Selenium (Se) is a plant nutrient that easily falls into the “too much of a good thing can be a bad thing” category.
If you grow a lot of your own food and your soil lacks selenium, you might, too. In fact, selenium deficiencies are a global dietary problem. On the flip side, if your soil has too much selenium, it can make you very, very sick.
People and animals must have a little selenium to be healthy. The same is true of some plants. Let’s see what selenium does, which plants use it, and how to tell when there’s too much selenium in the soil.
How plants use selenium
Selenium isn’t considered an essential plant nutrient. For some plants, such as poplar trees, selenium is useful. Selenium is believed to stimulate plant growth and to counteract stress, pests, and disease. [In the human body, selenium makes antioxidant enzymes that prevent cell damage.]
Plants grown on selenium-depleted soils end up being less nutritious for us. The Pacific NW, New England, the Great Lakes, and certain areas around the New Mexico and Arizona state line are traditionally low in selenium. But, as we all know, each yard has its own characteristics.
You won’t see selenium listed in a soil test report unless you specifically ask for it. The presence of certain weeds and other plants may. In some cases, high selenium levels are needed for growth. These plants will accumulate toxic levels of selenium in their tissues. These plants are referred to as obligate and include:
Facultative selenium accumulators do not need selenium to grow, but will accumulate it anyway:
Most other plants are referred to as passive selenium accumulators. These plants can absorb too much selenium and suffer toxicosis. This is especially true for grasses and cereals, such as barley.
Toxic soil can be corrected with something called phytoremediation. Phytoremediation takes advantage of the fact that some plants absorb toxins through their roots. Before plants can cough those toxins into the atmosphere through their stems and leaves (transpiration), the plants are harvested and disposed of safely.
Signs of selenium toxicity
Selenium toxicity appears as stunting, early leaf death, and chlorosis. Leaves of affected plants may wither and dry up. High selenium levels in the soil can also cause copper, iron, and zinc deficiencies. Of course, these symptoms can mean several other things, as well. You will have to consider symptoms, location, and the presence of the aforementioned plants in your analysis.
Too much selenium in the soil can make your edible plants toxic. This can be the result of native bedrock. It can also be caused by industrial runoff. If you suspect high selenium levels in your soil, contact your local County Extension Office or Department of Agriculture.
Mites and spider mites are garden pests. They suck the life from your plants and spread disease. Unless they are predatory mites. Predatory mites are our allies, though you may never see them without a hand lens.
Predatory mite description
Generally speaking, predatory mites are pear-shaped and translucent. They may also be white or the color of their prey, usually reddish or brown. Nymphs look like tiny adults with the same coloration. Wedge-shaped eggs are clear or white.
Some predatory mites are smaller than others. The Western predatory mite (Galendromus occidentalis) weighs in at only 1/70th of an inch in length (0.36mm). This means you could line up almost 50 of them, end-to-end, across an American dime. But don’t let their size fool you.
Predatory mite species
Predatory mites may be incredibly small, but they can take a serious bite out of your mite (Eriophyidae) and spider mite (Tetranychidae) problems. There are hundreds, perhaps thousands, of different types of predatory mites. They are grouped into one of four categories:
Different species have different favorite meals, so you can customize your protection with just a little research.
Predatory mite lifecycle
The life of a predatory mite is short. Once the eggs hatch, they quickly go through a 6-legged larval stage and two 8-legged nymph stages before reaching adulthood. In her 30-day life, an adult female predatory mite will lay up to 21 eggs on the underside of leaves, in flowers, and within the crevices of buds. Depending on the weather, those eggs will hatch in 1 to 4 days. There can be up to 10 generations each year.
It is difficult to know if predatory mites are present because of their size, but you can buy them. They will help protect your avocado, citrus, grape, plum, strawberry, and many other crops. Before you release your predatory mites, be sure to reduce dust in the area by giving everything a quick rinse with the hose. You’ll want to avoid broad-spectrum pesticides and miticides, as well.
Miticides kill mites and protect rhinos. I’ll get to the rhinos in a moment.
When temperatures are high and humidity is low, mite populations can quickly get out of hand. They suck the life from your garden plants, reducing crop sizes, and making plants more susceptible to other problems.
Miticides are also known as acaricides. These pesticides specifically target members of the arachnid subclass Acari. If your garden plants are suffering from infestations of mites or spider mites, you may want to consider using miticides. Or you may not.
Researching various miticides for this post, I ran across some very hard to pronounce words and some scary warnings. I started to list the most commonly used miticides, their targets and toxicities and realized it made for tedious reading (and writing). Bottom line: not all miticides are safe to use on edible plants. Many of these chemicals are dangerous to beneficial insects, honey bees, and us. Whenever using chemical treatments, be sure to read the label completely and follow the instructions.
Organic mite control
Diatomaceous earth (DE) can also be used against mites and spider mites. It desiccates them and kills them without leaving any chemical residue. Other food-grade dusts that also kill these pests without chemicals. These other dusts have an advantage over DE in that they do not contain silica. Breathing in silica dust is bad for us, too.
There are also predatory mites that prey on mites and spider mites.
Whichever treatment you decide to use, don’t apply it on a windy day. It and your money will simply fly away on the breeze. To be effective, sprays and dusts must coat the underside of all the leaves affected by mites or spider mites.
Now, about those rhinos
Rhino poaching is being deterred by drilling holes in the horns of sedated rhinos and packing those holes with miticides. It doesn’t hurt the rhinos, but it brings on nausea, diarrhea, and convulsions in anyone who eats the horn, thinking it will provide them with some magical powers. And it won’t kill them. I think it’s the least punishment they should have to suffer for needlessly killing an endangered animal, don’t you?
This word may not help you grow better tomatoes, but it is relevant. I found it interesting and I hope you do, too.
No one knows where the word strig came from. In England, strig refers to the thread that holds a button to your shirt. It also refers to the tang of a sword blade. In the plant world, strig refers to the footstalk or pedicel of flowering or fruit-bearing plants, such as currants. A type of peduncle, these tiny stems occur within flower clusters or inflorescences. They provide support for the individual florets. The flowers that grow from a strig are called a sessility.
Female hops flowers are cone-shaped blooms called strobiles. If you sliced one of those flowers in half, you would see a central stem. That central stem is known as a rachis or strig. This strig is what attaches the flower to the bine or pedicel.
If you open up a fresh fig, you will see lots of hair-like structures. Those are male and female flowers held up with strigs.
While adult pea leaf weevils (Sitona lineatus) are chowing down on the leaves and growing tips of your legumes, their miscreant offspring are underground, gnawing away at the nitrogen fixing nodules found in and around the root system. Originally from Europe, pea leaf weevils are now found around the world.
How can you tell if pea leaf weevils are attacking your plants, and what can you do about it?
Pea leaf weevil damage
Scalloped leaf edges and gnawed-off stumps where growing tips used to be are the first signs that these invasive pests have reached your garden. Leaf scalloping tells you that adult pea leaf weevils are feeding. What you can’t see without digging up the plant is all the damage being done to the root nodules. Larval feeding can completely halt nitrogen fixation, resulting in stunting, chlorosis, and plant death. All legumes are susceptible to pea leaf weevil feeding, though lentils are less likely to be affected. I have no idea why. Larvae may also burrow into young pea pods and start feeding on young peas.
Pea leaf weevil identification
Pea leaf weevil adults are one-fifth of an inch long, grayish-brown, and rather slender in physique. If you look closely, you may be able to see three pale lengthwise stripes down the thorax. Larvae are milky white with a dark head. Like other grubs, they tend to hold themselves in a C-shape. These larvae have no legs and are about the same size as adults. Eggs are white at first but turn nearly black just before hatching.
Pea leaf weevil lifecycle
These pests tend to have one generation each year. After overwintering in protected feeding grounds, adults fly and walk to new territories where female pea leaf weevils will lay 1,000 to 1,500 eggs on or near young legume plants. When those eggs hatch, the larvae enter the soil where they go through five developmental stages or instars. They feed heavily on the nodules that allow legumes to convert atmospheric nitrogen into a form they and neighboring plants can use for food. While these pests feed on all legumes, they only reproduce on peas and fava beans.
Pea leaf weevil management
Commercial growers apply insecticidal seed treatments before planting, but that’s probably not an option for the home grower. The good news is that black clock beetles, ground beetles, and rain beetles all love to eat pea leaf weevils. By mulching and applying aged manure and compost around your legumes, you can encourage these beneficial insects. This will also provide your legumes with any nitrogen they may need.
As always, avoid using broad-spectrum pesticides. Those chemicals end up killing off all your helpers. Bacillus thuringiensis (Bt) can also be used against these pests, but it only works on the weevils it touches. Eggs and larvae will be unaffected. These other tips can help protect your peas and other legumes from pea leaf weevil damage:
I hope that pea leaf weevils never find your garden.
I thought I saw a whitefly on my apartment windowsill, but I was wrong. It was a dustywing.
Unlike whiteflies, which can carry diseases and suck the sap from your garden plants, dustywings are beneficial predators. They prey on slow-moving invertebrates, such as aphids, mites, and scale insects. They also eat arthropod eggs, including corn earworms, mealybugs, and tomato hornworms.
These net-winged hunters are very tiny. Their wingspan can range from one-twentieth of an inch up to one-fifth of an inch wide. They are covered with a whitish or grayish powdery wax. They secrete that wax from glands on the abdomen, head, and thorax. [Imagine being able to create your wardrobe that way!] They have tan-colored translucent wings and short antennae. Eggs are oval, yellowish-pink to orangish, and somewhat flattened. Larvae are red and white.
Dustywings are commonly found around woody plants. They are mostly active at dusk (crepuscular) and attracted to lights. Each female can lay up to 200 eggs. These eggs are laid singly on nearby leaves and on the bark. There are two generations each year. Each larva goes through four instars. And all that growing requires a lot of food. A single dustywing larva was recorded as eating 226 red mites. That’s what I call helpful!
You can encourage dustywings to stay in your landscape by providing woody shrubs for them to live in and avoid using broad-spectrum pesticides. Have you seen dustywings in your garden? I released mine into the Seattle wilderness.
Do your cucumbers, melons, squash, and watermelons have spots? Do your pumpkins have warts? It may be papaya ringspot.
Papaya ringspot wiped out 94% of the papaya crops grown on Oahu back in the early 1960s. As a result, papaya production was moved, under quarantine, to the Big Island of Hawaii. As is often the case in these situations, the virus found its way there, again devastating the papaya industry and homegrown papaya trees. More moves and more quarantines occurred, but it wasn’t until resistant varieties were developed that papayas could be grown successfully. That might be the end of the story, but it’s not
The papaya ringspot virus (PRSV) mutated, traveled, and expanded its diet to include several common garden plants. These include members of the squash family, tree spinach (Chenopodium amaranticolor, aka C. giganteum), peas, castor beans, and quinoa (C. quinoa). Currently found in the U.S., Europe, India, the Middle East, and South America, it is safe to say that papaya ringspot falls under the plant pandemic category.
Papaya ringspot symptoms
Like many other viral plant diseases, papaya ringspot looks like infected cucumbers and melons have developed measles. A mosaic of scattered dark green or intense yellow spots appears all over the fruit surface. Blisters may also be seen. Leaves of infected plants are chlorotic and distorted and may develop shoestringing. Stems and petioles may have oily streaks. This disease looks a lot like watermelon mosaic. In both cases, infected plants should be removed and tossed in the trash.
Papaya ringspot lifecycle
This virus congregates around the mouths of aphids, never actually entering the pest. As the carrier aphid feeds on sap, the virus moves from the aphid’s face to the plant’s veins. Wouldn’t that make an interesting video?
The papaya ringspot virus can also travel on seeds and seedlings.
Papaya ringspot prevention
There is no cure for papaya ringspot, and it can spread to neighboring healthy plants. Quarantining new plants and investing in certified pest- and disease-free seeds and seedlings are the best ways to prevent the papaya ringspot virus from attacking your garden.
Your lawn may be harboring a plant pandemic that’s killing your corn. That disease is called barley yellow dwarf (BYDV). More than 20 different aphid species spread this viral disease, and it is found around the world.
Barley yellow dwarf host plants
Barley, corn, and the ryegrass and fescue in your lawn are not the only plants that can become infected with this disease. All members of the grass family (Poaceae) are susceptible.This means that your millet, oats, rice, rye, ryegrass, sorghum, sugarcane, and wheat can also become infected with barley yellow dwarf. It is the costliest disease worldwide of all cereal crops.
Barley yellow dwarf symptoms
This disease is tricky to identify. It looks similar to root and crown diseases, nutrient deficiencies, environmental stresses, and wheat streak mosaic. Closer inspection of unhealthy-looking patches in your lawn or grass family crops may reveal purple, red, orange, or yellow discolorations. These discolorations are seen from the tip downward and from the edges to the midrib. Infected leaves are often shorter, stiffer, and more upright than healthy leaves. Stunting is common due to shortened internodes. You may also see serrations along leaf edges and some infected plants start growing into a corkscrew shape.
Barley yellow dwarf prevention
Fungicides are ineffective against barley yellow dwarf. Instead, good cultural practices are your best plan of attack. Since aphids are the vectors for barley yellow dwarf, planning your planting schedule around aphid migrations can help reduce the likelihood of disease occurring. I know that aphid migrations aren’t usually mentioned on the evening news. But regularly monitoring your plants for aphids will make it very clear when they arrive and start reproducing. Planting seeds at times when aphids and seedlings are less likely to occur at the same time will help reduce disease. These other tips will also help keep your garden plants healthy:
Black citrus aphids (Toxoptera citricida) are vectors for citrus sadness, a potentially fatal disease of grapefruit, lime, lemon, and orange trees. They spread this disease as they feed on the sap found in new leaves and tender buds. And that feeding causes damage of its own, weakening trees, stunting growth, and generating honeydew. That honeydew provides the perfect growth medium for sooty mold and other fungal diseases, which block photosynthesis. Black citrus aphids are considered one of the world’s most serious citrus pests.
Originally from southeast Asia, this pest is now found in Africa, Australia, India, and Central and South America. In 1995, black citrus aphids appeared in Florida, where they are now well established. It is estimated that these pests will devastate the California citrus industry if they find their way across the Rockies. This is one reason why you have to wait in line at the agricultural inspection stations when driving across some state lines.
Black citrus aphid identification
Also known as oriental citrus aphids and brown citrus aphids, they get the different color names because they change color as they develop. Adult black citrus aphids are black and shiny. Like other aphids, they can be winged or wingless. Nymphs are reddish-brown. And there are no eggs unless they live in Japan.
Black citrus aphid lifecycle
All black citrus aphids are female, and all of those females give birth to live young unless they live in Japan. For some bizarre reason, black citrus aphids occurring in Japan do lay eggs. In either case, those populations can explode in record time. It is estimated that a single black citrus aphid can produce more than 4,400 offspring in three weeks. Those offspring can start reproducing on their own when only one week old. You can see how things could quickly get out of hand. The network effect of all that reproduction can result in 600 billion aphids in a single season, all starting with one aphid.
Managing black citrus aphids
One way to reduce aphid problems is to only feed nitrogen to plants at the appropriate times and avoid shearing citrus trees. Shearing and nitrogen both stimulate vulnerable new tip growth. Also, ants protect aphids. You can eliminate that protection by wrapping the trunks of citrus trees with sticky barriers. You can also use sticky sheets hung in your citrus trees to monitor for winged aphids and other pests.
Natural predators, such as ladybugs, and parasitic wasps will help reduce aphid populations. You can attract these beneficial insects to your garden by installing insectary plants, providing water, and avoiding the use of broad-spectrum pesticides.
A powerful stream of water from your hose can dispatch large clusters of aphids which are then unable to return to the tree, but this treatment won’t get them all, and it only takes one. Insecticidal soap can also be used, but that treatment is only effective on the aphids it touches.
Monitor your trees regularly for signs of black citrus aphids and report any potential sightings to your local County Extension Office right away.
Citrus sadness is not a case of lemon tree depression. But citrus growers around the world are pretty sad about this plant pandemic.
Citrus sadness, more scientifically known as citrus tristeza virus (CTV), is the costliest citrus virus. It has killed more than 80 million citrus trees and made an added 40 million more citrus trees useless for growing edible fruit. And it spreads quickly.
First seen in South America in the 1930s, this disease was called “tristeza” which means sadness in Spanish and Portuguese. Citrus sadness attacks several citrus species and passion flowers (Passiflora gracilis).
Symptoms of citrus sadness
Symptoms of citrus sadness vary depending on the infected plant species. They are generally grouped into one of three categories: decline, seedling yellows, and stem-pitting. In each case, viruses populate the phloem, causing chlorosis, vein clearing, leaf speckling, fruit dwarfing, and stem dieback.
Decline can be fast or slow. It presents as chlorotic leaves and stem dieback. Citrus sadness decline may take only days to kill a mature tree (fast), or it may take years (slow). In the case of slow decline, infected trees often exhibit a bulge just above the graft. Decline is most commonly seen in grapefruit, mandarin, and sweet orange trees.
Seedling yellows most commonly affects lemon, pomelo, and sour orange. This type of citrus sadness causes overall yellowing and dieback.
Stem-pitting is the most virulent form of citrus sadness. It most often infects sour orange, a variety commonly used as rootstock for several other citrus species. [Which rootstock is your orange tree grafted onto?] Symptoms of stem-pitting match its name: pits form along the trunk and branches. This damage reduces crop yield and weakens the tree, making it susceptible to other diseases and pest damage.
Citrus sadness prevention
Citrus sadness is spread by aphids, especially brown citrus aphids and oriental citrus aphids. As you probably already know, controlling aphids is an ongoing battle. Aphids can have wings, and they reproduce at mind-boggling rates. As much as possible, monitor and treat for aphids. And be sure to buy certified disease-free and disease-resistant rootstock. And if you wrap tree trunks with sticky barriers, ants will be unable to protect aphids from their natural predators.
If you suspect citrus sadness has found its way to your tree, contact your local County Extension Office right away.
Nobody wants scabby cucumbers, squashes, or melons, but sometimes it happens.
Cucurbit scab goes by several other names, some of them quite colorful: cucumber gummosis, cucumber leaf blight, cucumber spotting, cucurbit fruit blight, gray anthracnose of cucurbits (even though it’s not a type of anthracnose), and, my favorite, cucurbit pox.
I can hear it now, as Renaissance Faire washerwomen throw insults and dirty undergarments at the crowd: “A pox upon thy cukes!” Of course, I would never wish a pox upon anything in your garden, so let’s see what we’re up against with this one.
The what and when of cucurbit pox
This disease affects nearly all members of the cucurbit family. This means cantaloupe, gourds, honeydew, summer and winter squash, and pumpkins are all susceptible. For some reason, watermelon is rarely affected. I don’t know why.
Cucurbit scab is a fungal disease of the squash family caused by Cladosporium cucumerinum. This disease thrives in areas with cool, moist weather and becomes a serious problem when temperatures are between 57°F and 77°F. Moisture can be from heavy dew, frequent fog, or light rain.
Cucurbit scab symptoms
Cucurbit scab is found around the world. Symptoms can vary quite a bit, depending on where it occurs. Generally speaking, this disease presents as dark, olive-colored, velvety lesions on the surface of cucurbit fruits. Those lesions may also be brown or black. They are usually sunken and one-eighth of an inch in diameter. These lesions occur because of the pathogen’s ability to break down pectin and cellulose. A gummy substance may ooze from these lesions. As they mature, these spots get darker and sink into the fruit, creating holes loved by fruit flies and other pests. These pits can merge into rotted areas up to two inches across. In more resistant varieties, these lesions evolve into hard, warty structures.
Infected leaves have pale green, water-soaked areas that fade to gray. These areas may have a yellow halo. From a distance, it may look like powdery mildew. Closer inspection shows that these areas are distinctly triangular, hence the anthracnose assumption. These dead areas dry and fall out, leaving plants looking quite ragged. Cucurbit scab can also shorten the internodes, making plants look stunted.
Cucurbit scab management
Prevention is your first line of defense with any disease. Buying certified disease-free seeds, seedlings, and mature plants can help keep spores out of your landscape. Spores are spread by insects, tools, clothing, splashing rain, and the wind, so you’ll still have to be on the lookout.
You can prevent cucurbit scab from occurring with some simple cultural practices:
I hope this information helps you keep your cucurbits healthy and productive.
You can grow a surprising amount of food in your own yard. Ask me how!
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