Since people first started growing plants for food, we have been battling the pests that eat, damage, or infect those plants.
Initially, those battles were hand-to-hand combat. Pests were removed by hand, chased away, and puzzled over. Then came the age of ‘better living through chemistry’, when powerful concoctions were sprayed willy-nilly, threatening entire species. Now, the pendulum has swung in a new, more balanced direction. That direction is called integrated pest management.
Integrated pest management (IPM) is a program of science-based pest controls with the minimal disruption of natural cycles and least harm to other organisms. Integrated pest management was made a national policy in the U.S. by President Nixon in 1972.
What are pests?
Your younger brother or sister may have been a pest when you were kids, but garden pests never outgrow the potential to cause damage. Garden pests include any organism that can harm or hinder the plants we want to grow. Using this definition, a pest can be disease-carrying bacteria, viruses, or fungi, a plant-eating insect or animal, a competitive weed, destructive soil nematodes, or a neighbor’s cat that thinks your carrot patch is its litter box.
What is IPM?
IPM takes a long view on reducing the negative impact of pests in ways that are sustainable and responsible. An integrated pest management plan has six basic tenets:
Rather than relying on a single method of control, IPM combines these tenets, in the order presented, to reduce the negative impacts associated with killing off pretty much anything. Rather than spraying chemical pesticides and insecticides on your food plants and into the soil and water table, you can work your way through these sustainable practices for surprisingly effective control of most garden pests.
Monitoring for pests
The first step in an IPM program is monitoring. Monitoring involves more than simply looking for bugs. Monitoring for problems begins by arming yourself with factual information about your soil and microclimate. This means sending out a sample for a soil test. Test results will let you know which nutrients are at acceptable, toxic, of deficient levels, along with soil pH, soil organic matter levels, and base saturations. It also means noting sun and wind exposure levels at various locations in your yard, the likelihood of frost damage, drainage problems, and preexisting pest problems. Each of these conditions play powerful roles in keeping plants healthy enough to defend themselves against pests.
After collecting all that information, go outside and start look for pests. You don’t know what you are up against without looking. You can use pheromone traps and yellow sticky sheets to help collect information of what costs are present. As you see pests, learn to identify them and then read up on them. Learn enough about them to counteract the damage they do without causing undo damage of your own. This is where things like trap crops come in handy.
The next step is to decide just how much damage you are comfortable with. Wiping out entire species is generally not a good plan. Evolution takes time and the balances that are created can be delicate and easily thrown out of whack. Allowing tolerable levels of pests to be present provides food for beneficial insects which will help you fight the battle against those and others pests.
Cultural practices are the way you manage your garden. Do you use overhead watering, which can encourage fungal disease, or do you use soaker hoses? Pruning for proper air flow and good structure go a long way toward pest control. There are several good cultural practices that help your plants stay healthy:
The third plan of action is mechanical controls. Row covers, tree cages, tomato cages, netting, sticky barriers, brassica collars, mulch, shade cloth, tree supports, trellising, and fencing are common mechanical controls that help plants stay healthy. This stage of pest control also includes trapping, hand picking, and soil solarization. Cold frames, greenhouses, and hoophouses also provide mechanical controls that reduce pest damage by making life harder for the pests.
There is an army of beneficial insects ready to help you control pests naturally, if you will only get out of their way. Instead of using chemical pesticides and insecticides, which can kill off beneficial predators and parasites, install insectary plants and provide water to create a welcome habitat for the natural enemies of the pests in your landscape.
Other biological controls include the release of sterile insects (generally performed by government agencies and universities) and introducing other natural predators periodically. Unfortunately, buying ladybugs and other predators rarely works as well as you might hope. They generally don’t stick around. Creating a welcoming environment is far more effective.
Chemical pesticides are used as a last resort. Pesticides should be selected as appropriate for the specific pest being controlled and used in ways to avoid affecting non target organisms.
Whichever chemical controls you use, it is important to switch things up periodically to prevent the likelihood of pest resistance. Pest resistance occurs when an organism develops an immunity toward a treatment, making it necessary to use ever-stronger poisons against them. Insects and pathogens evolve much faster than we do, so there is a limit to what we can tolerate.
Finally, after monitoring the situation and deciding which pests can be tolerated, using good cultural, mechanical, biological controls, and applying only necessary chemical controls, be sure to assess the situation, to make sure the problem is being corrected. If it isn’t, you need to go back and learn more about the pest(s) causing the problem to develop a new plan of action.
Generally speaking, pests appear seasonally and on specific crops. Knowing when to look and where to look can give you a jump-start on controlling the pests that damage your garden plants.
You can help the scientific community by participating in citizen science projects, such s the Big Bug Hunt, where you report insect sightings as you see them. This helps researchers develop better predictions about when pests are likely to appear in your area.
Western grape rootworms are leaf beetles that eat the leaves of grapes, roses, and fireweed in spring and summer. If that weren’t bad enough, their offspring are found underground, chewing up the root system. The combined effect can be devastating.
Western grape rootworm description
These beetles are very small, averaging only 1/7” in length. This works out to 4 or 5 beetles standing end-to-end across a dime.
Unlike their more tan-colored cousins, western grape rootworms are usually black or reddish-brown with dull gray, yellow, or white hairs, and orangish-red antennae. Larvae are 1/4-inch long, C-shaped white grubs. These grubs have 3 pairs of prolegs, a reddish brown head, and black or brown mouthparts. Eggs are laid in clusters on old wood under loose bark.
Male western grape rootworm beetles rub their legs together to attract females, the same way crickets and grasshoppers do each summer.
Damage caused by western grape rootworms
These beetles cut slit-like holes in leaves, shredding them to tatters. The leaves then dry up and die, reducing photosynthesis and food for the plant. Adult beetles may also be found feeding on berries, petioles, and the bark of new shoots. Underground, western grape rootworm larvae feed extensively on the root system and can cause considerable damage.
Controlling western grape rootworms
Since larvae spend most of their year 2-feet underground, control is generally only possible during spring, when larvae and adult beetles move to the surface. Monitor plants for signs of beetle feeding and handpick whenever possible. You can also use sticky barriers to capture beetles moving up and down the trunk.
If you see a tiny beetle playing ‘possum, don’t be fooled. The western grape rootworm beetle uses that trick to avoid being eaten, often falling off a leaf, stiff-legged.
With a name like Asian jumping worms, you might expect colorful, flamboyant gymnastics moving gleefully through the soil, helping your plants grow.
Okay, that was a stretch. And you’d be mostly wrong.
I say mostly because, while not colorful, these worms really can move. Also known as snake worms, crazy worms, and Alabama jumpers, Asian jumping worms writhe violently when disturbed. They can even drop their tail when threatened.
Sadly, instead of helping plants grow, these voracious feeders strip an area of nutrients, destroying the top soil layer, and leaving desolation in their wake. This interrupts thousands of years of evolution and nutrient cycling, threatens biodiversity, and increases erosion.
The invasives mixed bag
Before we get into the Asian jumping worm story, let me remind you that our beloved European nightcrawlers and honey bees are also non-native species. Sometimes invasives can be a good thing. This is not one of those times.
As with many other situations involving invasive anything, the problem lies in imbalances. North American forests and farmlands have evolved, over thousands of years, to use surface plant litter as slow-release food and secure habitat for countless microorganisms, insects, reptiles, amphibians, and other life forms. Asian jumping worms eliminate that layer and they do it very quickly.
What are jumping worms?
Our more sedate earthworms tend to be reddish brown with a raised white or grey partial band part way down the body. That band is called the clitellum. Asian jumping worms, which can range from 3 to 7” long, are grey to dark brown, with a smooth the clitellum that goes all the way around and is closer to the head end.
Also, while shiny, jumping worms do not produce the slime seen on many earthworms. Regardless of how you feel about that slime, it is very useful in creating soil aggregates that allow for the healthy movement of air, water, microorganisms, and roots through the soil. Jumping worms also tend to be more rigid than our squishy earthworms.
There are three species of Asian jumping worm: Amynthas agrestis, A. tokioensis and Metaphire hilgendorfi, with A. agrestis being the most commonly seen. Native to Southeast Asia, jumping worms are believed to have been brought to North America in potted plants, bagged soil, or nursery stock, though we don’t know exactly when or how.
Asian jumping worms have moved quickly westward, in worm terms, over the past 10 years and are now found in Oregon. As you can imagine, these continued movements are not just worms traveling on their own. Asian jumping worms end up in plants, mulch, and soil, on shoes and equipment, in agricultural produce, and in batches of fishing bait. They get transported by us, one gets loose, the problem spreads. It’s easy to do because these jumping worms spend their winters as tiny, pinhead size cocoons, filled with eggs, they reach adulthood twice as fast as our familiar earthworms and red wigglers, reproduce more rapidly, and are more aggressive. They can also thrive in higher densities and eat a wider variety of foods.
The real problem with Asian jumping worms is where and how fast they feed.
Damage caused by Asian jumping worms
Asian jumping worms are too efficient. That may sound like a good thing, but too much of a good thing can be a bad thing. Let me explain.
As earthworms feed on fungi and bacteria that grow on decomposing organic material, they burrow into the soil, excreting castings that are filled with broken down plant and animal material, churning the soil and improving soil structure, soil health, water retention, drainage, and nutrient cycling. Everybody’s happy. Plants and organisms grow. Life goes on.
Asian jumping worms are eating machines, quickly devouring all of the surface material in an area and leaving behind a trail of low-nutrient crumbles prone to serious erosion. Research has shown that jumping worm castes are different from those of other worms. Instead of the soft, brown, crumbly bits of plant food and soil amendment we associate with earthworm castings, Asian jumping worm castings look more like a pile of coffee grounds.
Asian jumping worms process nutrients so rapidly that their feeding releases nutrients faster than plants can absorb them, causing the nutrients to be washed, blown, or leached away. These castings contain important plant nutrients, such as potassium and calcium, and they tend to contain higher levels of heavy metals, such as iron and aluminum. When those crumbles are eroded away, those nutrients are lost. As a result, Asian jumping worm feeding quickly converts healthy, loamy soil in to granular, more sandy soil that tends to be hydrophobic, which means water runs off instead of sticking around long enough for plants to absorb. These invasive worms also push nutrients so deeply into the soil subsurface that many shallow-rooted plants cannot reach those important nutrients, leaving them to starve.
What can you do about jumping worms?
In a word, be diligent. Asian jumping worms generally cannot survive freezing winters, but anything less than that and they can become a serious problem in your yard. You can help prevent the spread of these invasive worms with these handy tips:
Bottom line, earthworms create topsoil while Asian jumping worms destroy it. Of course, that’s an oversimplification, but I want you to understand how important it is that these pests are kept in check.
If you suspect the presences of Asian jumping worms in your garden, conduct a mustard test using these steps:
Basil’s fragrant leaves make it a garden favorite, but there is a new disease on the horizon: basil downy mildew. And warm, moist conditions are all basil downy mildew needs to set up housekeeping on your basil plants.
First seen in Africa, in the 1930’s, basil downy mildew (Peronospora belbahrii) came to the U.S. in 2004 on infected seeds from Italy. By 2008, it had made its way to California and is now a global problem for everyone who enjoys basil and pesto.
Like other downy mildews, basil downy mildew is caused by tiny, algae-like microbes called oomycetes. Oomycetes parasitize vascular plants to complete their life cycle. They do this by collecting on the underside of leaves. From there, these tiny one-celled creatures send out threads that enter the leaf through the stoma and begin propagating. Since the oomycetes cannot pass beyond leaf veins, the damage from each infection is usually contained between leaf veins.
New spores are then released through the stoma, where they fall to soil, waiting to be splashed right back up by rain or irrigation water, or caught on the breeze for a ride to a new host plant. The party responsible for basil downy mildew travels on a variety of surfaces to reach your garden. In addition to water and wind, spores can be carried on garden tools, clothing, transplants, and infected seeds.
So how do you know if your basil plants are infected?
Symptoms of basil downy mildew
Unfortunately, the earliest sign of infection, yellowing leaves, looks a lot like nutritional deficiencies. If you see yellowing between the major leaf veins with dark blotchy areas, take a closer look on the underside of those leaves. If you see purple or gray powdery spores, it is probably basil downy mildew. Those spores are reproductive bodies and each infected leaf is a disease factory.
Once a plant is infected, it is too late. Harvest any healthy leaves and bury the plant under soil or in the compost pile to prevent spores from spreading. Generally speaking, these pathogens will not survive in compost or through winter temperatures. We hope. For now, the basil downy mildew pathogen is under California State quarantine, which means infected plants must be destroyed.
Preventing basil downy mildew
To avoid being part of the problem, be sure to buy only certified disease-free seeds and seedlings, place all new plants in quarantine, and monitor plants closely.
Good air circulation goes a long way toward keeping leaves dry. Dry leaves are not hospitable to this disease, so keep irrigation water at ground level. Skip the watering can. Instead, use a soaker hose or drip system that will prevent spores from splashing up onto the underside of leaves.
At the end of the growing season, cut basil plants off at ground level and compost them completely. Do not leave them in place to harbor disease. This helps break the disease triangle and reduces the chance of things starting up again each spring.
Some research is being done on the effectiveness of spraying basil plants with fixed copper as a preventative, but the results are not yet in.
If you think basil downy mildew has appeared in your garden, please notify your local County Extension Office or Department of Agriculture. You can even use the Basil Downy Mildew Reporting Page to add you contribution to science!
What do peaches and potatoes have in common? The green peach aphid.
Considered the world’s worst disease vector among garden plants, green peach aphids (Myzus persicae) love to feed on peach and potato leaves, along with dozens of other garden plants.
Green peach aphid description
Green peach aphids are generally found in colonies of winged and wingless adults and immature nymphs. Green potato aphids look a lot like potato aphids (Macrosiphum euphorbiae). While potato aphids can be seen throughout the plant, green peach aphids prefer hiding on the underside of leaves.
Damage caused by green peach aphids
Green peach aphids often overwinter in the egg stage on stone fruits, particularly on peach and peach hybrids, though apricot and plum are also favored. In spring, these eggs hatch and nymphs begin feeding on buds, flowers, and new stems. A few generations later, which only takes a month or so, winged adults move to summer feeding areas. It would probably be simpler to list the garden plants that do not attract green peach aphids, but you do need to know where to look for these pests.
Summer feeding can occur on artichoke, asparagus, beans, beets, broccoli, Brussels sprouts, cabbage, carrot, cauliflower, cantaloupe, celery, chili peppers, corn, cucumber, fennel, kale, kohlrabi, turnip, eggplant, lettuce, mustard, okra, parsley, parsnip, peas, peppers, potato, pumpkin, radish, spinach, squash, sunflowers, tomatoes, turnips, watercress, and watermelon.
Aphids prefer feeding on tender new growth. This leads to wilting, water-stress, and stunting. It also generates a lot of honeydew (sugary insect poop), which provides the perfect growth medium for sooty mold. Heavy aphid feeding can weaken a plant to the point of death. The bigger problem, as with nearly all aphid species, is that these pests carry diseases. Green peach aphids may infect plants with a variety of viral diseases, including:
If potato leafroll virus appears in your garden, it is a good idea to remove the infected plant, plus three other plants in every direction, to prevent green peach aphids from spreading the disease even further. This is yet another reason why it is so important to plant certified disease-free plants in the first place. These pests are often found in greenhouses, so placing new plants in quarantine can go a long way toward preventing an infestation. They can also travel on the wind, so it's a constant battle.
Green peach aphid management
The best way to control green peach aphids is to hit them in winter. This means removing overwintering sites, such as infested leaves, spent plant debris, and nearby weeds. Malva is a popular winter wonderland for aphids, so keep that weed away from your peach trees and potato plants. Bindweed, lambsquarters, penny cress, pigweed, sowthistle, tumbleweeds, white goosefoot, and rouge members of the nightshade family can also provide overwintering sites for this pest.
As spring and summer come around, however, you can attract and protect beneficial predators, such as lady bugs, lacewings, parasitic wasps, and syrphid flies, by providing fresh water, planting a variety of insectary plants, and avoiding the use of broad spectrum pesticides. Most chemicals designed to kill aphids cause more harm than help by disrupting the lifecycle of many natural predators. There is also a parasitic fungus (Entomophthora aphidis) that attacks aphids, but you can’t do anything about that one.
Early each June, in northern California, green peach aphids migrate into our gardens. You can prevent a full-blown infestation by monitoring plants on a weekly basis and using a damp rag or paper towel to wipe off colonies before they can really start propagating. A single female, hatched in spring, can reach sexual maturity in only 10 days, creating 20 generations in a single year. By the end of summer, this can result in billions of offspring.
Armillaria root rot is a soil borne that attacks the roots and trunks of many fruit and nut trees. It is also the largest living fungi in the world.
In Oregon’s Malheur National Forest, there is a mushroom colony that covers 2.200 acres. That colony is believed to be a single entity, all growing from the same network of fungal mycelium.
By itself, that's impressive. In your tree, it's a deadly fungal disease.
Trees vulnerable to Armillaria root rot
Also known as honey fungus, shoestring fungus, or oak root fungus, Armillaria root rot (Armillaria mellea) is a deadly disease that infects avocado, cherimoya, cherry, chestnuts, conifers, kiwifruit, kumquat, lemons and other citrus, pomegranate, stone pine, and walnuts, along with the mighty oak. If that weren’t bad enough, trees weakened by Armillaria root rot become more susceptible to serious pests, such as Pacific flathead borers.
Armillaria root rot symptoms
Everything starts out looking fine. Your tree is growing nicely and you suspect nothing. Suddenly, you notice downward cupping leaves, chlorosis (yellowing), dieback of upper limbs, and leaf drop. You may also see a variety of mushrooms growing nearby.
Your tree is dying. Young trees die quickly, while older trees make take longer, but the end result is nearly always the same.
Armillaria root rot diagnosis
If your tree shows the above mentioned symptoms, take a closer look at the base of your tree. You may be able to see fan-shaped fungal growth rising up the trunk from the soil level. Use a sharp knife and cut away a section of bark at the base of the tree, so you can see the cambium layer. If you see white fungal threads (mycelia) and can smell a strong mushroom odor, your tree is in serious trouble. If you see reddish brown streaks or patches, or water-soaked areas, the infection is more likely to be Phytophthora root and crown rot, rather than Armillaria, though that isn't any better news for your tree.
If you have easy access to the tree’s roots, cut one open. Infected roots are darker than normal and have a cottony center. You may also see black rhizomorphs, called ‘shoestrings’, on the surface of infected roots.
How Armillaria spreads
As a soil borne disease, Armillaria mycelia can remain viable in the soil for many years. It isn’t until a healthy root comes into contact with infected wood, roots, stumps, or other wood fragments. Then, the fungus enters the healthy tree and begins to populate the cambium layer, eventually killing the tree. Infected nursery stock can also carry this disease, so always quarantine new plants.
Preventing Armillaria root rot
Good drainage, sunburn protection, and proper (not excessive) irrigation can all help protect your trees against Armillaria root rot. Once infection occurs, the tree should be completely removed and the area should only be planted with crops that are not vulnerable to Alternaria root rot.
Dark brown spots on your tomatoes? It’s probably early blight.
Cool spring temperatures and too much rain or other moisture creates the perfect storm for this fungal disease. The early blight fungus (Alternaria solani) is a disease of the nightshade family, which means your potatoes, eggplants, bell peppers, and chili peppers are equally susceptible, as are other plants in the nightshade family, such as petunias and blue potato bushes. If similar lesions are seen later in the season, it is more likely to be late blight, also known as the dreaded potato blight.
Early blight was once a disease found only on the east side of the Rocky Mountains. Sadly, that is no longer the case. The early blight pathogen is now found everywhere host plants have been grown and can result in up to 30% of your potatoes and 79% of your tomato crop ending up in the trash bin.
Early blight symptoms
Small black or brown spots, usually 1/4 to 1/2 inch in diameter, may appear on fruit, leaves, and stems. These spots may have a concentric rings pattern, or bullseye. Fruit spots are dry, sunken areas, most commonly seen near the calyx end of the fruit. [That’s the flower end, as opposed to the stem end.] Spots on leaves feel leathery. Symptoms are seen on older leaves first. Stem lesions do not have the same circular, bullseye pattern.
In some cases, this pathogen can cause collar rot and damping off, which usually kills seedlings. As the disease progresses, leaf loss can significantly reduce fruit production. Honestly, the fruit that is produced doesn’t look particularly appetizing. Infected potatoes either rot in the ground or in storage.
Early blight lifecycle
Fungal spores overwinter in the soil and on infected fruit and plant debris. Rain and overhead irrigation splash spores onto plants, where they begin reproducing. To reduce the chance of early blight in your garden:
Fixed copper or sulfur sprays can provide fungicidal benefits in heavy infestations. Also, healthy plants are less likely to become infected, so feed and water your plants properly, give them enough space to reach full size, and help them avoid physical injuries, which provide entry points for early blight fungal spores.
Two-spotted spider mites can kill off many of your garden plants as temperatures rise and humidity drops. Before a hot, dry summer kicks in, it’s a good idea to know what to look for.
Two-spotted spider mites (Tetranychus urticae) can become a serious threat to your citrus and other fruit trees, most vegetables, and many ornamentals, such as marigolds, roses, and salvia. Beans, blackberries, blueberries, cucumber, eggplant, lettuce, peas, squash, strawberries, and tomatoes are all favorite foods of the two-spotted spider mite.
Two-spotted spider mite description
As arachnids, all mites have two body segments and eight legs. Two-spotted spider mite eggs are round to spherical, but very difficult to see. Instead, you may see the webbing used to protect those eggs. Colorless larvae, which start out with only six legs, go through two developmental stages to reach greenish-yellow, eight-legged adulthood. This transformation can occur in as little as 5 days, and females can lay 120 eggs in their lifetime, so populations can rapidly explode.
An interesting note, unfertilized eggs hatch into males, while fertilized eggs hatch as females. This is called arrhenotoky.
Males are smaller and have narrower bodies and are more active than females. These close cousins to red mites are greenish-yellow to brown, with two dark spots, and they even have a red winter phase, but you probably won’t be able to see them without a hand lens. [Those dark spots are accumulated body wastes, so they are not always visible.] At only 1/50” long, two-spotted spider mites are easier to find by looking at the damage they cause.
Damage caused by two-spotted spider mites
As sap-sucking pests, similar to citrus mealybugs and citrus bud mites, these mites pierce plant cells and remove the contents. Hidden from view by feeding on the underside of leaves, they often go unnoticed until the damage becomes obvious. Mite feeding causes stippling and bleaching. These damaged areas increase, causing bronzing and early leaf drop. If you look at the underside of these leaves, you will often see the cast-off exoskeletons of mites. You may also see extensive webbing over buds, stems and flowers. Extensive feeding can cause stunting and even plant death.
How to manage two-spotted spider mites
Since two-spotted spider mites feed on such a wide range of plants, they are difficult to control. Mites favor feeding on stressed plants, so proper feeding and irrigation can help your plants seem less appealing to these pests. In addition, you can use these tips to reduce problems caused by two-spotted spider mites:
Predatory mites, such as Phytoseiulus persimilis, ladybugs, minute pirate bugs, and lacewings are all beneficial insects that feed on two-spotted spider mites, so keep you yard hospitable to these helpful predators. Mites are developing resistance to most chemical pesticides, but insecticidal soaps are effective against mites, with horticultural oils (not dormant oils) coming in a close second. These treatments are only affective against the mites that come into contact with it, so repeat treatments are often necessary.
If you have a walnut tree, you should know about walnut scale. Even if you don’t, this is still an interesting read.
Walnut scale insects (Quadraspidiotus juglansregiae) have a unique behavior that makes them particularly fascinating. Like other armored scale insects, females protect themselves under round, dome-shaped covers. But walnut scale takes this concept to a whole new level.
Walnut scale lifecycle
Female walnut scale insects lay eggs in spring. These eggs hatch in only 2 or 3 days. Female crawlers move around a little bit, searching for a good spot to set up household. Once a spot is selected, they begin feeding and start building their protective cover.
Male crawlers wander around, looking for a female. When they find one, they huddle up next to her, tucking themselves under the edge of her ‘skirt’, where they excrete their own elongated scale coverings. This often creates a daisy-shaped cluster of scales.
After these groups mate, those females lay the year’s second batch of eggs. These eggs hatch, usually mid- to late summer, and stay in the crawler stage over winter. In spring, females claim real estate and males emerge with wings, which they use to find a female.
Walnut scale description
Walnut scale coverings start out white. This is called the white cap stage. Then they darken to grey or brown within a week or so. If you lift the covering off the central, round female walnut scale, you would see a yellowish body with indented margins. Other scale insects do not share those characteristics.
Damage caused by walnut scale
Like other scale insects, walnut scales use piercing mouthparts to suck plant juices from the cambium layer of twigs and branches. This weakens the tree, leading to branch dieback, cracked bark, and reduced harvest. Walnut scale feeding also increases the likelihood of canker development and fungal diseases caused by Botryosphaeria.
How to control walnut scale
You can’t control them if you don’t know they are present. Make a point of inspecting your trees regularly for signs of infestation and infection. You can apply sticky barriers near walnut scale adults to capture crawlers, as they emerge. There are many beneficial predators that feed on scale insects. Parasitic wasps, twicestabbed lady beetles, and a tiny black beetle that goes by the name Cybocephalus californicus, in particular, love to feed on walnut scales. Commercial growers apply insecticides during dormancy or when crawlers emerge in spring.
Narrow range oils can also be used, but walnut trees are very sensitive to horticultural oils. Do not use oils on walnut during dormancy, or between bud break and shoot elongation. Oil use at these times can harm your tree. Horticultural oil can be used with caution as buds begin to swell and the tree enters the delayed dormant period. If your walnut tree is water stressed or suffering other forms of stress, do not apply oil. Oils should also never be used when temperatures are above 90°F.
Scale infestations are on the rise. This is believed to be the result of several different factors, including reduced numbers of beneficial insects. Keeping your trees healthy makes them less likely to be harmed by pests such as walnut scale.
Now you know.
After investing time and garden space to asparagus, one of the last things you want to see is something attacking your spears. Originally from Europe, this tiny fly is now found everywhere asparagus grows. While asparagus miners do not cause serious damage, they can carry a disease that will
Asparagus miner description and lifecycle
You won’t see the early life stages of asparagus miners. Whitish eggs are only 1/1000” in diameter and laid under the epidermis, at the base of asparagus stalks. Slightly larger larvae (15/1000”) are also white and tapered at both ends, with black mouth hooks. After feeding, they will grow to 1/5” in length before pupating. Pupae are dark brown and flattened and can be up to 17/100” long. These pests overwinter in the pupal stage, either in the soil or in stalks.
Adult flies are small (1/10”), shiny black and somewhat humpbacked. They have clear, tapered wings. In California, they appear in May and again near the end of the summer.
Damage caused by asparagus miners
Damage is usually seen during the fern growth stage. As they feed, asparagus miners burrow a meandering pattern just below the surface. This feeding behavior can result in girdling, which causes chlorosis. More often, the damage is mostly cosmetic.
The real problem associated with asparagus miners is that they are vectors for Fusarium root and crown rot. If you see bright yellow discoloration or wilting in your asparagus plants, it may be that asparagus miners have brought Fusarium root and crown rot to your asparagus bed. In that case, both the affected plant and the surrounding soil should be removed and thrown in the trash.
Controlling asparagus miners
Generally, parasitic wasps keep asparagus miners in check. If a heavy infestation occurs, remove the fern growth at the end of its season and throw it in the trash. Insecticides are not effective.
Now you know.
Many plant diseases are caused by viruses.
If you can get beyond their disease-carrying behavior, however, viruses are amazing things.
Most viruses are made up of half a DNA strand, called RNA, and are protected by a coat made out of protein. A small handful of plant viruses contain full DNA strands. There is another group, called viroids, which contain an RNA strand but do not have a protein coat. In a recent article, The Scientist reported that new research shows different segments of a virus’ genetic information are used to infect separate cells, creating a domino effect of plant disease. I swear, the more I learn, the more amazing the world gets! But I digress…
The science of viruses
Viruses enter a plant cell and use their RNA strand to reprogram the cell’s genetic instructions. This causes the cell to start producing more of the virus’ RNA. These new strands then infect neighboring cells, and so on.
There are several families of viruses that cause plant disease. We won’t go into that now. What’s important to know is that the common names of most viruses start with the plant most likely to be infected, followed by the most characteristic symptom. For example, bean yellow mosaic is commonly seen in beans and a yellow mosaic pattern is the most common symptom.
Symptoms of viral infection
While there are more viral diseases than I can count, many of them share similar symptoms. The most common symptoms of viral disease in plants include:
Bronzing and leaf rolling may also be seen.
Viruses are generally spread to plants through insect feeding. Common disease-carrying insects include:
Dagger nematodes and some fungi and single-celled organisms also carry viruses. Viruses can also be moved around the garden on pollen, clothing, tools, and plant debris. Many viruses overwinter in seeds, flowers, perennial weeds, and crop root systems, where they can lie dormant for years.
California’s viral diseases
There are dozens of viral plant diseases found in California. The most commonly seen include:
You can find lists of viral diseases common to other areas by contacting your local County Extension Office.
Controlling viral diseases in the garden
Healthy plants are better able to ward of viral infections. This means proper feeding, irrigation, and pruning. It also means selecting resistant plants that are suitable to your microclimate, buying only certified disease-free plants and seeds, planting at the proper depth, and avoiding mechanical injuries from rubbing branches and weed wackers, among other things.
Use an integrated pest management (IPM) program to control viral diseases. This means encouraging natural predators and parasites of viral diseases, sanitizing garden tools regularly, and using cover crops and crop rotation to interrupt disease triangles. Yellow sticky sheets can be used to trap many disease-carrying pests. Pesticides and insecticides used to kill disease carriers are not effective. Reflective mulches have been used successfully to confuse some disease-carrying pests. Diseased plants should be removed and thrown in the trash to prevent healthy plants from becoming infected.
Viral diseases of plants are on the rise, largely due to monoculture, mass production, climate change, global shipping and other human activities. You can reduce the likelihood of viral diseases affecting your plants by placing new plants in quarantine and knowing what to look for.
Now you know.
Brown soft scale (Coccus hesperidum) may be found on pomegranate and citrus trees, as well as bay laurel.
These pests can suck the life out of your lemon, orange, kumquat, lime, and pomegranate trees, killing twigs, and reducing your harvest. Like other sap-sucking insects, brown soft scales excrete sugary honeydew, which creates habitat for sooty mold, and attracts disease-carrying ants.
Brown soft scale description
These pests live under yellowish, mottled shells. They may look like nothing more than little bumps on leaves and twigs, Brown soft scale look similar to citricola scale insects.
Brown soft scale lifecycle
Brown soft scale females give live birth, or lay eggs which hatch almost immediately. These young crawlers move around freely on leaves and twigs, feeding as they go. They continue moving around until they are about half grown, molting twice.
Controlling brown soft scale
Sticky barriers around the trunks of susceptible trees can cut off protection to brown soft scale pests by ants. Also, avoiding the use of broad spectrum pesticides allows natural predators to feed on these pests. If you see scale shells with holes in the top of them, you will know they have been parasitized by beneficial insects. Heavy infestations can be treated with dormant oil in winter, but this is rarely necessary.
Psyllids are jumping plant lice that suck plant juices. There are over 160 psyllid species in California, 140 of which are native to the area.
Most native psyllid species do not pose a serious threat to your garden. Local predators tend to keep those populations in check most of the time. Invasive psyllid species are something else altogether.
Psyllids look like tiny cicadas or winged aphids, with tubular mouthparts. They have very strong legs and short antennae. Psyllids can be 1/12 to 1/5” long. Adults hold their wings in a roofline position. Nymphs are flattened and look a lot like soft scale insects. Psyllid nymphs commonly produce waxy filaments or covers, called lerps. Lerps are made from wax and honeydew.
Regardless of the species, psyllids start out as tiny eggs that hatch and go through five developmental stages, or instars, before reaching adulthood. Adult psyllids can fly, but most prefer to jump. If you see what you think is a psyllid run or fly away, it is probably a psocid [SO-sid]. Psocids are beneficial insects that feed on fungi. They differ from psyllids in that they have a narrow “neck” and chewing mouthparts.
Psyllid host plants
As a species, psyllids have strong preferences for particular host plants. While some psyllids will prefer your sweet peppers and chili peppers, other varieties will go after your peaches and nectarines, while others will only feed on olive or pear trees, and yet other psyllid species will only feed on potato and tomato plants.
The invasive Asian citrus psyllid carries huanglongbing, a deadly citrus disease. Orange, lemon, lime, kumquat, and grapefruit trees infected with huanglongbing must be destroyed by a professional. Sad, and expensive. These pests, when present, are most active April through June in the San Francisco Bay Area.
Psyllid species most likely to threaten your garden include:
There are dozens of psyllid species that infest ornamental trees and shrubs, as well. These include the recent invasions of Ficus leaf-rolling psyllids and spotted gum psyllids. On the other hand, some psyllid species are being used to our advantage. The Australian melaleuca psyllid, for example, has been purposefully introduced to Florida to help control paperbark trees, an invasive weed tree.
Damage caused by psyllids
One of the biggest problems associated with psyllids is their poop. After they have robbed your plants of valuable nutrients, weakening the plant, they add insult to injury by excreting a large portion of the sap they stole and depositing on leaves. Known as honeydew, the excrement of sap-suckers is filled with sugar and other nutrients. Honeydew ends up being food for fungal sooty mold and disease-carrying ants.
Psyllid feeding can also spread viral diseases, such as calico, bacterial diseases, such as zebra chip, galls, leaf and bud discoloration and deformation, and premature leaf drop. Leaf distortions often look similar to peach leaf curl. Pear psyllids inject fruit with toxins that blacken leaves and fruit skins. Psyllid feeding also creates points of entry for other pests and diseases.
How to control psyllids in the garden
Once psyllids appear in your garden, insecticidal soaps and yellow sticky sheets can be used to help control them. Parasitic wasps and pirate bugs can put a serious dent in psyllid populations, so avoid using broad spectrum insecticides. Severely infested plants should be removed and destroyed or thrown in the trash. Usually, simply monitoring plants regularly can make controlling these and other pests much easier.
To prevent invasive psyllids from finding your garden, only buy pest-free plants from reputable nurseries, place new plants in quarantine, and do not bring plant products that may be infested into your state, community, or yard.
Because of the risks posed by invasive psyllids, any unrecognized psyllids should be taken to your agricultural commissioner or local County Extension Office for identification.
You walk past a tree and notice leaves rolled up into neat tubes. What causes this and is it a problem?
There are several leafroller species found in California:
A quarantine is in place for the light brown apple moth. See if you live in an affected area by clicking on the CA Dept. of Food & Agriculture’s Boundary Index Map. If you live outside of California, you can contact your local Cooperative Extension Office for more information
Leafrollers start out as clusters of flat, irregularly shaped eggs often found on twigs and leaves. These egg masses are coated with a dark gray or brown glue that later bleaches to white, giving them an appearance similar to fish scales. If you look closely at an egg mass in spring, you can see tiny pinholes where larvae have hatched.
After hatching, larvae pull leaves into a cylinder for protection as they feed. Most larvae feed through summer and then overwinter as pupae, though some species continue feeding throughout the year, causing considerable damage.
When disturbed, leafroller caterpillars tend to wriggle wildly and then rappel to the ground on a single silken thread.
April is the time to start checking apple, apricot, avocado, cherry, peach, pear, plum and prune trees, and blueberries, for signs of the dreaded Pacific flathead borer.
Like other borers, these pests chew tunnels in wood, weakening a tree’s structure, and robbing it of important nutrients found in the inner cambium layer. Newly planted trees and trees weakened by drought, water-stress, scale insects, carpenterworms, or diseases, such as Phytophthora or Armillaria, are particularly susceptible. These weakened areas are then more likely to be attacked by other pests, such as shot hole borers.
Pacific flathead borer feeding can also girdle a young tree, killing it. The only symptom you may see is a dark colored depression in the bark, or tiny cracks where you might see frass (bug poop), usually on the side receiving the most sunlight.
Pacific flathead borer identification
Pacific flathead borers (Chrysobothris mali) are flattened, wedge-shaped, dark bronze beetles that can be 0.5 to 0.75” long. You may see copper-colored spots on the wing covers.
Eggs are very tiny, only 0.04” in diameter, flattened, oval, and white. Larvae grow to 0.75” in length and are white, with an amber colored head. Larvae are flattened, with a widened area just behind the head, tapering towards the rear end. Pupae are also whitish and flattened, getting darker as they mature.
Pacific flathead borer lifecycle
These pests overwinter in a prepupal stage. As temperatures begin to rise, they pupate. From April through July, adult beetles emerge, usually beginning around the same time apple trees are blooming. Then females mate and begin laying eggs in the bark, favoring areas weakened by sunburn or mechanical injury from tree supports, weedwackers, and out of control lawn mowers. When the eggs hatch, larvae burrow directly into the bark and begin feeding on the nutrient-rich cambium layer, robbing your trees of the nutrients they need to grow and produce fruit. As the larvae mature, they will either create a pupal chamber in the xylem, or burrow under the bark, where they will stay until the following spring.
Pacific flathead borer controls
Healthy trees are better able to resist and recover from Pacific flathead borer attack. This means selecting trees suitable to your microclimate, planting them at the proper depth, and feeding, irrigating, training, and pruning them properly.
Since eggs are laid in weakened bark, protect trees from mechanical injury, and be sure to whitewash exposed bark before sun damage can occur.
Birds, especially woodpeckers, will find and remove Pacific flathead borers, and carpenter ants eat both larvae and pupae. Insecticides are commonly used in commercial orchards to kill new larvae, but once the larvae are inside the tree, there is nothing you can do besides pruning out infested wood and burning it.
Now you know.
Ashy stem blight, also known as charcoal rot, is a fungal disease of cucurbits. This means that your melons, squash, and cucumbers are susceptible. It can also affect common beans, blackeyed peas, lima beans, chickpeas, corn, fenugreek, soybeans, sorghum, and sunflowers.
Ashy stem blight is a soil borne fungus (Macrophomina phaseoli) that loves hot days (> 85°F) and cool nights. This pathogen can stick around for up to 12 years. It is common in California and often infects plants within 2 weeks after being planted, but symptoms generally do not appear until much later in the growing season, as temperatures begin to rise - after you’ve invested weeks of irrigation, feeding, and weeding. So, learning how to recognize and prevent this disease can help ensure a better harvest.
Symptoms of ashy stem blight
The first sign of ashy stem blight are black, water-soaked lesions or cankers along the stem at the soil line, stunting, and chlorosis (yellowing) of the upper, or crown leaves. If you look closely at the lesions, you may be able to see concentric rings. Infected pods may ripen prematurely. As the fungi population grows within the plant, you may see an amber gum oozing from the infected plant. Eventually, the stem turns dry and brown. If lesions girdle the plant, it will die. If you dig up an infected plant, you will see blackened roots and a lack of feeder roots.
Preventing ashy stem blight
Ashy stem blight is known as a “stress pathogen”. This means it preys on stressed plants. Stresses, such as a heavy fruit load, high temperatures, drought, and water-stress can make plants more susceptible to infection. Keeping your plants healthy can help them protect themselves.
While furrow-irrigated plants rarely have severe cases of ashy stem blight, you may be surprised to learn that the disease is common with drip-irrigated systems. It is believed that this particular set-up increases salt levels near the soil surface, creating salt stress.
Monitor plants regularly for signs of infection. Once infection occurs, affected plants should be removed and thrown in the trash, and a 3-year crop rotation with non-susceptible crops should be put into place. There are no effective chemical treatments for this disease.
Now you know.
We’ve all heard that beans cause gas, but did you know beans rust? Well, not rust like the undercarriage of a New England truck, but rust just the same.
Bean rust, like other plant rusts, is a fungal disease. Rust is found worldwide and it can wipe out your bean crop if it takes hold early enough in the growing season.
California’s cool, wet springs are just the conditions needed for rust to thrive. Add overhead watering or a decent breeze and the stage is set for an epidemic. Fungi are so efficient that, under ideal conditions, the disease cycle can be repeated every 10 to 14 days!
There are several strains of bean rust. Two of the most common are Uromyces appendiculatus and Uromyces phaseoli typica, but you don't need to know the Latin to recognize bean rust in the garden.
Bean rust symptoms
Similar to other rusts, bean rust prefers moist places and moderate temperatures (65 to 85°F). While it can occur on any aboveground portion of a plant, bean rust is most commonly found on the underside of leaves. Pods can also be affected. At first, it just looks like tiny white or yellow bumps. Then those bumps break open and turn into bright orange, reddish, or yellowish flecks. Those flecks are pustules that are made up of more fungal spores than any of us cares to count. [Okay, some scientists love counting things like that.] A yellow outer ring is sometimes visible. Leaves may begin to curl downward and plants may develop a scorched appearance. These symptoms are easy to see and make identifying the condition simple. Getting rid of it is something else all together.
Bean rust control
The fungi that cause bean rust can be spread by ants, aphids, and gardeners. It can stick to tools, fingers, and clothing. As with many other plant diseases, prevention is far easier than eradication. Use these tips to prevent and control bean rust in your garden:
Keep in mind that rust pustules are easily dislodged and can land somewhere else, or on the soil, where they can be bounced back up into your plants by rain, wind, and overly exuberant irrigation. And be sure to disinfect your tools after removing rust-infected leaves, to avoid spreading the fungus to healthy plants.
With a name like Halo, you might expect little cherubs in today's post, but that is not the case. The bacteria responsible for halo blight are no angels.
In common blight, those lesions have wide, lemon-colored borders, and they continue to grow. Bacterial brown spot lesions have narrow light green borders and the centers tend to dry out and look tattered. Halo blight lesions tend to stay small and they have prominent light green halos, hence the name.
Leaves are not the only place damage occurs. Pods can also become infected, making them inedible. Pods infected with common blight have lesions with red or rust colored borders, while symptoms of the other two diseases are difficult to distinguish from each other, both being the same water-soaked lesions seen on leaves.
Managing halo blight
As with other diseases, prevention is the easier way to go. Since moisture is needed for halo blight to develop and spread, avoid overhead watering and save the sprinklers for your lawn. Furrow irrigation will get water to the roots without creating a potential disease site. This is especially important when temperatures are between 68 and 74°F (20 to 23 °C). Unlike many other blights, halo blight bacteria prefer these slightly cooler temperatures.
Also, be sure to start with certified disease-free seed, and place new plants into quarantine before exposing the rest fo your garden to whatever they may be carrying. Speaking of carrying disease, the bacteria responsible for halo blight can also travel on rain splashes, wind, pet fur, shoes and clothing. If you have been exposed to halo blight, you might want to change your clothing and swap shoes to avoid spreading the disease throughout your garden. Finally, when your bean plants have completed their life cycle, cut them off at ground level, leaving soil microorganisms in place, and add plant debris to the compost pile. Leaving plants to break down in the garden can provide potential overwintering sites.
Fixed copper or Bordeaux mixture may be used to prevent halo blight. Plants infected with halo blight should be removed and destroyed, followed by a 2 to 4-year crop rotation program.
Bean common mosaic is a viral disease caused by several different virus strains. Close cousin to bean yellow mosaic and clover yellow vein virus, bean plants can be unfortunate enough to be infected with all three at the same time.
What’s really fascinating about this disease is that there are two different sets of symptoms that may occur.
Symptoms of bean common mosaic
Bean plants infected with these viruses may come down with bean common mosaic or bean common mosaic necrosis.
Bean common mosaic is very common in California. It appears as mosaic patterns of light and dark green on the leaves. Puckering, blistering, rolling, and downward cupping are also common symptoms. Plants infected while young will also be stunted.
Bean common mosaic necrosis has not been seen in California since its first sighting in 1996, but you’ll want to be on the lookout, just in case. Symptoms include small, reddish-brown spots on the leaves. Nearby leaf veins become brown or black and this necrosis (death) then spreads to the phloem and throughout the plant, ultimately killing it. It you take a cross-section of an infected stem or pod, you will see reddish streaking in vascular tissue. These symptoms look very similar to black root rot and Fusarium wilt, but neither of these conditions cause streaking in the pods.
In both cases, leaves may also be smaller than normal, and blossoms and pods may be deformed. Which set of symptoms your plants will exhibit depends on which virus is involved, and whether or not your plants have dominant or recessive genes, or if one gene is present at all. Plants with the dominant gene are resistant to common mosaic, but hypersensitive to common mosaic necrosis. Some bean varieties, which lack the gene altogether, have symptoms which could fall under either category. Symptoms of bean common mosaic are most likely to appear when temperatures are between 68 and 77°F.
Bean common mosaic transmission
The bean common mosaic virus overwinters in infected seeds and weeds. The virus is most often transmitted on pollen and by aphids. It can also move from plant to plant on clothing, tools, and plant debris.
The best way to avoid introducing this virus into your garden is to:
Resistant bean varieties
According to UCANR, these varieties are resistant to one or more strains of this virus:
Once these viruses are in your soil, they are difficult to get rid of - it is far better to start with clean seeds and do what you can about those pesky aphids.
You don’t have to grow tobacco to have reason to worry about tobacco mosaic virus.
Tomatoes are highly susceptible to this disease that can be carried on tools, clothing, cigarettes, and, yes, even the saliva and other bodily excretions of smokers. This tenacious virus can stay alive even after its host is dead, and it can withstand extreme temperatures.
Tobacco mosaic virus host plants
In addition to tomatoes and tobacco, the tobacco mosaic virus (TMV) has been found on over 350 different plant species, including cucumbers, many flowers and ornamental plants, and all members of the nightshade family, such as eggplant, potatoes, groundcherries, tomatillos, and peppers. While they may not show symptoms, grapes and apple trees can also become infected.
Symptoms of tomato mosaic virus
Tobacco mosaic virus starts out as nothing more than paler than normal green between the veins of young leaves.
This lightened area quickly becomes mottled, leaving a green, white, or yellow mosaic pattern. Bumpy wrinkles may also appear, in a behavior known as rugosity, and leaves may appear distorted or stringy, or exhibit cupping.
Leaf veins may also turn yellow, and yellow streaking on the leaves may also occur. Many of these symptoms can be mistaken for signs of chemical overspray, but the mosaic pattern is usually distinct enough to rule this out. While this disease does not kill plants, it can stunt them severely. Infected leaves soon die, leaving dead patches in the plant and reducing production by up to 20%. Fruit that is produced is often discolored and deformed.
How is tobacco mosaic virus spread?
Unlike many other diseases, which are spread by sap-sucking insects, such as thrips and aphids, tobacco mosaic virus is mostly spread by direct contact. Tobacco mosaic virus has also been spread by chewing insects, such as grasshoppers and caterpillars, and by bumblebees, as they pollinate flowers.
Preventing tobacco mosaic virus
Plants infected with tomato mosaic virus must be removed and destroyed. According to the Michigan State University Extension, you can prevent the virus from moving onto uninfected plants by spraying them, just before transplanting, with a 20% nonfat dry milk solution. This spray can also be used on containers, walkways and other surfaces. The milk solution coats the virus, rendering it inactive. The milk treatment only works while the milk is wet.
These other tips can also help reduce the likelihood tobacco mosaic virus in your garden:
*Check plant labels for the letters V, F, N, T or A. These symbols indicate a resistant to verticillium wilt, fusarium wilt, nematodes, tobacco mosaic virus or alternaria stem canker, respectively.
According to a study conducted by the National Institutes of Health, all brands of cigarettes studied tested positive for tobacco mosaic virus, while only 53% of those viruses were viable. Also, 45% of the saliva samples taken from smokers tested positive for tobacco mosaic virus. So, smokers and users of other tobacco products, please wash your hands before entering your (or someone else’s) garden, and always throw your butts in the trash. Thank you.
You can grow a surprising amount of food in your own yard. Ask me how!