Garden Word of the Day
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Beet Yellows Viruses
If you grow beets or spinach, you should probably know about beet yellows virus (BYV) and beet pseudo yellows virus (BPYV). These two diseases look and behave enough alike that you really don’t need to know the difference, unless you start working in a plant disease lab. [I’d love to hear about that job!]
Along with BYV and BPYV, beet chlorosis virus and beet western yellow virus are two other diseases that can be included in this group for our purposes. [Unfortunately, I was unable to find a photo I could use. Do you have one?]
Symptoms of beet yellows viruses
Unlike the beet mosaic virus, where symptoms are first seen in new, younger leaves, symptoms of beet yellows viruses first appear on lower, older leaves. That yellowing is seen between the veins. If you look closely, you may also see reddish-brown spots. Those spots are like freckles, eventually becoming so numerous as to create bronzing. As the disease progresses, leaves thicken, becoming leathery and brittle. Of course, your beet plants can catch both diseases, or more, in a condition called virus decline, which can make diagnosis tricky.
These diseases are all spread by aphids. Aphids are bad. Aphids are the most common guilty parties when it comes to disease transmission. As they travel around your landscape, aphids pierce pretty much every plant they come across, looking for a tasty meal. Each time they do, viruses can move from the aphid to your plants. And beets aren’t the only plants that can become infected with beet yellows viruses.
Beet yellows viruses have can infect raspberries, strawberries, melons and squash, and members of the sunflower family. That’s probably half the edibles growing in your garden! Poppies can catch these diseases, too. So, what can you do about it?
Controlling beet yellows viruses
It only takes a single aphid to explode into a problem. They reproduce rapidly and don’t need help from another aphid to start making baby aphids. Beet yellows virus problems often begin in overwintered beets and other host plants. Cutting host plants off at soil level at the end of the growing season allows valuable soil microorganisms to migrate to other plants and you may even get new crops come spring! [I have found this is particularly true of cabbages, Brussels sprouts, broccoli, and Swiss chard.]
These tips can help reduce the risk of beet yellows viruses occurring in your garden:
Any time you start seeing leaf discoloration, take a closer look. It’s usually easier to control problems sooner rather than later.
Shoestrings are no surprise on your sneakers. Finding them in the garden is something else.
Leaves and stems grow in predictable ways, except sometimes they don’t. Sometimes stems grow strangely flattened in a behavior known as fasciation. If you see leaves or other growths that look like a Halloween hag's broomstick, then it's witches broom. But when leaves grow oddly thin and leathery, it is called shoestringing. There are several types of shoestringing, and they have different causes and cures.
Temperature-based shoestringing is a disorder commonly seen on eggplant leaves. At first, you would see holes in the middle and on the edges of leaves and think it was insect feeding. As the condition worsens, you might suspect it was a viral disease or chemical overspray. In severe cases, you may see chlorosis or stunting. This type of shoestringing occurs when high temperatures occur as plants are in specific growth stages. In other words, there is nothing you can do. You should still probably monitor for insect pests, just in case.
Chemical overspray can also cause shoestringing. A neighbor (or you) may spray herbicide on a breezy day. Chemicals soar over the fence (or across the yard) and land on your tomatoes or other crops, causing leaves to become thin and stringy. The same symptoms may also indicate viral disease.
Cucumber mosaic virus (CMV) can cause shoestringing in tomato plants. Are the leaves mottled? Take a closer look at the stems. If you see a zigzag pattern, it is CMV.
Blueberry plants are susceptible to a virus that causes shoestringing. Symptoms are not visible at first. This disease lays dormant for up to 4 years before long red streaks appear on stems. Those streaks are more frequent on the side of the plant that gets the most sunlight. Leaves take on a reddish or purple straplike or cupped shape. Rather than deep purple, infected fruit has more of a reddish tinge. Healthy white flowers develop a pink tint. Spread by blueberry aphids, this disease is highly contagious. Remove infected stems and monitor the plant closely.
Armillaria root rot is another viral shoestringing disease. Also known as shoestring rot, this disease affects several fruit and nut trees. Rather than growing normally, infected leaves cup downward and start yellowing. If you were to dig up the roots of a tree infected with Armillaria root rot, you would see blackened rhizomorphs, or shoestrings, growing on the surface of otherwise healthy-looking roots. In some cases, those shoestrings may grow up under the bark. And sometimes, they glow! Sadly, trees infected with Armillaria root rot must be removed.
If you see shoestringing in your garden, look again. See if you can figure out what's causing it.
Apple Clearwing Moths
Have you ever seen strange bits sticking out of your apple tree in spring?
Or, moths fluttering around your tree on a summer afternoon? You might want to take a closer look. Those bits may be discarded pupal casings from apple clearwing moths, and these pests can kill your tree.
Also known as red-belted moths, apple clearwing moths (Synanthedon myopaeformis) are native to Europe, North Africa, and the Near East. They were first seen in North America in 2005, in Canada. Now, Canadian entomologists estimate that the majority of host trees in British Columbia are infested. By 2007, these pests had made their way to Washington state. It’s only a matter of time until they spread further.
And apple trees aren’t the only ones vulnerable to this pest. If you grow almonds, apricots, cherries, crabapples, peaches, pears, plums, or quince, you should know about apple clearwing moths. These invasive pests also attack hawthorn and mountain ash trees and are attracted to showy milkweed plants.
Damage caused by apple clearwing moths
The moths themselves are harmless. It’s their larvae that cause significant damage, especially to older trees. Caterpillars burrow under the bark, entering at burr knots, grafts, pruning wounds, injured branch collars, and areas damaged by tree supports left in place for too long.
Larval feeding can kill young trees. Trees that survive often have weakened limbs, reduced fruit set, and early leaf drop. These conditions make trees susceptible to other pests and diseases and more vulnerable to drought stress and frost damage.
Apple clearwing moth lifecycle
These pests have a 2-year lifecycle. Female moths feed on nectar early to mid-summer, laying up to 250 eggs singly in crevices. When the eggs hatch, larvae burrow into the cambium layer. They feed on sap found in the phloem for the next two years. As they eat, they create shallow, winding galleries that weaken the tree. They also feed on new leaf and flower buds. In spring, you may be able to see the frass (bug poop) pushed out of these galleries by the larvae. [How about that? Even insects perform spring cleaning.]
Larvae spend the winter protected in these tunnels, pupating the next spring. When pupae are ready to break free and fly, they push themselves through these frass openings. In addition to these discarded pupal cases, you may also see tiny holes (about half the diameter of a pencil lead) around the base of an infested tree.
Apple clearwing moth description
It should come as no surprise that clearwing moths have transparent wings. Unlike most moths and butterflies, clearwing moths do not have scales on their wings. They do have short, bushy tails, though!
Apple clearwing moths have narrow, bluish-black bodies. Their forewings are slender and their hindwings are short. They have wingspans of ¾ - 1” wide and distinct reddish-orange bands around their bellies. Larvae are ½- ¾” long, a dirty white color with a reddish-brown head. Pupae are ½” long and pale yellowish-brown.
Apple clearwing moth control
Preventing this problem is much easier than fixing it. Start by making sure your pruning cuts are clean and flat and that they do not cut into the branch collar.
If you believe your trees have become infested with apple clearwing moths, do not use wires to probe the holes the way you might go after squash vine borers in your zucchini plants. Infested trees already have enough damaged areas. They don’t need more.
You may be able to reduce the number of adult moths emerging from cocoons by spraying Bacillus thuringiensis (Bt). Applications of cottonseed oil have also been shown to be helpful.
You can use the same yellow pheromone traps that attract male peach tree borers or make your own traps by baiting bottle traps with grape juice. To make a bottle trap, simply cut the top off a liter soda bottle and invert the top into the base. Tape the two parts together, creating a funnel. Male and female clearwing moths will be attracted to the grape juice but unable to find their way out of the trap. A mix of 8 parts water, 1 part apple juice, 1 part vinegar, and a little sugar has also been shown effective.
Just remember, if you put out attractants, whether food or pheromonal, you will be attracting moths to your garden. There are insecticides rated for use against apple clearwing moths, but they have their own drawbacks. Only do these things if you need to.
If you believe you have apple clearwing moths on your property, please contact your local County Extension Office right away. And try to capture a specimen.
If you have black mold in your house, you should go outside right away.
Garden variety black molds are something else entirely. Well, mostly.
Mold of any color
Molds are a type of fungus. Other common fungi include yeasts, mushrooms, and truffles. Fungi do not contain chlorophyll, so they do not perform photosynthesis. Instead, they get their food by breaking down and absorbing organic materials. Fungi reproduce using spores and many of them generate threadlike filaments, called hyphae. These hyphae develop into a complex network, called the mycelium. Despite all the similarities, slime molds, such as dog vomit slime mold, are not fungi. We’ll leave that discussion for another day.
You may see gray mold, white mold, black, or even blue mold. There are several different types of black mold. All of them produce black mycelium. Most of them are relatively benign, but some of them are dangerous.
Toxic black mold
After building materials are exposed to moisture from flooding or fire-fighting, Stachybotrys chartarum fungi start to grow. Generally rare in nature, these spores can also be found in grain and soil. Water-damaged buildings provide the perfect habitat for these microfungi to breed and grow. As they grow and are disturbed, they release toxins into the air that can make you sick. Toxic black mold needs to be removed right away.
Sooty mold is another black mold. Often seen on citrus and other tree leaves, onions and garlic, peanuts, and grapes, this black mold is the Aspergillus niger fungi. For the most part, this variety is safe to be around, unless you are a farmworker and exposed to it alot. In that case, a serious lung disease called aspergillosis can occur. This fungus can also cause fungal ear infections (otomycosis).
I was surprised to learn than the sooty mold fungus is commonly used in industrial applications to produce citric acid and high fructose corn syrup, and to clarify wine. Weird, right?
If you see sooty mold, apply sticky barriers to halt the protection provided by ants, and give your plants a wipe down to remove the mold.
Alternaria leaf spot
Also known as Alternaria rot and black rot, Alternaria leaf spot creates black or brown spots on the leaves of many garden plants. It can also create dark, round, flattened lesions on cherries, papaya, tomatoes, and many other fruits. Similar in appearance to blossom end rot, Alternaria leaf spot damage can appear anywhere on an infected fruit. [Unfortunately, I couldn’t find a photo I could use.] Exposure to the Alternaria alternata fungi has been found to trigger asthma and allergic rhinitis.
If this mold appears in your garden, your plants will benefit from proper spacing, pruning for better air circulation, and the removal of affected plant material.
Bottom line: If you see black mold, find out which type it is and take the appropriate action.
December is a time of skiing and sleigh rides in much of the northern hemisphere. Not so much in coastal California.
While iconic snowflakes rarely fall on my garden, your situation may be something else entirely. But, being from New England, I’ve seen my share. It wasn’t until very recently that I learned just how amazing each snow crystal really is.
Contrary to popular sentiment, bits of snow are not flakes. They are crystals. How these crystals form is mind-boggling. What it does to your garden may surprise you, too. But let’s start with a water molecule.
Most of us are familiar with H2O. That moniker tells us that each molecule of water is made up of two hydrogen atoms connected to one oxygen atom. It ends up that all those whirling electrons are pulled closer to the oxygen atom. This gives oxygen a slightly negative charge, leaving hydrogen atoms with a slightly positive charge. [Don’t run away! This will all make sense in just a moment.]
For snow crystals to form, water vapor, liquid water, and ice must all be present. As gazillions of water molecules float around in a cloud, their charges attract and repel each other like magnets. The negative side of a water molecule is pulled toward the positive side of other water molecules. [This is why water has surface tension, too.]
When snow crystals form, five more water molecules, in liquid form, collect on this negative side and end up creating a 4-sided pyramid, or tetrahedron.
As temperatures drop, this water turns to ice, suddenly shifting into the iconic 6-sided shape that decorates Christmas cards around the world. Up to this point, most snow crystals are identical. It’s when countless combinations of trajectory, humidity, and temperature changes are factored in that each snow crystal becomes unique.
[Did you know that snow crystals can form triangles, diamonds, and pillars? I didn’t either.]
Snow in the garden
If you wake one winter morning to see your garden blanketed in snow, don’t panic. While freezing temperatures can kill tender annuals, making a mess of leaves, a thick covering of snow protects plant roots, earthworms, and important soil microorganisms. Those chilling hours translate into bigger fruit and nut crops next year, too!
But how can snow crystals protect plants from freezing? It doesn’t make sense!
As temperatures drop, the water contained in plants expands as it freezes. This causes frost cracks in stems and blackened leaves. Snow-covered soil tends to stay right around 32°F. This happens because of tiny pockets of air caught within the 6-sided crystals. This air insulates whatever is covered. Of course, too much snow on tree branches can lead to breakage. You made need to prune or protect trees if you get a lot of the white stuff.
If temperatures happen to rise, well, plants get irrigated. Another surprising benefit is that nitrogen and sulfur in the atmosphere are captured as each crystal falls. When it melts, those important plant nutrients are released into the soil.
If snow falls on your garden this winter, take a cue from Nature and grab yourself a nice fuzzy blanket, a hot beverage, and start planning your spring garden!
Strawberries don’t grow on trees! Everyone knows that.
But you might be surprised, as my friend Linda was, to learn that you may already have this edible growing in your yard.
Strawberry trees are members of the heath or heather family (Ericaceae), making them cousins to blueberries, lingonberries, azaleas, and rhododendrons. Native to the Mediterranean region, these trees are often mistaken for manzanita and other ornamental landscape trees. The brightly colored, spiky fruits may not look edible at first glance. It ends up they don’t taste good when eaten too soon, either.
Strawberry tree fruit
Strawberry tree fruit has a bumpy surface and is about the size of a small walnut. These berries are sweet once they turn red, but not before. Even then, their taste is described as bland by some. Supposedly, Pliny the Elder gave this plant its name after saying, “Unum tantum edo.” (I only eat one) We don't know why. Maybe he didn't like it. Maybe he found the rich, custard-like texture of one fruit satisfying.
These fruits have tiny seeds which, to some, may make the fruit seem gritty, like a kiwifruit. My friend assures me that, once you’ve tried it, you’ll want to stand under the tree and keep eating!
So, why haven’t you seen these fruits in the grocery store?
Unlike apples and pears, which can be picked unripe and shipped and stored, strawberry tree fruit is very soft and it bruises easily. If you want strawberry tree fruit, you’ll have to grow your own tree or find a neighbor who already has one.
[I wonder how many other edible plants we know nothing about, simply because grocery stores can't sell them…]
How strawberry trees grow
These evergreen trees average 15’ tall and 10’ wide, but they can grow 30’ tall. The grayish-brown bark peels away, exposing a lovely reddish-brown inner bark, reminiscent of our beloved manzanita.
These trees grow best in USDA Hardiness Zones 7-10 and they love sunny, dry climates. Dark green, glossy leaves are 2-4” long and 1” wide, with red stems. White flowers appear in autumn, around the same time the previous year’s fruit is ready for harvesting.
Because the flowers are hermaphroditic, you only need one tree. These trees are moderately drought and frost resistant and can tolerate shade and salt. Like other family members, strawberry trees prefer neutral to slightly acidic soil.
Aphids and fungal leaf spot are the most common problems faced by these trees. Other potential pests include flathead borers, leaf miners, scale insects, thrips, and western tent caterpillars. Other diseases that may infect your strawberry tree include annosus root disease, anthracnose, Arbutus leaf spots, leaf galls, phytophthora, sudden oak death, and twig dieback. Many of these diseases can be prevented with good drainage.
Strawberry tree varieties
There are three different varieties of European strawberry tree: the Spanish Arbutus canariensis, the Greek A. andrachne, and the topic of our discussion today, A. unedo. There is a North America cousin, the madrone or madrone tree (A. menziesii), but the genetic connection is too distant to allow for easy hybridization. European cousins can cross-pollinate, but fruit production is intermittent to unlikely. One variety often found in California is a cross between A. unedo and A. andrachne. It is labeled Arbutus x Marina because of the San Francisco district where it was hybridized.
Strawberry trees can be grown from seeds or semi-hardwood cuttings. If you decide to grow a strawberry tree, local hummingbirds, butterflies, and birds will be glad you did.
You might, too. Thanks, Linda!
You can grow a surprising amount of food in your own yard. Ask me how!
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