incorrect. I don’t know why they do this.
How a sorosis fruit develops
If you look at a mulberry flower cluster, you will see several flower buds held tightly together. Each of these individual flowers open up, awaiting pollination.
If you look closely, you can see tiny fruits at the base of each flower. Each of these fertilized fruits will develop around the stem that they emerged from in the first place. This is unlike pineapples, which include the receptacles and flower parts in their fruit development.
Berries vs. soroses
While mulberries may appear to have the same structure as blackberries and raspberries, botanically, they are quite different. Raspberries and other members of Rubus are made up of several drupes (a type of fruit) that are clustered around and attached to a dry thalamus. All of the drupes in a single fruit are made from a single flower. In mulberries, and other soroses, each rounded bit is its own fruit, formed from its own flower.
It won’t make any difference, as you enjoy a fig, some pineapple, or a mulberry, but now you can impress your friends with this fascinating word!
Some garden words are fun to say. Schizocarp [ˈskitsōˌkärp] certainly qualifies.
A schizocarp is a type of dry fruit that splits into single-seeded parts, called mericarps, when ripe. Each mericarp is made from its own carpel. [A carpel is the female reproductive parts of a flower, including an ovary, stigma, and usually a style.] Mericarps can be dehiscent, which means they split open when ripe, or indehiscent, which means they stay closed.
The seeds of carrots, celery, coriander, anise, dill, parsnip, and other umbellifers are all indehiscent schizocarps. Hibiscus (Malvaceae), mallows and cheeseweeds (Malva), false mallows (Malvastrum), and wireweed (Sida acuta) fall in the same category.
Members of the Geranium genus produce dehiscent schizocarps. [These are not the garden variety geraniums, which are another genus altogether (Pelargonium). I know, I know, it gets confusing.] True Geranium species include the cranesbill, horns’ bill and filaree plants that produce needle-shaped schizocarps that twist and gyrate into the soil (and were fun to play with, when we were children).
Maple trees produce winged schizocarps, called samaras.
Unlike the juicy fruits we enjoy each summer, or the dried caryopsis of cereal grains, plants that produce schizocarps have found that procreation works best when each flower produces a number of independent seeds protected by a dried fruit coating.
Now you know.
Clay soil is common in the Bay Area, and it can feel like concrete on a hot day. In fact, clay particles have electrical charges that hold them tightly to their neighbors.
The science of clay
Clay is just one type of soil. Soil is made up of varying combinations of sand, silt, clay, air, water, minerals, microbes, earthworms, and more. All those ingredients are arranged into soil structures called aggregates, which contain solids and spaces. [This is different from soil texture, which refers to the percentage of sand, silt, and clay found in a sample.] The particles of various minerals found in soil are measured in micrometers (μm), or microns [one micron equals one one-millionth of a meter]:
[For my Burner readers, playa dust can be 0.3 μm, or three-tenths of one one-millionth of a meter.
That's why you will never get it out of your car or your tent.]
The spaces between soil particles are called macropores and micropores. Macropores are greater than 0.08 mm and they hold air and water. Because the spaces are larger, water moves passively, pulled by gravity. Micropores are less than 0.08 mm and mostly hold air. Macropores are so small that the surface tension of water molecules means active suction must be used to pull the water out of these tiny spaces. Clay soil has far more micropores than macropores, so water and nutrients are held tightly, which means it is less porous.
Porosity, or permeability, refers to the ability of air and water to move through soil. Soil that is rich in organic material tends to have better porosity. Porous soil allows roots to find water and nutrients, and allows for healthy gas exchanges. Being flat, clay particles lie on top of each other like a deck of cards. This is why clay soil is so susceptible to compaction.
Clay and soil compaction
Compacted soil can create a barrier to roots seeking water, nutrients, and stability. It can even alter nitrogen, making it unavailable to plants (denitrification). This is especially true next to streets, driveways, buildings, and other heat islands. [If your unimproved clay soil ever feels spongey, it may indicate a masked chafer infestation.] On the other hand, leaching of nutrients is far less common in clay soil. More often, we end up with a super abundance of certain nutrients that creates an imbalance for our plants.
Clay soil and plant nutrients
Clay is made up of many negatively charged secondary minerals. That negative charge loves to attract and hold on to cations, or positively charged particles, such as potassium, zinc, and nitrogen. [That’s why most Bay Area soils have an abundance of potassium.] This attract-ability gives clay soil a high cation exchange capacity (CEC), which is a fancy ways of saying clay can hold onto 6 to 8 times more water and nutrients than sand. If you get a soil test (and I urge you to do so), you will also see a base saturation figure. To illustrate, CEC can be seen as the number of electrical outlets in your home, while base saturation is the number of those outlets currently being used. On average, sand has a CEC of 5-15, silt has a CEC of 8-30, and clay has a CEC of 25-50.
In the same volume of soil, clay has 100,000 times more surface area than sand, so there are plenty of places for attachments to occur. You can improve your clay soil’s base saturation by monitoring and correcting soil pH. Alkaline soils may need acidification, while acidic soils may need the addition of lime to bring the pH into a range suitable for plant growth (6.0 to 7.0). A proper pH can make important nutrients, such as iron, available to your plants.
Safety note: When planting trees around your home, keep in mind that root systems of plants growing in clay tend to be smaller, because so many more nutrients are available closer to the tree. This can result in a smaller in-ground support system for your tree, which makes it more likely to fall. Just sayin’…
Clay and drainage
When soil is extremely dry, it can’t absorb water because it becomes hydrophobic. Like a dry sponge, the water simply rolls off. Clay soil can act the same way. The rate at which water can enter soil is called its infiltration rate. Infiltration rates are given as millimeters of water absorbed per hour:
Because clay drains so slowly and can hold so much water, poor drainage can lead to fungal disease. This is particularly true for beans, stone fruits, and cucurbits. Proper irrigation of plants grown in clay soil means watering slowly and gently. Overwatering clay soil can drown your plants. Also, to avoid smooth dinnerware-like edges and compaction, avoid walking on or working wet clay soil or mud.
In areas prone to heavy rains, rain gardens can be used to offset the risk of flooding and fungal disease. Rain gardens divert excess water into sunken areas, away from buildings and vulnerable plants, filtering that water and allowing it to be absorbed slowly, without causing runoff or pollution.
Transplants and bare root trees
Because clay particles fit together so tightly, your soil can become as hard as a piece of pottery, making it difficult or impossible for transplants and bare root trees to get established. When installing stone fruit crops, such as nectarines, almonds, and apricots, you will need to be sure to rough up the edges of the planting hole to make it possible for new roots to work their way into the surrounding soil. In fact, roughing up these edges is a good idea for all your transplants.
Plants that must have good drainage to avoid fungal problems, such as crown rot, are often planted in mounds. This added elevation keeps moisture away from the crown. This practice is common when installing avocados, olives, squash, and melons.
Improving clay soil
Mulching and composting are the best ways to improve the structure of heavy clay soil. As the organic materials break down, they increase the number of spaces between the clay particles. This allows air, water, and roots to move through the soil more easily. It also improves drainage and permeability. Other ways to improve soil structure include aeration, sprinkling coffee grounds on the soil, incorporating perlite, and cutting plants off at ground level, rather than removing them, roots and all. Those roots play host to millions of soil microbes that help maintain healthy soil. As you work to improve your clay’s structure, you can still garden using raised beds, vertical gardens, keyhole gardens, and containers. Whatever you do, do not add sand.
The Sand-Clay Myth
Our intuition tells us that we can lighten heavy clay soil by adding sand. It sounds right. Sand has plenty of spaces, right? Putting the two together should give us a nice, happy medium, right? Wrong. Instead, the tiny clay particles fill in all the spaces around the sand grains, creating a soil that is even heavier than before!
Clay and plant choice
While dandelions' taproots seems able to penetrate concrete, many plants have a difficult time getting established (ecesis) in compacted clay soil. Some plant families, such as the sunflower family, need a regular top dressing of aged compost to perform well in clay soil. These plants include artichoke, lettuce, and tarragon. Other plant families, such as the parsley family, simply cannot thrive in clay and are better grown in containers. This group includes carrots, celery, parsnips, and fennel. The allium family of onions, garlic, and chives can be grown in clay soil, but the addition of organic material will help them thrive. The same is true for lilacs, and members of the mint family, such as lavender and salvia. Beets and Swiss chard prefer loose soil, but can be grown in amended clay soil.
Berries are shallow-rooted plants that really prefer loose soil. If you have clay soil and want to grow blackberries, raspberries, blueberries, or strawberries, you will want to work a lot of aged compost into the soil before planting.
Some plants are so rugged that they can help break up compacted clay soil. These plants include cilantro, cowpeas, and fava beans. Other plants, such as germander, yarrow, and sage, seem to barely notice hard-packed clay soil, as long as they get a little water during the peak of summer, which makes them excellent ground covers. Olive and plum trees, like many herbs, seem to thrive in less than ideal soil.
The “other” clay
The finely textured clay used to make porcelain, called kaolin clay, can be used to protect many crops from damage by insect pests such as codling moth, stinkbugs, cucumber beetles, squash bugs, cabbage loopers, aphids, cutworms, and armyworms, just to name a few. Apparently, insects don’t like getting kaolin clay on their feet, so they go elsewhere. Your watermelons, apples, and peaches will thank you!
Did you know that clay, sand, animal dung, and straw are used to plaster woven stick fences? It’s called pleaching!
It is normal and healthy for the pruned tip of a twig to dry up and seal itself off from pests and disease. When the tip of a twig dies and that death keeps moving inward, there’s a problem. This creeping death is called dieback. Dieback can be caused by environmental conditions, insect feeding, or disease.
It is not understood why, but delayed leafing out seems to be associated with dieback. This may simply be because dieback may be caused by the same environmental conditions that cause delayed leafing out. We really don’t know. These conditions include winter drought, extreme cold, or insufficient chilling hours. This form of dieback is common in blackberries and raspberries. Other causes of dieback include poor irrigation and hot, dry winds, potassium or zinc deficiencies, phosphorus toxicity, and insect feeding by shot hole borers, black scale, wooly aphids, and mealybugs. Also, when the raspberry horntail, a tiny wasp, lays its eggs in a raspberry or blackberry cane, dieback can occur.
Dieback by nematodes
Nematodes are microscopic, eel-like roundworms that live in the soil. Some nematodes are beneficial predators, and some are plant-eating, disease-carrying parasites. Nematode feeding can cause reduced plant vigor, wilting, smaller fruits and leaves, and twig dieback.
Several different fungi can cause dieback. Each pathogen has its own set of symptoms and host plants:
Lettuce is susceptible to a viral dieback caused by the lettuce necrotic stunt virus. Formally called ‘tomato bushy stunt virus’, this pathogen causes stunting, leathery, dark inner leaves, and rotted areas on outer leaves.
Apple, citrus, stone fruits, and pear are susceptible to bacterial blast, blight, and cankers, all of which are caused by Pseudomonas syringae. This pathogen kills flower clusters and nearby leaves, along with twig tips. Fireblight is another bacterial infection that causes twig dieback. This disease is easy to spot because the dead twigs curl themselves into a shepherd’s crook shape. Watch for fireblight in June. Huanglongbing, a deadly disease of citrus, includes twig dieback as one of its early symptoms.
How to prevent dieback
Plants that are healthy can often protect themselves from dieback. These tips can help reduce the risk of dieback in your garden and landscape:
Clearly, there are many causes of dieback. Taking the time to determine the reason for twigs and stems dying back can help you find an effective treatment.
Lack of vigor or sudden death by the phytophthora root and crown rot is nearly always caused by too much water.
The name is from the Greek phytón (plant) and phthorá (destruction), so the name Phytophthora means the plant-destroyer. There are different types of Phytophthora that attack different host plants.
What is Phytophthora root and crown rot?
Phytophthora [fie-TOF-ther-uh ] is a family of water molds, called oomycetes. Oomycetes fall somewhere between fungi and algae in the web of life. There are many different types of Phytophthora molds. They generally attack stems and roots. Stem damage normally occurs at or just above the crown, where the stem meets the roots, at the soil line, though it can also occur elsewhere on a plant. These molds cause many different plant diseases, including sudden oak death, potato blight, damping-off disease, and crown rot. Phytophthora root and crown rot, in particular, can kill a tree or shrub if the soil remains wet for too long, or when planted too deeply. [Moist soil around the trunk is never a good idea.]
Nearly all fruit and nut trees, including cherries and kiwifruit, are susceptible to Phytophthora root and crown rot. But so are alfalfa, and members of the nightshade and cabbage families. This means tomatoes, eggplant, and potatoes are vulnerable, as are kale, cauliflower, Brussels sprouts, broccoli, kohlrabi, horseradish, cabbage, collards, turnips, rutabagas, radishes, bok choy, and mustard. And all because of too much water.
Symptoms of Phytophthora root and crown rot
Plants affected by Phytophthora root and crown rot look drought stressed. This is particularly unfortunate because the natural response is to provide more water - the last thing you want to do when Phytophthora is present. Symptoms normally start in just one branch or area of the tree or shrub before spreading to the rest of the plant. Leaves may turn purple or reddish. Sudden wilting and plant death may occur when the basal stem or crown are attacked, or the mold may attack the root system, causing plants to linger poorly for years before dying.
Symptoms can vary greatly, depending on the type and age of plant, the plant’s genetic resistance to infection and overall health, as well as soil temperatures and moisture levels, but you will probably see darkened areas of the bark around the crown and upper roots of infected plants. You may also see dark sap or gum oozing from damaged areas. Using a sharp knife, you can cut away an area of bark. Infected trees will show reddish brown streaks or patches. Water-soaked areas on roots may also be visible. If you also see white threads between the bark and the inner layer, or around the roots, the infection is from Armillaria root rot, rather than Phytophthora.
Preventing Phytophthora root and crown rot infestation
Proper water management is the best way to prevent and control Phytophthora root and crown rot. Never allow standing water to remain around tree and shrub trunks. Also, don’t let sprinklers hit tree trunks. These other tips can help you manage Phytophthora in your garden or landscape:
You may be able to maintain an infected plant, with proper irrigation and good cultural practices, but it will never be the same. Phytophthora can stay in the soil for many years, so prevention is far easier than control.
NOTE: One new-to-us variety, Phytophthora tentaculata, is on the Dept. of Agriculture’s watch list. If it appears in your garden or landscape, please contact your local Cooperative Extension Office right away. They may have helpful advice that will protect your plants, and they need to know how far this disease is spreading.
Ginger’s sweet bite makes it an excellent addition to many favorite foods, and it can be candied for a special treat. And you can grow it at home!
The ginger plant
Ginger was one of the first spices to be exported from the Orient and it is a fascinating plant. As a plant family in its own right, ginger (Zingiber officinale) is cousin to turmeric and cardamom.
The ginger we eat is not actually a root. It is a rhizome. Rhizomes are modified, underground stems that put out lateral shoots and adventitious roots. Ginger plants do not have aboveground stems. Instead, they grow much like the grass in your lawn, with leaves rolled together at the base of the plant to form pseudostems, except that they can grow to three or four feet tall! Equally tall floral stems emerge directly from the rhizome. Flower buds start out green and then turn white and pink before opening up into mature flowers. Mature flowers can be pale yellow, deep purple, or brilliant red, depending on the variety.
How to grow ginger
Ginger needs loose, nutrient-rich soil, so it is best grown in containers. This makes it easy to bring indoors as temperatures drop in winter, as well. Most grocery store ginger ‘roots’ are treated with chemicals that prevent them from sprouting, but not always. While I normally warn against planting grocery store foods, due to the potential risk of introducing a safe-to-us-but-bad-for-plants disease, your ginger will, most likely, be growing in a container, so it’s not really an issue. Rinse off the ginger and place it in a container filled with potting soil, just under the soil line. Keep the soil moist but not soggy to encourage growth. Being from the tropical rainforest, your ginger plant will need lots of warmth, moisture, and protection from intense sunlight. [Under the canopy, jungles are actually pretty dark!]
While you can harvest ginger rhizomes at any time, it is best for the plant’s long term health if you wait until the aboveground portion withers, similarly to garlic. The desired portion of the rhizome is cut off and the rest of the plant can be returned to its container. The cut off portion is then scalded to prevent it from sprouting. The older ginger gets, the tougher and drier the rhizome becomes. Ginger is a perennial plant, which means it keeps on growing. It may look as though it dies in winter, but don’t be fooled. Unless your region is too cold for ginger, it will come back year after year. Each little nub on a ginger rhizome is a potential new plant.
Why buy ginger shipped from around the world when you can grow your own?
Seeing unripe fruit or nuts on the ground, under your tree, can be normal, or it can indicate a problem.
Fruit drop, or June drop, is a natural process which allows a tree to get rid of more fruit than it can support. This is common behavior for citrus, apples, avocados, and many other crops. Some trees, such as loquat, can be messy during this time. Manual fruit thinning works in the same way, reducing quantity, but improving quality. Fruit drop can also indicate insect pests, disease, or adverse environmental conditions. Earlier in the growing season, some trees will rid themselves of unwanted blooms in an action called blossom drop, for the same reasons.
Fruit drop caused by insects
Black scale feeding weakens the tree, leading to wilting, twig dieback, stunting, and early fruit drop. Scale insects’ cousin, the mealybug, can also cause early fruit drop, along with chlorosis and sooty mold. Feeding by mites can also reduce a tree’s ability to support a crop, causing fruit drop. Finally, while weevils are better known for burrowing into beans, cotton bolls, and cereal grains, they also feed on roots, stems, buds, flowers, leaves, and fruit. Often, the first sign of a weevil infestation is leaf wilting, scalloped leaf edges, and early fruit drop.
Fruit drop caused by disease
Trees will frequently abort diseased or malformed fruit, rather than investing water and nutrient resources in fruit that won’t reach maturity.
Fruit drop caused by environmental conditions
Sudden cold or extreme heat can cause fruit drop, especially in young trees. Strong winds can also blow unripe fruit from your trees. The most common environmental cause of excessive fruit drop is insufficient irrigation or unbalanced soil nutrients. This is especially true for almonds and tomatoes.
Pollination and fruit drop
Fruit drop can also be caused by insufficient pollination. This may be because a particular variety of fruit or nut tree needs a genetically compatible tree that it can use for cross-pollination. It can also mean there are not enough pollinators in your area. You can attract more pollinators to your garden by avoiding the use of broad spectrum pesticides and by installing a wide variety of flowering plants. Or, you can start raising honey bees, as I have! [Honey bees take up surprisingly little space and they boost pollination of nearly all your crops - plus, you get honey!]
Fruit drop and pruning
If you need to perform heavy pruning as fruit is developing, the tree may not have the food-producing capability that it had before the pruning job, so fruit drop will occur. Unless it is absolutely necessary, it is far better to leave pruning and tree training for the dormant season.
Fruit drop and the soil
Low magnesium (Mg) levels in the soil can cause fruit drop, as can high potassium (K) or boron (B) levels. You can’t know what your soil’s nutrient levels are without a soil test from a local, reputable lab. While they look convenient and appealing, over-the-counter soil tests are not yet good enough to be useful. I’m still waiting for some aspiring entrepreneur to make that one happen - there’s a huge market for it, but I digress. The type of soil can also have an impact on fruit drop. Sandy soils are far more prone to fruit drop than heavy clay soil.
So, don’t panic if your orange tree drops dozens or hundreds of tiny green fruits in May or June. This is normal. Just pick them up and add them to your compost pile. If you notice heavy insect infestations, signs of disease, chlorosis, or wilting, you will want to track down the cause and correct it for a healthy harvest later in the season.
And always remove fallen fruit and mummies, to avoid creating a disease triangle, or a hotel for pests.
Plants cannot be green without magnesium, but too much magnesium in the soil can turn plants yellow. How can this be?
Magnesium is essential for plant health. Magnesium stabilizes cell membranes, making plants better able to withstand drought and sunburn. Magnesium is found in enzymes that plants use to metabolize carbohydrates. Most important, magnesium is contained in the chlorophyll molecules that convert the sun’s energy into food. This process, the Calvin Cycle, is what makes photosynthesis possible. Clearly, magnesium is important to plant health. But too much magnesium can interfere with the absorption of other plant nutrients.
Plants use 13 dissolved minerals as food. There are three primary macronutrients (nitrogen, potassium, and phosphorus) and three secondary macronutrients (calcium, sulfur, and magnesium). Plants use large amounts of these macronutrients to grow, thrive, and produce. Seven other nutrients, used in smaller amounts, are called micronutrients. Fertilizers claim to provide all the food your plants need, but it’s not that simple. [Is it ever?]
The chemical interplay, taking place in the soil, that allows plants to absorb nutrients, is a delicate balancing act. Too much, or not enough, of one nutrient can create a domino effect that causes starvation for plants that are surrounded by a banquet of nutrients.
What is magnesium?
Magnesium is an elemental metal. Pure magnesium (Mg) is too stable of a molecule for plants to absorb. The less stable, cation form of magnesium (Mg2+) is a dissolved salt that plants use for food. To be able to attract and hold those positively charged molecules, plants also need negatively charged molecules (anions), such as nitrogen, phosphorus, and sulfur. The ability of soil to perform this balancing act is called its Cation Exchange Capacity (CEC). Without a soil test from a reputable, local lab, you cannot know your soil’s CEC or nutrient levels.
For example: My first soil test found magnesium levels of 798 parts per million (ppm). The ideal range is 50 to 120ppm. Clearly, before I moved in, someone was applying an awful lot of fertilizer. The problem they were probably trying to correct was not insufficient nutrients, but a nutrient imbalance. Without a soil test from a local, reputable lab, you simply do not have enough information.
Base saturation and magnesium
Soil test results also include base saturation figures for potassium, calcium, and magnesium. Base saturation is the percentage of available connections being used. [Think of it as how many grocery bags you can carry in from your car.] The optimal range for magnesium base saturation is 10 to 30%. This means that soil particles, because of their electrical charge, will ideally hold on to 10 to 30% of the magnesium in the soil. It takes the right absorption percentage and the right volume of magnesium in the soil for plants to be healthy.
My soil’s magnesium base saturation was 32%. That sounds close enough to the 10 to 30% optimal range, right? The problem is, with seven times the amount of magnesium needed in the soil, my plants were getting 32% of too much.
Too much magnesium in the soil makes it difficult for plants to absorb calcium and other anion nutrients, which can lead to blossom end rot, bronzing, and many other problems. This is a common problem in areas with alkaline soil. The opposite is true in areas with acidic soil. Insufficient magnesium symptoms look very much like potassium toxicity symptoms: older leaves, at the bottom of the plant, start turning brown, between and alongside the leaf veins, working upward through the plant. Magnesium deficiencies in stone fruits often start out as slightly brown areas along leaf edges (margins) that expand inward, causing cracking, necrosis, and leaf loss. Magnesium deficiency in California is extremely rare.
Stabilizing magnesium levels
Reaching and maintaining ideal mineral levels in soil for healthy plant growth is both science and art - mostly science. To start, get a soil test from a local, reputable lab. Unfortunately, over-the-counter soil tests are not yet accurate enough to be useful. Once you have your results, you can take these other factors into consideration:
Finally, schedule regular soil tests for your garden and landscape. Look at these tests as an annual physical for the living skin of your property. The information in these tests will help you make informed decisions about the magnesium in your soil.
If older leaves on cucumber, melon, or squash are turning yellow and leathery, the plants may be infected with cucurbit aphid-borne yellows.
This viral disease is transmitted by the cucurbit aphid-borne yellows luteovirus (CABYV). Luteoviruses are a genus of viruses that use plants as hosts, and are transmitted by aphids.
Symptoms of aphid borne yellow virus
Early symptoms are chlorotic (yellow) areas on lower leaves. These spots expand to include the entire leaf, leaving the larger veins bright green. The affected areas become leathery and brittle. Stunting and fruit drop are common as the plant struggles. Before genetic testing, this condition was attributed to plant aging (senescence), nutrient deficiencies, or other diseases, such as cucurbit yellow stunting disorder.
How the disease is spread
As the name suggests, this disease is spread by aphids. As aphids pierce plant tissue to feed on sap in the xylem, they infect the plants they eat. Once infected, the aphid will continue to spread the disease as it feeds. This disease can also be spread to lettuces, beets, and several weeds.
Controlling cucurbit aphid borne yellows
There is no way to control the virus, but you can reduce the presence of aphids in your garden with these tips:
Infected plants should be removed and destroyed, to prevent the disease from spreading to nearby plants.
Fresh, sweet cherries are delicious, but cherry trees can be difficult to grow.
According to UC California Backyard Orchard, “cherries are the most difficult trees to keep alive.” If you are still determined, let’s see what we can learn about these trees.
People have been enjoying cherries since prehistoric times. Cherries are stone fruits, which means the fruit is a drupe. There are two types of cherry trees: sweet (Prunus avium) and sour (Prunus cerasus). The two cannot cross-pollinate with each other. Both types are native to Europe and western Asia. Sweet cherries are also known as wild cherries or gean.
How to grow cherry trees
Cherry trees cannot tolerate soggy ground and they need a lot of sunlight. Excellent drainage is critical. So much so, that cherry trees are generally planted on mounds, or berms. Trees should be spaced 14 to 20 feet apart, and you are going to need at least two because most sweet cherry varieties require cross-pollination to bear fruit. Sour cherries, the type used in pies and preserves, are self-fertile and do not require cross-pollination.
While installing bare root stock is preferable, you can grow a cherry tree from a pit. The pit will need to be exposed to cold temperatures (stratification) before it will germinate. When selecting a cherry variety for your landscape, be sure to choose one with a chilling requirement that matches your microclimate. The tree will set fruit in 3 or 4 years.
Seasonal care for cherry trees
Each winter, you will need to prune out 10% of the previous year’s growth, as well as any dead, damaged, diseased, or crossing/rubbing branches. You will also want to apply dormant oil. An application of fixed copper can help reduce bacterial canker (gummosis). In spring, as blossoms appear, apply a fungicide, such as Bordeaux mixture, to control brown rot, and feed each tree 2 lb. of urea or 70 lb. of aged manure just before a deep watering.
Birds will enjoy your cherries long before you do if you do not protect your crop with netting or a tree cage. Trees will need to be drip irrigated every day in summer, or given 3 to 5” of water every 2 or 3 weeks. After harvesting your cherry crop, feed each tree with 2 lb. of urea and irrigate right away. Keep trees irrigated regularly until September, then stop watering altogether. This will help prevent root rot.
Cherry pests and diseases
It is astounding to learn how many diseases and insect pests can interfere with growing cherries. If birds, squirrels, and pocket gophers weren’t bad enough, cherry trees are are regularly attacked by a wide variety of insect pests:
Black cherry aphids, cherry slugs, earwigs, green fruitworms, western flower thrips, nematodes, and cribrate weevil can also be added to that collection. And the list of cherry diseases is no less daunting:
Cherries are also susceptible to a genetic disease, called leaf crinkle, and a couple of mysterious diseases, called cherry necrotic rusty mottle and cherry stem pitting, that occur when grafting scions. Applying sticky barriers to the trunks of trees can block crawling insects, but it does nothing against flying insects.
Bottom line: cherries are probably best left to the professionals. Hopefully, this information will help you appreciate just how much effort goes into providing these delicious summer treats. If you decide to give cherries a try, please share your experience with us in the comments!
Neonicotinoids are a class of insecticides.
When neonicotinoids first came on the market in the 1980’s, they were touted as a cure-all for garden pests around the world. Since neonics affect certain receptors in an insect’s nervous system, humans and other mammals, birds, and fish would be perfectly safe, they said. That sort of marketing should have been a warning from the beginning. What quickly followed were massive bee die offs, and threats by the EU to regulate this class of chemicals, but it's not that simple. To understand the pros and cons of this insecticide, we need to know more about how it works.
What are neonicotinoids?
Neonicotinoids, or neonics, as they are more conveniently known, are a class of insecticides that are chemically similar to nicotine. This class of chemicals includes several ingredients you may see on a bottle of insecticide:
After the disaster of DDT, other chemical insecticides were tried. Organophosphates and carbamates were the most common, but these are far more toxic than the neonics. By 2013, according to YaleEnvironment360, 95% of the U.S. corn and canola crops, most of the cotton, sugar beet, and sorghum crops, and a “vast majority of fruit and vegetables, including apples, cherries, peaches, oranges, berries, leafy greens, tomatoes, and potatoes, to cereal grains, rice, nuts, and wine grapes” were sprayed with neonics.
How do neonics work?
Neonicotinoids work by interrupting an insect’s nervous system. Since insect nervous systems are so different from other living things, these chemicals are generally safe, as far as poisons go. Initially, plants and seeds were sprayed with neonicotinoids. Neonics are systemic, which means they can be sprayed on seeds or plants, or watered in. Sprayed seeds grow into plants that contain the insecticide. Sprayed plants absorb the chemical, which is then spread throughout the plant via the xylem. When an insect comes along and takes a bite, or grabs some nectar or pollen - WHAM! They’ve been poisoned.
Problems associated with neonics
The initial problems with neonics occurred when seeds were sprayed with the chemical and then put through a seed spreader that created clouds of neonicotinoids, killing tens of thousands of honey bees. Also, sprayed insecticides tend to go all over the place, causing overspray damage to nearby plants, waterways, and air. Of course, all this made the news and got everyone excited, but those particular problems have been resolved in most countries.
Now, neonics are more commonly applied as a drench, which is poured into the soil, to be absorbed by the roots. This eliminates overspray. Treated seeds are now managed in ways that prevent the pneumatic seed dispersal issue. Currently acceptable application rates seem to only be causing minimal harm to honey bee colonies, but they are still devastating to native bee populations.
Does your garden really need chemicals?
Individuals impact the amount of chemicals found in the environment by thinking before buying:
As we have learned in the past, spraying chemicals all over the place ends up causing unexpected problems. These chemicals start building up in our ground water and soil. Also, insects evolve much faster than we do. It is common for insects to develop a resistance to the poisons we spray on them, while we remain vulnerable.
Neonicotinoids may or may not be the next DDT. The truth is, we don’t know. What we do know is that there are better ways for home gardeners to care for their plants than to inundate the environment with chemicals.
If you pick a dandelion, you will see a viscous, milky white goo come out of the stem. That goo is latex. Exposed to the air, latex coagulates, creating a protective barrier. Plants use latex as a defense against insect feeding. [Slugs will eat leaves drained of latex, but not before.] We use latex in very different ways.
Latex gloves, latex paint, and cosmetic sponges all get their start from latex. So do chewing gum, balloons, adhesives, and opium. The latex collected from the rubber tree is where we get, you guessed it, rubber. [Most latex paint, such as is used in whitewashing, is actually a synthetic latex.] It is estimated that 10% of all flowering plants, angiosperms, contain latex.
What is latex?
Latex is an emulsion made up of of proteins, fats, starches, sugars, oils, resins, alkaloids, tannins, and gums. Emulsions are mixtures of two or more liquids that generally do not mix - think salad dressing. Homogenized milk and mayonnaise are also emulsions. Normally, latex is thick and white, but it can also be yellow, clear, orange, red, or watery.
How is latex different from sap, or resin?
Sap is the combined water, sugars, and plant nutrients that move through a plant’s vascular bundles to feed and water the plant. Resins, like latex, are protective substances that ooze from injury sites. Unlike latex, which coagulates and dries, resins create a hard, crystalline barrier.
How do plants make latex?
Latex is produced and transported in a separate system called the laticiferous system. There are two methods of latex formation and movement. Articulated laticifers consist of rows of plant cells found in the meristem tissue of stems and roots. The walls of these cells dissolve, creating tubes, called latex vessels. This method is common to poppies, fig trees, mulberries, rubber trees, and members of the sunflower family. Non-articulated laticifers, such as milkweed and spurge, develop a branching network of latex-producing cells throughout the plant. In some cases, the entire network is made from a single cell.
Plants that produce latex
There are over 20,000 species of plant that produce latex, occurring in over 40 plant families. Some of the more commonly known latex-producing families include:
Some mushroom, conifer, and fern species also produce latex as a defense mechanism.
Allergic reactions to latex
Because latex contains defensive chemicals, it can be an irritant. Prolonged exposure can lead to an allergic response, as can multiple surgeries, or spina bifida. Individuals with a latex allergy are at risk for anaphylactic shock and should avoid contact. Some forms of latex can cause blistering of the skin, or blindness, while other plants produce a latex with reduced amounts of the allergen. These forms are being researched as an alternative.
As you work in the garden, note which plants exude latex when damaged. And monitor your skin for reactions to this liquid plant defense.
Crawlers with no legs, a species with no males, and broody females who keep thousands of eggs warm and safe - what are these garden pests? Citricola scale.
Native to Japan and southern China, citricola scale is currently found in California, Arizona, and Maryland, and in several other countries. Also known as grey citrus scale, citricola scale (Coccus pseudomagnoliarum) can be found feeding on citrus and pomegranate twigs in spring and early summer, and immature scale insects can be found feeding on the underside of leaves in late summer and fall. In addition to feeding on pomegranate, lemon, lime, orange, and grapefruit, these sap-sucking pests also feed on elm, bay laurel, hackberry, and oleander.
Citricola scale lifecycle
There are only female citricola scale insects. They reproduce asexually (parthenogenesis). Each female can produce between 1,000 and 5,000 eggs during the summer. She will keep her eggs safe under her body until they hatch out in to crawlers, usually from June through August. That may sound like a crazy broody season, but citricola scale eggs hatch after only 2 or 3 days. The babies that come out of those eggs are called crawlers. The name crawlers sounds a little misleading because they don’t look as though they could do anything. But they do. These crawlers move to a good feeding site, attach themselves, becoming sessile (fixed), and feed until they molt into second instar nymphs, usually around November. These nymphs produce a lot of honeydew and are often protected and farmed by ants.
Citricola scale description
Citricola scale start out as a yellow, oval egg. First instar crawlers are oval, flat, and nearly translucent. Sometimes they are yellowish-green to brown. Second instars are mottled brown. Citricola scale adults are one-quarter of an inch long, grey, oval, and flat. Well, slightly convex, but flat enough. They can be difficult to see because they start taking on the color of the twig to which they are attached. Citricola scale are often confused with brown soft scale.
Citricola scale or brown soft scale?
Citricola scale tends to have only one or two generations each year, while brown soft scale can have multiple generations going at any one time. This means that citricola scale insects you see will nearly always be at the same life stage, while brown soft scale specimens may be at any life stage. Also, adult citricola insects are grey, while brown soft scale adults are brown or yellow.
Damage caused by citricola scale
Underneath those tiny domes of protection, citricola scale attach themselves to stems and leaves of citrus and pomegranate. They pierce the surface to reach the phloem, to siphon away valuable nutrients and sugary sap, weakening the tree. And they poop. This poop, called honeydew, contains a lot of sugar, and it creates the perfect growing medium for sooty mold fungus. Sooty mold blocks photosynthesis, further reducing your tree’s vigor. Citricola scale can reduce flowering and fruit production. During heavy infestations, twigs can be killed by citricola scale.
How to control citricola scale
Regularly monitoring citrus and pomegranate trees for these pests is your first line of defense. If you notice ant trails or sooty mold, take a closer look at twigs and leaves for signs of scale. Since ants protect these pests, you can eliminate that protection, making the citricola scale more vulnerable, by wrapping the tree’s trunk with a sticky barrier. Also, there are naturally occurring parasitic wasps that will control citricola scale insects (as long as you do not apply broad spectrum pesticides). Applying dormant oil in winter can also help reduce citricola scale populations.
Research has shown that 40% of citricola scale in San Joaquin Valley are resistant to organophosphates. It is believed that there is also a cross-resistance to malathion and carbaryl. This looks to be yet another example of chemical pesticides actually making the pests stronger, as we add more poisons to the environment and our food chain.
Bottom line, to control citricola scale on your pomegranate and citrus trees, inspect twigs very closely in April through June, and then look at the underside of leaves in late July. These pests can then be flicked off the leaf or stem with your fingernail.
Relatively new to the United States, the European pepper moth is poised to cause significant damage to gardens and commercial agriculture.
Each time an invasive plant or pest is brought into an area, there’s no telling what might happen. Resident predators or local diseases may make short work of the interloper. Then again, the insurgent may find a rich, predator-free environment perfectly suited to a population explosion. We don’t know, yet, which way things will go for the European pepper moth, but it’s probably a good idea to know what we’re up against, just in case.
Plants damaged by European pepper moths
It’s difficult to get excited about something that hasn’t directly caused damage in your garden, so here’s the list of just some of the plants harmed by the pepper moth:
If that list doesn’t get your attention, I don’t know what will. Also on the list of favorite foods are roses, African daisies, azaleas, orchids, and many other flowers and ornamentals.
Damage caused by pepper moths
The moths themselves don’t cause any harm to plants. Like other moths and butterflies, it is the larval stage, or caterpillar, that feeds voraciously on leaves, roots, buds, fruit, and flowers. Pepper moth caterpillars may girdle young seedlings, causing what looks like damping off disease. Later larval instars may burrow into stems unnoticed, until the the stem collapses. Leaf damage starts out looking crescent-shaped, similar to damage by the Fuller rose beetle, or round, but the entire leaf ends up being eaten. Feeding is normally seen in the lower leaves, then moving up the plant until it is completed defoliated. Feeding on the roots can interfere with a plant’s overall health and vigor and feeding on buds, flowers, and fruit, well, there goes your crop. So, what does the European pepper moth look like?
Pepper moth identification and lifecycle
Also known as the European marsh pyralid, adult pepper moths (Duponchelia fovealis) have a wingspan of approximately three-quarters of an inch wide and a body less than half an inch long. The forewings are grayish-brown with two distinct yellowish-white transverse lines. The outermost line has a “finger” that points backwards.
At rest, the pepper moth holds its wings out to either side in a triangular shape. The head, body, and antennae are olive brown, and the abdomen features cream-colored rings. Legs are pale brown. Both sexes have long abdomens, but the male’s is unusually long, and he holds his curved upwards at rest.
Pepper moth eggs are really tiny (1/50 of an inch). The eggs start out whitish green or pale yellow, which turn pink, then red, as they mature. Just before hatching, the egg turns brown. Eggs are laid singly or in batches on the underside of leaves, normally near the leaf veins. Eggs can also be found on stems, at the crown, in the soil, on the tops of leaves, and even on greenhouse walls and furnishings.
Caterpillars start out salmon pink with a black head, and a line of grey and brown spots along each side. Some sections may feature a double row of dots. Using a hand lens, you can see a hair emerging from each spot. Just behind the head, you can also see a hard plate, which is the same color as the head. As they grow, the pink turns a dirty white color that can range from pure white to pale or even dark brown, depending on which of your garden plants they are eating.
These caterpillars can grow to over an inch long. Just before pupating, they may lose their spots. Pepper moth caterpillars create a cocoon out of soil, frass, and webbing. The cocoon can be 1/2 to 3/4 of an inch long.
A single female pepper moth can lay up to 200 eggs. Under optimal conditions (temperatures around 68°F), those eggs can hatch in 4 to 9 days. Over the next 3 or 4 weeks, the caterpillars feed ravenously. Then, pupation takes 1 or 2 weeks. Adult moths live to mate and procreate for a week or two and the whole process beings again. In greenhouse environments, 8 or 9 generations a year can occur. That ends up being a lot of pepper moths! In areas like California, where cold winters rarely occur, this pest could prove to be devastating.
These moths have an unusual flight pattern - both males and females fly fast and low, with their abdomens curved upwards. You may see individual moths, or they may swarm. Pepper moth caterpillars are photophobic, which means they do not like light. If you shine a flashlight on a pepper moth caterpillar, it will become agitated, moving rapidly side to side.
How the pepper moth got here
Pepper moths have been present in Europe for a very long time. In 1984, it became a greenhouse pest in Europe and Canada for the cut flower, vegetable, and aquatic plant industries. It is believed to have been spread globally through infested plants from those products. [Yet another example of why it is so important to quarantine new plants!] By 1988, the pepper moth had developed a taste for strawberries. In 2004, the pepper moth was found on begonia plants in San Diego, CA. It was again detected in 2010. By 2011, the European pepper moth had been found in seventeen California counties, as well as in fourteen other states. Departments of Agriculture in each of these states is monitoring for this pest. If you think you see one, please try to capture it and report it to your local County Extension Office.
Native to Europe, the pepper moth moth prefers fresh and saltwater marshes. You might think, since you don’t have a marsh in your garden, that your plants are safe. But most of us have a creek, reservoir, or some other body of water nearby, and a pepper moth can fly up to 62 miles.
Also, check the debris (detritus) that falls from container plants and around the base of the containers for signs of eggs or pupae. You can also lightly brush the soil around potentially infested plants for signs of pupae and cocoons.
How to control European pepper moths
At this point, the best biological controls are to spray Bacillus thuringiensis (Bt) or beneficial nematodes (Heterorhabditis bacteriophora and Steinernema spp.). Rove beetles seem to enjoy feeding on pepper moth eggs and caterpillars, and certain predatory mites and wasps also parasitize these pests, so avoid using broad-spectrum pesticides. Since pepper moths prefer moist, hidden areas, keeping your garden tidy and free of overly moist areas can reduce the chance of perpetuating the species in your neck of the woods.
Again, because this is a relatively new pest, with the potential for significant long term damage, if you see one, please report it. If you live in California, you can call 1-800-491-1899. If you live elsewhere, contact your local Department of Agriculture for reporting instructions. Knowing where this pest is can help in its eradication, which is really good news for your tomatoes, basil, figs, and cucumbers!
You can grow a surprising amount of food in your own yard. Ask me how!