You may have played with (or been horrified by) potato bugs as a child. The Colorado potato beetle is not that bug. [Those bugs are Jerusalem crickets, which are neither crickets nor from Jerusalem, but we will discuss those pests another day.]
The Colorado potato beetle looks more like a striped cucumber beetle. Unfortunately, the infamous Colorado potato beetle eats more than just potatoes. To make matters worse, this pest has an impressive ability to become resistant to even the harshest chemicals.
History of the Colorado potato beetle
The Colorado potato beetle (Leptinotarsa decemlineata) is also known as the ten-lined potato beetle, ten-striped spearman, or simply the Colorado beetle. First identified in 1824, this pest is native to southwest North America. Initially, this dome-shaped beetle preferred wild members of the nightshade family, but, by 1840, the domesticated potato became its favorite food, followed closely by tomatoes, peppers, and eggplants. Exports of potatoes (and the Colorado potato beetle) to France and Germany inspired the world’s first plant quarantine laws. During the Cold War, the CIA was accused of releasing Colorado potato beetles in Russia, in an effort to threaten the Soviet Union’s food supply. In 2014, to call a pro-Russian separatist of the Ukraine a ‘koloradi’, a nickname given to the invasive Colorado potato beetle, was an insult directed at their similar orange and black stripes. In Hungary, a statue commemorates the arrival of this difficult to control pest.
Colorado potato beetle description
This stubby, round beetle has the same size and shape as a Japanese beetle. It is usually 1/ to 1/2 an inch long and tends to be bright yellow or orange, with five stripes on either side of its wing covers (elytra) and scattered holes (elytral punctures) on its shoulder covers (thorax). Colorado potato beetles are easily confused with their close cousins, false potato beetles. False potato beetles, L. juncta, have stripes, too, but their stripes tend to be white, with light brown center stripes, and their elytral punctures are spaced in an orderly fashion.
Colorado potato beetle lifecycle
Adult females can lay over 500 eggs in one month. These bright yellow or orange, torpedo-shaped eggs are laid in clusters on the underside of leaves. These beetles go through four stages, or instars, on their way to adulthood. Each instar only lasts 2 or 3 days. Eggs hatch after 4 to 15 days, depending on temperature. These larvae have humped backs, are dark reddish brown, with two rows of spots on either side (if you look very closely). They can usually be found near abandoned egg cases. By the time these baby beetles reach their third instar, they are bright red with black heads. These pests will continue feeding and growing until they reach adult size. Then, during the fourth instar, they enter a nonfeeding, prepupal stage. These larvae are a lighter color and they don’t move around very much.
Natural predators, such as ladybugs, pink lady beetles, spiders, ground beetles, lacewings, wasps, damsel bugs, beneficial nematodes, and praying mantids all enjoy feeding on these pests, so avoid using broad spectrum pesticides.
Neem oil and Bt sprays can be used as effective controls. Dusting with diatomaceous earth (DE) has also been shown to be effective.
Black rot may sound like the perfect name for your next Halloween character, but this bacterial disease can wreak havoc on plants in the cabbage family (Brassicaceae).
Popular brassicas, or cole crops, include broccoli, cauliflower, kohlrabi, horseradish, Napa/Chinese cabbage, collards, turnips, rutabagas, Brussels sprouts, watercress, kale, radishes, bok choy, and mustard. Rapeseed (canola) is also a member of this family. And all of these plants are susceptible to black rot, a close cousin to bacterial spot.
Black rot symptoms
The early symptoms of black rot (Xanthomonas campestris pv. campestris) don’t look like anything serious. You will see some chlorosis (yellowing) along leaf edges (margins), and some V-shaped lesions pointing toward the center of the plant. Then, those lesions may dry up and fall away, lulling you into thinking the problem has resolved itself.
Instead, black rot bacteria have gained a foothold in the phloem and xylem of your cabbage. As they populate and block these important vascular tissues, wilting and dieback occur.
If you cut an infected stem longitudinally, you will be able to see blackening of the vascular tissue. [Just be sure to disinfect your cutting tool afterwards, so that you don’t spread the disease to other plants.]
Managing black rot in the garden
Since this disease is most likely to occur in warm, humid weather, planting your cole crops after any chance of Indian summer has passed can help prevent it from occurring. The moisture left behind from overhead watering can also create the perfect conditions for black rot to take hold, so water your cabbages at ground level. There are some resistant varieties available, so shop for those if you have had problems with black rot in the past. Also, it’s a good idea to use crop rotation with cabbages and cauliflower in particular, as these two crops are the most likely to be affected. Since this bacteria can survive on cruciferous weeds, be sure to keep your cabbage patch weed free.
Glyphosate is an herbicide. It is the active ingredient in RoundUp and other popular broadleaf weed and grass killers. And recent scientific research has shown us that glyphosate may be killing honey bees along with plants.
Before we begin learning about this litigious herbicide, let me tell you from the gate that I do not use it, in any form. I practice sustainable, integrated pest management (IPM) and organic gardening. This is a heated topic and I want you to be aware of where I stand.
The chemistry of glyphosate
Glyphosate is a broad-spectrum, systemic herbicide, which means it is absorbed by and kills the plants it touches. It does this by blocking an enzyme pathway, called the shikimic acid pathway. [It gets this unique name from the Japanese shikimi flower, in which the process was first identified, back in the 1800s.] The shikimic acid, or shikimate, pathway is a 7-step metabolic process that synthesizes folates and amino acids necessary for plant survival. Herein lies the problem. The shikimic pathway is also used by algae, bacteria, fungi, protozoa, and others. When the shikimate pathway in any of these organisms is blocked, they die.
Glyphosate in the environment
More that 700,000 tons of glyphosate are produced each year, making it the world’s most used pesticide. As a substance, glyphosate molecules bind tightly to soil. While this means they are less likely to end up in ground water as, say, motor oil, it can cause a different type of pollution. Depending on soil type and weather conditions, glyphosate can be found in the soil 6 months after being applied. Soil bacteria break down glyphosate, but I have to wonder about the chemicals those bacteria poop out afterward. Maybe it’s just me. Some studies have found that carrots and lettuce plants absorb glyphosate long after the area was treated. Compounding the problem, many glyphosate products also contain other toxic ingredients.
Glyphosate and GMOs
Glyphosate use walks hand-in-hand with genetically modified plant development. GMOs are designed to be resistant to glyphosate and other weed-killing chemicals, making it possible to grow more food for our ever-increasing global population. It certainly has its appeal. It’s so simple - just aim, squirt, and you’re done. No more weeds. But at what cost?
Glyphosate and overspray
If you (or your neighbor) use a glyphosate product, you need to be aware of the overspray risk. Since none of us is perfect, and breezes do happen, these chemicals can be carried on the wind to places where they are not welcome. That delicate, well loved exotic, handed down from your great-grandmother, is just as vulnerable to death by glyphosate as the dandelions. Also, since glyphosate products kill all the plants it touches, indiscriminately, many plants important to local biodiversity are being lost. We do not yet know the full extent of that domino effect.
Glyphosate and bees
Beekeepers have long suspected that glyphosate is, at least partly, responsible for the recent decline in global bee populations. [Did you know that China now must hand-pollinate their apple and pear trees because there are not enough bees?] New research from the University of Texas at Austin shows that glyphosate kills some of the beneficial bacteria found in a honey bee’s gut, making the bees more susceptible to infection. [Maybe we need to start feeding our bees some type of probiotic? I’m guessing.]
Glyphosate first came on the market in 1974. It provided an easy way to kill weeds with just a squirt. Glyphosate is used in agriculture and forestry, and to control aquatic plants. It is sprayed along railroad tracks, between orchard trees, and in public parks. According to the National Pesticide Information Center, there is a sodium salt form of glyphosate that is used to regulate plant growth and ripen fruit. So, it’s very useful and convenient. There are over 750 products on American shelves that contain glyphosate, including RoundUp, Bonide KleenUp Grass and Weed Killer, and Kleeraway Grass & Weed Killer. Tragically, glyphosate is also found in many oat products on grocery store shelves, according to the Environmental Working Group (EWG). The worst offenders the EWG listed include Giant Instant Oatmeal, Back to Nature Classic Granola, Quaker Dinosaur Eggs Oatmeal, and, I hate to say it, Cheerios. I urge you to read through their entire list and shop accordingly. The FDA was/is aware of glyphosate in our foods, but has failed to release its findings to the public. More recently, glyphosate has been linked to the development of Parkinson’s and Alzheimer’s diseases, and may also cause cancer in humans.
As with any herbicide, always follow the package directions EXACTLY and COMPLETELY. This is not a time to be careless. You can harm other plants with overspray, or you expose yourself to dangerous chemicals. This can occur by breathing it in during the application process, eating or smoking after applying it, if you don’t wash your hands, or by touching plants that are still wet from the spray. If exposure occurs, follow the first aid directions on the product label. For more information about risks and treatments, contact the Poison Control Center at 1-800-222-1222. Pets are also susceptible to herbicide poisoning.
Instead of using toxic chemicals to rid your garden and lawn of weeds, be industrious and put out the effort to pull them before they go to seed. While you’re out there, use it as a time to take a closer look at the other plants and the soil, and listen for the birds and insects that share your yard space.
Bottom line, glyphosate makes it possible to grow far more food, at least in the short term, but the long term costs, in my opinion, far outweigh any convenience or benefits it may provide.
Brown marmorated stink bugs have invaded the world!
Okay, so maybe that was a bit melodramatic, but the fact remains: brown marmorated stink bugs have exponentially increased their range and they can be serious garden pests.
The problem with stink bugs
Most stink bug species eat popular fruit and vegetable crops, such as apples, peas, peppers, as corn, raspberries, grapes, tomatoes, pecans, pears, peaches, nectarines, lima beans and other bean plants, blueberries, hazelnuts, and cucumbers. When they feed, stink bugs inject your garden plants with enzymes that break down plant tissue into juices they can suck up. This makes the fruit under the skin tough, and pretty unappealing to us. It also sets the stage for several bacterial, viral, and fungal diseases.
Stink bugs also feed on buds, flowers, leaves, stems, and new bark. Since stink bug populations can grow very quickly, they can cause significant damage. [They also like to overwinter in your home.] To make matters worse, insecticides do not generally work to control stink bug populations. So, what makes the brown marmorated stink bug an even bigger problem than other stink bugs?
The traveling brown marmorated stink bug
Brown marmorated stink bugs are originally from Eastern Asia. They are believed to have first appeared in the U.S., in Pennsylvania, some time between 1996 and 2001. These pests reached the West Coast in 2004, and are now found in over 40 states. While native stink bug populations tend to be controlled naturally by beneficial predators, such as parasitic wasps, this invasive pest has few natural enemies and, as stated earlier, it tends to be unfazed by chemical insecticides. This is why it is so important to be able to tell the difference between native stink bugs and brown marmorated stink bugs.
Brown marmorated stink bug identification
Adult brown marmorated stink bugs are 5/8 inch long and a mottled brown. Like other stink bugs, they have the telltale shield-shaped body. Some characteristics unique to these particular stink bugs include two white bands on the antennae, a blunt face, faint white bands on the legs, and a banded edge around the abdomen. If you are looking really closely (and why wouldn’t you?), you will also see that the thorax (shoulder area) is smooth, and there are dark bands on the tip of the membranous forewings. The folks at UC Davis made an informative video about the differences between brown marmorated stink bugs and more common, native consperse stink bugs.
Brown marmorated stink bug eggs are white to pale green, and barrel shaped. Eggs are normally laid in clusters on the underside of leaves, though I have also seen them laid in lines on bird netting. After hatching, nymphs go through fives developmental stages, or instars, in which they shed their skin, much the way a snake does, as it grows. Nymphs start out only 2.4 mm (less than 1/10 inch), and grow to reach 12 mm (just under 1/2 inch). Early nymphs are brown, with an orange abdomen. Second instars are nearly black, while later instars develop the characteristic mottled brown color. Initially, markings are red, then black, and finally white.
Managing brown marmorated stink bugs
Since insecticides don’t work, and there are few natural predators, what is a gardener to do about brown marmorated stink bugs? First, start by excluding them from your home and other buildings. Caulk openings, seal cracks, and use weatherstripping around air conditioners, doors, and windows. [This can reduce your electric bill, as well!] Next, since stink bugs are attracted to light, turn off unnecessary lights at night. [Another bonus for your utility bill.] In the case of heavy infestations, you can always use a shop vac or a handheld car vacuum to collect the little beasties. The most effective stink bug control is simply handpicking. You can drop stink bugs in a container of water with a couple of drops of dish soap, or feed the pests to your chickens.
Assassin bugs, green lacewing larvae, some parasitic wasps, and earwigs are also known to feed on stink bugs, so avoid using broad spectrum insecticides. Row covers can also be used to protect specific plants and crops against stink bug damage.
Brown marmorated stink bug lifecycle
Each autumn, these pests gather along fences, tree trunks, and buildings. From there, they move to a protected area where they overwinter in a resting stage called facultative diapause. In the spring, these adults become active again and start feeding. Within two weeks, they mate. Soon after, females begin laying the 200 to 500 eggs she will deposit in her lifetime. In the mid-Atlantic states, there are two generations each year. Here, in California, we do not yet know the extent of the brown marmorated stink bug’s reproductive capabilities. It is safe to assume that there will be even more generations here, where winters tend to be mild.
Bacterial leaf scorch is a collection of diseases that can affect a wide variety of plants.
Bacterial leaf scorch (BLS), also known as bacterial leaf spot, is a tricky disease, because it is actually several diseases caused by different strains of a single pathogen. That pathogen, Xylella fastidiosa, causes different diseases in different plants. And sometimes those bacteria strains overlap their feeding habits, making classification and control difficult.
Leaf scorch diseases
Collectively, these diseases caused by Xylella fastidiosa are known as scorch diseases. Blueberries, mulberries, pears, peppers, plums, tomatoes, and even coffee plants can become infected with bacterial leaf scorch. Scorch diseases that go by a different name include:
Oak, sweetgum, oleander, sycamore, gingko, flowering dogwood, silk trees, jacaranda, maple, and elm can also become infected.
Lifecycle of Xylella fastidiosa
This particular bacterium is what’s called a fastidious mollicute, which means it must live within a plant’s xylem to be able to reproduce. The diseases they cause occur because they get so overcrowded that they block the flow of water and nutrients through the xylem.
Not all plants are negatively affected by this bacterium. Clover, blackberry, goldenrod, and many grasses can host this pathogen, acting as a way station without suffering any consequences. Unfortunately, when a sharpshooter feeds on one of these plants and then moves to your garden, trouble can start.
Symptoms of bacterial leaf scorch
Scorch diseases are characterized by the same symptoms you would see as a result of environmental conditions, such as herbicide overspray or too much fertilizer, or other diseases, such as verticillium wilt. Initially, you will see wilting and/or chlorosis. Leaf edges look, well, they look scorched! Then leaves start dropping. Fast. Before you know what happened, the plant dies. Except when it doesn’t, because sometimes it won’t. Scientists are still trying to sort it all out.
The bacteria that cause scorch diseases are carried into your garden by leafhoppers and spittlebugs. Actually, it’s in their saliva. Sharpshooters are the biggest carriers of the disease, as far as we know. These insect pests have a wide host range of their own. As sapsuckers, every bite they take infects the plant on which they are feeding. Because their host range is so large, they are spreading diseases to plants that have never been exposed before, so they have no defenses in place.
There are no known chemical treatments for scorch diseases, so controlling the disease carriers is your best bet. If the disease appears, remove the infected plant completely and put it in the trash.
Mulching and proper irrigation can help your plants protect themselves.
Curly top may sound like a cute little redheaded kid, but it’s really a viral disease of many garden plants.
Curly top host plants
This viral disease can strike beets, beans, ground cherries, peppers, pumpkins, chickpeas, tomatoes, squash, spinach, melons, horseradish, watermelon, and more. Scientists have identified different species of virus that cause similar symptoms. For lack of better ideas, those viruses are called Beet curly top geminivirus (BCTV), Beet mild curly top virus (BMCTV), and Beet severe curly top virus (BSCTV).
Symptoms of curly top
Infected plants exhibit leaves that cup upwards or downwards, depending on the plant variety. These leaves may turn a darker green than normal, or light green to yellow, and they are thicker and more brittle than normal. Puckering and wrinkling are also common. Infected tomato leaves may have veins that look purple.
The internodes (spaces between nodes on a stem) become shortened, causing stunting and dwarfing. These symptoms are more exaggerated when infection occurs while a plant is young, and death is common. Infected older plants often just turn yellow. The telltale symptom of curly top occurs when the top of the plant turns into a rosette or tiny bouquet. If any fruit is present, the skin will be dull, rather than shiny, it will taste bad, and will tend to ripen before it reaches full size.
Curly top virus lifecycle
The virus overwinters in annual and perennial weeds. From there, beet leafhoppers (Circulifer tenellus) carry the disease to your garden plants. Symptoms don’t start to appear until long after the leafhoppers are gone, but they are the disease vector, so controlling leafhoppers goes a long way toward preventing this disease. Unfortunately, insecticides are generally not effective against leafhoppers. Leafhoppers have many natural enemies, so make your garden hospitable to beneficial insects. You can do this by avoiding broad spectrum insecticides, planting a variety of umbellifers, such as dill, carrot, and fennel, and providing a water source.
The symptoms and host plants of curly top look too much like other viral diseases, such as spotted tomato wilt, to be identified by the casual gardener. Laboratory tests are needed to know for sure. In the case of viral disease, it is simpler to yank the plant and toss it in the trash, rather than spreading the infection to other plants.
Plants may not have an active immune system, but that doesn’t mean they just roll over and take whatever hits them. When pathogens strike, plants can respond in two different ways to resist becoming infected: they use pre-existing structures and chemicals, and they can use responses that are induced by the presence of a pathogen.
Just as our skin blocks many pathogens from entry, a plant’s skin, or epidermis, does the same thing. That's why insect feeding and mechanical damage can increase the chance of a disease taking hold - the plant’s first line of defense has been breached. Plant cell walls also block viruses, bacteria, and fungi. Unlike our human immune system, which uses white blood cells to actively hunt down and destroy invaders, plant cells have antimicrobial defenses built right in. These defenses take the form of saponins, glucosides, and antimicrobial proteins. Enzyme inhibitors can also stop some pathogens from feeding on the plant. Plants also have chemicals that can neutralize toxins created by a pathogen. Finally, receptors can recognize a pathogen and alert the plant to take further action.
Inducible plant defenses
Once a pathogen is recognized, cell walls are reinforced and defensive chemicals, such as hydrogen peroxide, as well as antimicrobial enzymes and proteins, are manufactured. In some cases, plants have evolved a behavior called a ‘hypersensitive response’ in which the tissue surrounding an infection is killed off, to block further infection to neighboring cells.
Disease resistant varieties
Rather than treating a disease after it occurs, it is far easier to grow plants that have built-in defenses. This reduces the need for pesticides and fungicides. When shopping for plants, look at the plant label to see if that particular plant is resistant to diseases that tend to appear in your garden. Plant labels use the following codes to designate specific disease resistances:
So, if you see a plant label with the letters, V, F, and N, that means that particular plant is resistant against verticillium wilt, fusarium wilt, and nematodes. This does not mean the plant is guaranteed to not get these diseases, but it does mean the chances are significantly lower.
You can help your plants fight disease by selecting resistant varieties, spacing plants properly, employing crop rotation, and providing adequate water and nutrients. Also, be sure to sanitize your tools regularly, to halt the spread of disease from one plant to another.
There are no aboveground symptoms, but a carrot root fly infestation can ruin your carrot crop, along with several other umbellifers. Carrot root fly (Psila rosae), also known as the carrot rust fly, is a pest found in most temperate regions.
Carrot root fly description and lifecycle
These tiny, fast flying pests are slender, greenish-black metallic flies. Their legs and head are yellow. Carrot rust flies tend to hang out in weeds and undergrowth near carrot fields. After mating, females head for the carrots, where they will lay their tiny, white eggs on the soil surface. Larvae are creamy white, approximately 1/3 of an inch long, and rather stiff, as far as maggots go. Orangish-brown pupal cases can be found in the soil.
In addition to feeding on carrots, carrot root flies also feed on caraway, celery, dill, fennel, parsley, and parsnips. Other plants, such as lettuce, endive, and chicory can serve as host plants in areas where the maggots are already in the soil.
Damage caused by carrot root flies
Like other root maggots, carrot root maggots feed on tiny root hairs and then tunnel along the surface and burrow into the root. These tunnels and burrows are then filled with mushy frass. The initial feeding causes stunting, and tunneling makes it easy for other pathogens to enter, which leads to several different types of rot and other problems.
Carrot root fly control
The best way to protect young plants from carrot root flies is to use row covers as soon as seeds are planted, and to leave the cover in place until it is time to harvest. Some people use window screen panels around raised beds to block this pest, while others use window screen material to create protective cones for individual plants.
There are resistant varieties of carrot, specifically ‘Flyaway’, which claim to thwart these pests, though I can’t vouch for its effectiveness, personally. Research has shown that intercropping alfalfa with carrots and other host plants, or mulching with alfalfa works to reduce carrot root fly infestations. Crop rotation can also be used to interrupt the carrot root fly lifecycle.
Melon flies could end up costing California farmers over $4.5 billion if they ever get a toe-hold in the state.
Melon flies (Bactrocera cucurbitae) are a type of fruit fly. Native to India and Asia, melon flies were first seen in Hawaii in the late 1800’s. They have now become a devastating pest on the Islands. Quarantine stations have worked long and hard to prevent this pest from entering the Continental U.S. The melon fly was first seen in California in 1956, and several other times since, but whenever melon flies are identified stateside, eradication programs immediately go into affect. These programs use pheromones to attract male melon flies. These males are then sterilized and released. This messes up melon fly breeding. So far, this method has been effective. So, why would a gardener care, if the pest isn’t even here? Because maybe it is.
Melon fly host plants
It would probably be easier to list the plants that are not seen as food by melon flies, but it is important to know where to look, and to know what to watch for, so here’s the fruit fly menu of favorites from your garden:
Melon fly description
The size of a house fly, melon flies are mostly orange or yellow and brown with a pale black T-shape on the abdomen and distinct wing patterns. Wings are clear with a large brown spot at the tip and a brown stripe along the back edge and along the base. Melon fly antennae also have an especially long third segment. Melon fly larvae (maggots) are creamy white, without legs, somewhat flattened at the back end. Maggots are less than 1/2 an inch long. Pupae are somewhat smaller than the maggots, held in a protective case that can be dull white or red, or brownish yellow. Eggs are very tiny, white, and somewhat elliptical.
Melon fly lifecycle
A single female melon fly can lay 1,000 eggs. Eggs are laid on young fruit and tender new stems, which will provide food for newly hatched maggots. Eggs that have been laid under the skin of fruits, or in host plant stems, flowers, and exposed roots, will hatch and the feeding damage begins. There are three larval stages, or instars. After feeding continuously, mature maggots drop to the ground, where they burrow into the top inch of soil and enter a pupal stage. There can be 8 to 10 generations a year.
Melon fly damage
During the heat of the day, adult melon flies rest on the shady undersides of leaves. When temperatures are more comfortable, they feed on nectar, decaying fruit, sap, and bird poop. [Keep in mind, as these pests fly from one food source to another, they can be carrying pathogens from the bird poop to your fruit crop.] Tunneling and feeding create points of entry that allow bacterial, fungal, and viral diseases to enter. Generally, the fruit ends up rotten and inedible.
Melon fly control
Unfortunately, there are not any effective controls available to the home gardener. You can certainly rake up the soil under and around potential host plants, to spot, remove, and report any pupal cases you find, and be sure to quarantine new plants. Currently available insecticides have not been found to work against melon flies.
If you think you see a melon fly, please make every effort to capture or kill it. Then call the CA Pest Hotline at 1-800-491-1899, or your local Department of Agriculture, to report it. Only by working together can we protect commercial agriculture and our own gardens from the melon fruit fly. And don’t smuggle fresh fruit or produce across state lines. There’s a lot more at stake than you might think.
White mold, also known as lettuce drop, is a disease that affects far more than just lettuce in your garden.
White mold (Sclerotinia spp.) can remain dormant in the soil for a very long time. It takes a significant amount of cool moisture to wake one of these fungi up from its dormant sleep, but the underside of a head of lettuce, or a cabbage, provides just the sort of humidity needed to trigger an awakening and the ensuing infection. This disease is also known as Sclerotinia stem and crown rot and it is caused by two different fungi, depending on the host plant.
Symptoms of white mold
White mold is seen on outer leaves, lower stems, and pods, in the case of beans. Starting at the base, the mold spreads, causing outer leaves to wilt and fall away from the plant, while remaining attached. Garbanzo beans are particularly likely to become infected in the crown area. Affected plant tissue develops watery lesions as cottony white mycelium form on the surface. Mycelium are the vegetative part of a fungus, made up of threadlike hypha.
Stems may become girdled by the decay. As damaged tissue dies and dries up, it will turn white and looked bleached. Tiny (0.25–0.5 inch), irregularly shaped black flecks, called sclerotia, can be seen on the surface and inside of dead stems. Sclerotia are the resting body of the fungi, made of of a cluster of hyphal threads, and able to remain dormant for a surprisingly long time.
White mold host plants
Along with lettuce and escarole, several members of the nightshade family and the cabbage family are susceptible to white mold. This means that your tomatoes, potatoes, and eggplants, along with Brussels sprouts, mustard greens, broccoli, cauliflower, turnips, radishes, rutabagas, and kale can all become infected. Dried bean plants, alfalfa, other broad-leafed plants, and many weeds can also become infected.
How to avoid white mold in the garden
Since prolonged moisture is needed for this fungus to come among us [sorry, I couldn’t resist], keeping things dry is a good defensive plan. These specific steps can help you avoid a white mold problem in your garden:
As prevalent as white mold is, it’s a good idea to know what to look for ahead of time.
Johnson spot is a fungal disease of rice, wheat, barley, rye, and millet. It also attacks your lawn.
Other names for this disease include rice blast fungus, pitting disease, and ryegrass blast. As a threat to your lawn, Johnson spot can infect kikuyugrass, fescues, rye grasses, and St. Augustine grass.
The fungal pathogen
The fungi that causes Johnson spot is called Magnaporthe grisea (previously known as Pyriculria grisea). Magnaporthe grisea is a highly effective fungus. Spores attach themselves to plant surfaces. They can reproduce both sexually and asexually, and they are prolific. A single spore can complete its reproductive cycle in one week, though it can live for 20 days. Thousands of new spores are generated each night. I don’t know how to calculate the math on all that, but I am certain that those numbers would be overwhelming to a plant. As the fungi perform all that precreation, seed production is reduced and entire leaves are killed.
Johnson spot symptoms
Early signs of fungal infection include white to grayish green spots with dark borders. As they age, the lesions take on a more elliptical shape. These symptoms can be seen on many parts of the plant, including the leaf collar, stems (culms), and flowers (panicles).
How to prevent and control Johnson spot
Moisture is a key ingredient to this fungal growth. If leaves are wet and temperatures are between 77 and 82°F, Johnson spot can quickly take hold. To break this disease triangle, be sure to space plants in such a way that supports good air flow, avoid overhead watering, allow the soil to dry out between waterings (without causing water stress), and only apply the minimum amounts of nitrogen needed by the plants.
Of course, that advice is only partially useful when it comes to lawn care. To help your lawn avoid becoming infected with Johnson spot, water as early in the day as you can. This will allow plants to dry off before evening comes around.
This fungus has developed resistance to chemical treatments, so cultural practices are your only option. These practices include crop rotation, selecting resistant varieties, and disposing of infected plant material in the trash.
Johnson spot is the most significant disease of rice in the world. Experts estimate that this disease destroys enough rice to feed 60 million people every year.
California red scale is a citrus pest found throughout California, except in Coachella Valley, where an eradication program is in place. These insects may be tiny, but California red scale is a serious pest of citrus trees.
Like other armored scale insects, California red scale (Aonidiella aurantii) have piercing, filamentous mouthparts that are inserted into stems, fruit, and leaves, and suck life-giving sap from your tree. These particular scale insects prefer lemons, limes, Valencia and Navel oranges.
Red scale lifecycle
You will probably never see a tiny, flying male red scale. They only live for about 6 hours and have only one purpose. The females, however, attach themselves to your citrus trees, where they feed on your tree and give birth to 100 to 150 crawlers. Two or three crawlers are born every day to each female. These crawlers leave to their own feeding site. They can also be blown to nearby trees by the wind, or move from place to place by catching a ride on a bird in a practice known as phoresy - though I don’t know if they do it on purpose. Once they settle on a new location, both males and females begin to grow a waxy dome over themselves. Male covers are more elongated, while female covers are more round. Females molt two more times, while males molt under their first dome four times before taking to the air.
Damage caused by California red scale
Chlorosis, twig and branch dieback, fruit loss, and, in severe cases, tree death can all result from California red scale infestations. This damage most commonly occurs at the end of summer, when trees are water stressed and scale populations are at their peak.
How to control California red scale
Scale insects are naturally protected from pesticides. And California red scale has developed a resistance to many insecticides, so, unless you are a commercial farmer or city government, you do not have access to chemicals powerful enough to kill off California red scale. [And would you really want to spray that stuff on your food?] Keeping your trees healthy with regular, deep summer irrigation will reduce water stress. And avoiding the use of broad spectrum insecticides will allow natural predators to do their thing against scale populations. Parasitic wasps and several varieties of lady beetles can provide significant control of scale insects.
Because ants, dust, and poor air flow all make it more difficult for these beneficial predators to find and catch their prey, be sure to prune for good air flow, wrap tree trunks with sticky barriers to block ants, and give your trees an occasional rinse with the hose during the dustier parts of summer. In winter, apply dormant oils.
The next time you go water your citrus trees, take a closer look to see if California red scale has made an appearance.
Beans are easy to grow, they help improve soil structure, and they add nitrogen to the soil. They can also become infected with bean yellow mosaic.
There are three different bean mosaic diseases that occur here in California: bean common mosaic, cucumber mosaic, and bean yellow mosaic. These are all viral diseases that cause downward cupping and wrinkling of leaves, especially as leaves get older, along with the telltale mosaic pattern. Bean leaves that develop a bright yellow mosaic pattern may be infected with the bean yellow mosaic virus. There are several strains of bean yellow mosaic (BYM). In addition to beans, bean yellow mosaic can infect peas, peanuts, soybeans, black locust, and fenugreek.
Bean yellow mosaic symptoms
You can differentiate between bean yellow and the other mosaic infections because bean yellow has a yellow mosaic, rather than a light or dark green mosaic. Bean yellow mosaic also exhibits as bright yellow spots on leaves. Plants infected at an early stage of development can become severely stunted and should be removed from the garden and tossed in the trash.
Bean yellow mosaic lifecycle
The bean yellow mosaic pathogen is called, very unimaginatively, bean yellow mosaic virus, or BYMV, for short. This poorly named virus commonly overwinters in legume crops, such as fava beans, alfalfa, clovers, and vetch, as well as in certain weeds and gladiolus. The virus moves from plant to plant in aphids. When an aphid feeds on an infected plant, it becomes a carrier, transporting the disease to every plant it feeds on from that point forward.
Since resistant cultivars are not yet available, these tips may help prevent bean yellow mosaic in your garden:
Finally, if you see an infected plant, trash it.
Onions, chives, and garlic plants with pink roots are not happy.
This disease rarely causes significant problems in garlic, but it can shrink your onion and chive harvest by quite a bit.
The pink root pathogen
Pink root is caused by a fungi called Phoma terrestris. Phoma terrestris is nearly always present in the soil and it pretty much lasts forever. Normally, it causes no serious problems. If your onion plants are weakened by drought, insufficient or excessive fertilizer, water stress, insect feeding, compacted soil, or any number of other less than ideal circumstances, your onions may become susceptible. This pathogen thrives in temperatures between 75° and 85°F and can be moved around the garden by splashing rain or water, and on tools.
Symptoms of pink root
Aside from the obviously pink roots, plants infected with this fungal disease also exhibit roots that darken to red, purple, and, eventually, black. These roots shrivel up and die. These discolorations may move up into the bulb. This infection leads to stunting, but it rarely kills the plant. This disease looks a lot like fusarium wilt.
Preventing and controlling pink root
Keeping plants healthy and employing crop rotation are the two best ways to avoid pink root from causing too many problems. A note on crop rotation: do not follow a cereal crop with onions, as it creates conditions that promote this particular pathogen. Severe infestations can be eliminated with soil solarization, but that’s a pretty drastic measure for the home gardener.
If you see pink, purple, or black shriveled roots on your onions, try growing them in a different area, in fresh soil, and be sure to feed, weed, and water them properly, and protect them from insects, to ensure that they stay healthy enough to protect themselves.
If the lower limbs on your almond tree are turning brown, you have a problem.
While it is normal for the leaves on lower limbs to turn yellow because of being shaded by the limbs and leaves above, lower limb dieback (LLDB) goes much farther and can result in the death of your tree. LLDB first appeared in 2005. Scientists do not yet know what causes this condition, but learning how to avoid it can save your trees.
Symptoms of lower limb dieback
This disease normally appears in late April or May, on trees that are 7 or 8 years old. It starts out with the leaves on lower limbs yellowing, and then turning brown. Eventually, the entire branch becomes girdled by cankers and dies, right up to where it attaches to larger, scaffold branches, or the trunk. If you scrape the bark off of an affected limb, you will see brown spots in the wood. [Sorry, but I couldn't find an image I could use.]
Some almond varieties are more susceptible to lower limb dieback than others. Padre almonds are the most likely to get this disease, with Butte being a close second. Almond varieties that show some resistance to lower limb dieback include Aldrich, Carmel, Fritz, Mission, NePlus Ultra, Nonpareil, Sonora, and Wood Colony. If you are shopping for an almond bare root tree, you might consider one of these more resilient varieties.
Preventing lower limb dieback
While research is currently underway, it is believed that overly wet soil, low light levels, and root exposure to herbicides or excessive fertilizer may weaken trees, making them vulnerable to whatever it is that causes this problem. This is just the opposite of shade tree decline, in which severe drought slowly kills a mature tree, with the early symptoms being a lack of leaf cover in the upper canopy, or crown, of the tree.
Lower limb dieback occurs most often in years with a cool, wet spring, followed by high temperatures. Soil compaction and low infiltration rates are also believed to play a role in lower leaf dieback. Trees with hull rot also appear to be more likely to develop this condition. In this case, fumaric acid and other toxins are believed to accumulate in larger branches when multiple spurs are infected. In this weakened state, these trees are also more likely to be infected by fungal opportunists, such as Botryosphaeria dothidea and Phomopsis amygdali. Phomopsis amygdali causes the stoma to stay open, desiccating the tree. Botryosphaeria dothidea causes cankers on a wide variety of plants.
Keeping your trees healthy is the best way to prevent lower limb dieback. This means proper irrigation, reasonable applications of fertilizer (only after a soil test shows a need for it), and control of scale insects, which may play a role in the spread of this disease. Fixed copper, sulfur, and fungicide treatments have not been shown to be effective.
If you love your trees (or your blueberries), be on the lookout for Asian longhorned beetles.
Native to China, Japan, and Korea, these invasive, wood boring beetles love to hitch overseas rides on wood-related packing materials: shavings, pallets, that sort of thing. In 1996, an infestation of Asian longhorned beetles (Anoplophora glabripennis) was discovered in Brooklyn. Two years later, a second sighting occurred in Chicago. Then, they were found in New York, New Jersey, and Illinois, where they are responsible for the removal of thousands of trees. These pests have already cost state and federal government (our tax dollars) over $168 million and that number looks to rise exponentially, now that they have expanded their range into California and Washington.
The potential economic impact was first estimated to be more than $41 billion. That number has increased to nearly $700 billion, and that’s before you factor in the damage to breakfast morale when the northeast’s sugar maples are attacked! Eradication efforts got into affect each time these invasive pests are found, sometimes successfully, sometimes not. The U.S. Customs Department is working hard to halt the importation of these pests. Eradication in the U.S. is still possible, but it’s an uphill battle. And they need our help.
Asian longhorned beetle identification
Asian longhorned beetles (ALBs), also known as starry sky or sky beetles, are easy to identify. Approximately one inch wide and and an inch-and-a-half long, they are shiny black with 20 white spots on each wing cover, and they feature an impressive set of black and white banded antennae. They have long, whitish-blue feet and large mandibles. Larvae are large and cream colored.
Adult female beetles chew pits into wood and then deposit their eggs into those pits, one at a time. She can lay up to 90 eggs in just a few weeks.
When the eggs hatch, larvae tunnel deep into the tree (where they are safe from predators and pesticides), leaving behind a trail of frass. Deep within the tree, the larvae go through several instars before entering a pupal stage.
As adults, they tunnel out of the tree, leaving 3/8-inch exit holes along trunks and branches. Piles of frass can be seen at the base of infected trees and in branch crotches. Branch dieback and leaf wilting are early signs of infestation. The egg sites and larval feeding make the trees susceptible to many other pests and diseases, as well as more vulnerable to damage from heavy winds. Sap is often seen oozing from wounds. This larval tunneling causes extensive damage and girdling, making the wood unusable and eventually killing the tree. Infested trees must be removed and destroyed by trained professionals. Do not attempt this yourself.
Trees susceptible to ALB
Many popular hardwood trees are vulnerable to ALB infestation. These trees include alder, ash, beech, birch, boxelder, elm, hackberry, hornbeam, horse chestnut, mimosa, planes, poplar, sycamore, and willow. And blueberries! And members of the Prunus family, which includes apricots, peaches, nectarines, cherries, and almonds! We do not yet know what the impact will be on California’s native hardwood trees.
Experts predict that this pest could cause more damage than gypsy moths, Dutch elm disease, and chestnut blight combined, destroyed millions of acres of trees across the country, in parks, along streets, in backyards, and in agriculture. Dead and dying trees are more likely to cause fires and they are unable to support the biodiversity that keeps a region healthy. If you consider all the wood-based products we use every day, ALB could cause many prices to increase significantly. All because of an insect.
If you see it, catch it! Report it!
If you see an Asian longhorned beetle, catch it. Period. Just do it. They don't bite or sting. While they can fly, they don’t do it very well and only for short distances. You can do this.
Your efforts could save millions of trees and billions of dollars. Seriously.
Put your captive in a glass jar [they chew through trees, remember?] and place it in the freezer. Be sure to label the jar with where you found it (GPS position, if possible), the date you found it, and your contact information. These reports are critical if we are to protect our trees. Using this information, experts can create quarantine zones and implement eradication programs most effectively.
If you live in California, call the CDFA hotline at 1-800-491-1899. In fact, put the number in your phone now, so you’ll have it if you ever need it. I did. If you live outside of California, report it to your state’s Department of Agriculture. Together, we can save millions of trees.
Pierce’s disease is becoming a major threat to grape vines.
The bacteria responsible for Pierce’s disease, Xylella fastidiosa, was first seen on grapes in Southern California in the late 1800’s, when it was called Anaheim vine disease. By the 1930’s and 1940’s, it had spread to California’s Central Valley. By the late 1990’s, the disease had spread to several California counties. This increase is believed to be, in part, a result of warmer temperatures allowing more of the bacteria to survive the winter. According to CABI, Pierce’s disease is now found throughout the Americas, and in Italy, Iran, and Taiwan.
Pierce’s disease is carried by sap-feeding insects. Most commonly, this means sharpshooters, such as blue-green and glassy-winged sharpshooters. [Did you know that sharpshooters can consume hundreds, or even thousands, of times their body weight in sap in their short lives?] Spittlebugs have also been found to carry this disease. Whichever insect is chewing on your grape vines, they inject the bacteria into the vine’s vascular bundle as they feed, making them a disease vector. These bacterium then live and reproduce in the xylem, clogging the flow of nutrients and water through the plant.
Pierce’s disease can occur on a large number of weedy and ornamental crops, such as wild grape, California blackberry, periwinkle, stinging nettle, eucalyptus, live oaks, blue elderberry, and mugwort. These plants are not affected by the bacteria that cause disease in grapes. But they do provide a transitionary location for the insects that carry the disease to your garden.
Symptoms of Pierce’s disease
Infected plants exhibit leaf scorching and stunting. These symptoms start out as slightly yellow or red leaf margins (edges) of white or red grape varieties, respectively. Concentric areas of infected leaves may dry up. You may also see ‘matchstick’ petioles, ‘green islands’ on mature brown stems, raisined clusters of fruit, and dieback. These symptoms do not normally appear until spring, after temperatures are above 65°F.
There is no cure for Pierce’s disease. In some cases, the disease will disappear on its own and we don’t yet know how or why. It seems to be a function of temperature, the timing of the initial infection, and the variety of plant being infected. Generally speaking, a late season infection, one that occurs after June 1st, has a 95% chance of recovery. Water stressed plants are more likely to succumb to the infection. If a plant becomes infected early in the season, the bacteria have time to become firmly established. Once that happens, you will ultimately have to remove the vine completely.
Pierce’s disease control and prevention
This disease triangle consists of the host plant, the feeding insect carrier, and the disease-causing bacteria. Break the connection between any one of those three and you can reduce the chances of disease. The easiest ways to prevent Pierce’s disease is to keep host weeds out of the area and treat for the sap-sucking insect pests. Since insect-eating birds, such as bluebirds, along with several predatory insects, love to eat sharpshooters, keep your garden welcoming to these natural helpers.
Monitor your plants for signs of Pierce’s disease so that you can act quickly, reducing the spread of the disease. Most of the vector insects are low fliers, so physical barriers can be used to quarantine potentially infected plants. During the dormant season, remove any vines that have been infected for more than one year. They will not recover and they will spread the disease to other plants as vector insects feed on them and then move to nearby plants for more feeding.
Moles are creatures of darkness. They almost never leave their tunnels. Often falsely blamed for plant damage, moles are primarily insect eaters.
Differences between moles and pocket gophers
Many people assume that moles and voles (also known as pocket gophers) are related. They are not. Voles are plant eating rodents, while moles are primarily insect-eating members of the Scapanus species, more closely related to shrews. Crescent-shaped mounds with closed holes indicate the presence of pocket gophers. Pocket gopher populations can lead to girdled trees, slope erosion, and dead plants. Moles, on the other hand, have round mounds which may have open or closed holes, and long surface ridges from their shallow tunnels are often visible. Moles normally feed on worms, grubs, insects, and other invertebrates. Moles will occasionally eat mice, shrews, and nuts. Your average mole will eat 40 pounds of insects each year.
Moles are rather funny looking. They have stubby, hairless tails, cylindrical bodies (usually 5 to 7 inches long), pointed snouts, and short, webbed hands and feet. They don’t see very well because their eyes are covered with skin, and you can’t see their ears. Mole fur, however, is quite thick and velvety, and moleskin is the stuff of hiking blister legends. There are 42 mole species worldwide, 7 of which live in North America, and 4 species found in California:
Moles like their privacy. Unless it’s the breeding season, you will only find one mole per tunnel system. Moles have one litter each year, usually with 3 or 4 young, in spring.
Moles create an extensive system of both deep and shallow tunnels. The deeper tunnels are their permanent housing, with separate rooms for food storage, sleeping, and rearing young. Tunnels are usually 2 inches in diameter and found 8 to 12 inches below the soil surface. The shallow tunnels are for hunting out grubs, worms, centipedes, and other soil dwelling creatures. It is the shallow tunnels that cause most of the problems associated with moles. As they burrow under the surface of the soil, looking for their supper, moles often dislodge smaller plants and expose root systems to the air, drying them out. If you want a lawn that looks like a putting green, moles are not your friends.
If you cannot tolerate moles in your garden or landscape, trapping will be necessary. While there are dozens of repellants, scaring devices, home remedies, and plants that claim to offend moles, research has not shown that any of these methods actually work. The only exception is castor oil solutions, which have been shown effective on eastern moles. Flooding tunnels wastes water and does not rid an area of moles. [They’ve dealt with floods for far longer than we have been gardening.]
Trapping always works. Underground harpoon traps and scissor-jaw traps are the most effective methods. Of course, this means dealing with a dead mole and a messy trap. Some new mole baits are showing limited effectiveness, but then you have to worry about children, pets, and local wildlife also suffering a horrible death. Plus, if your landscape was appealing to a mole before, it probably will be again, to a different mole. If you have valuable plants that need protection against moles, you can install a hardware cloth barrier 2-feet into the ground, with a 6-inch lip bent at a 90° angle away from the plant to thwart mole digging.
Moles are fascinating creatures. Some of the more interesting mole facts include:
If you can tolerate moles, they actually provide many benefits to the garden and landscape.
Did you know that mole saliva contains toxins that paralyze earthworms? Researchers have found underground storage spaces filled with thousands of paralyzed earthworms, for later eating.
Now you know.
Kuno scale is a pest of plum and other stone fruits.
Like other soft scale, kuno scale (Eulecanium kunoensis) is a sap-sucking insect that hides under a dome-shaped protective barrier. Unlike armored scales, which can be separated from their dome, kuno and other soft scales are attached to their dome.
Kuno scale lifecycle
Eggs hatch under their mother in spring. These first instar nymphs are called ‘crawlers’ because they crawl away from her and find a place to feed on leaves throughout the summer, going through multiple instars as they feed. In fall, mature nymphs find a hiding place on twigs just before leaf fall. These nymphs overwinter on twigs and reach adulthood in spring, just in time to lay more eggs.
Kuno scale damage
As a sap-sucking insect, Kuno scale sucks phloem sap from twigs and leaves. While it prefers plum trees, Kuno scale can also be found on peach, cherry, nectarine, apricot, and almond, as well as rose, walnut, and pyracantha. These pests can populate an area so quickly, that it can seem as though they appeared overnight. Plants may appear water stressed. Heavy infestations can lead to twig dieback and premature leaf drop. Also, Kuno scale produces a lot of honeydew (sugary poop). Honeydew is the perfect growth medium for sooty mold. It also attracts ants, which will protect and farm Kuno scale. If you see ant trails on your plum tree, make a point of finding out where they are going in your tree.
Kuno scale control
Since ants protect Kuno scale from natural predators, blocking ants from getting up in your trees is the easiest control measure. To do this, simply wrap the tree trunk with a sticky barrier. You can also apply horticultural oil to twigs and the ends of branches just as buds are swelling, in spring. You can also try drenching the undersides of leaves in early summer, but this is tricky, because it’s not a good idea to spray dormant plum or walnut trees with oil, especially during periods of drought.
And, let’s face it, spraying the underside of leaves is a royal pain.
What happened? Yesterday, your plants looked lovely. Today, several leaves are rolled up, looking like green cigars. What did this, is it a problem, and what can you do?
Physiological causes of leafroll
Leafroll (or leaf roll) can indicate environmental problems, such as water stress, too much nitrogen, drought, excessive heat, root damage, severe pruning, overspray, or transplant shock. Moderate upward cupping is usually first seen in lower leaves, spreading inward and upward, as the cupping progresses into a full blown leafroll. Leaves affected by these physiological conditions will thicken and become leathery as the plant tries to protect itself. This response is common to members of the nightshade family. Luckily, it has very little impact on fruit production or quality of tomato, eggplant, or pepper plants.
Leafroll is also a family of viral diseases that can infect many different plant species. These viruses enter plant tissue as their insect carriers feed. These carriers are normally aphids, mealybugs, and soft scale insects. The leafroll virus can also be spread through infected scion wood. Once infected, vascular bundles become clogged as the viruses reproduce in the nutrient-rich phloem. This reduces water and nutrient flow within the plant, causing stunting, delayed maturity, reduced crop size, chlorosis, necrosis, leaf curling, and leafroll.
There are three major types of leafroll that warrant concern:
Because these viruses can spread rapidly, over relatively great distances, close monitoring and control are in everyone’s best interest. Once a plant is infected with one of the leafroll viruses, it should be removed and destroyed. There is no cure or treatment. When shopping for plants, choose resistant varieties, and be sure to control carrier pests, to reduce the likelihood of leafroll affecting your garden.
You can grow a surprising amount of food in your own yard. Ask me how!