Healthy soil is teeming with microscopic life. Most soil organisms are beneficial, but some of them carry disease. The more you know about soil borne diseases, the better you can protect your plants.
The biggest problem with soil borne diseases is knowing they are there. You can’t see the pathogens. Damage can be done before you know anything is wrong. Also, symptoms of soil borne diseases can look a lot like nutrient imbalances, chemical overspray, and poor environmental conditions. This is why it is so important to monitor your plants regularly.
Fungi and nematodes are behind most soil borne diseases, but there are other players and some of them are relatively new discoveries.
Nematodes are microscopic, unsegmented worms. Some of them are beneficial and some carry disease. Beneficial nematodes kill cutworms and corn earworm moths. Disease-carrying nematodes include needle nematodes, root-knot nematodes, and stubby root nematodes. The real problem with nematodes is that there are so many of them. It is estimated that, for every person on earth, there are 60 billion nematodes. [Thank goodness they aren’t all bad!]
There is another class of soil borne disease carriers called Phytomyxea [FI-toe-muh-kia]. Scientists used to think they were a type of slime mold, but genetic testing and electron microscopes have taught us that they are their own group. Phytomyxea are plant parasites that can cause clubroot in cruciferous vegetables and powdery scab in potatoes.
Bacterial diseases are less likely to be soil borne because bacteria have a hard time surviving in the soil. Also, they need a wound or natural opening to get inside your plants. That being said, the following soil borne diseases can occur in your garden:
Soil borne viral diseases are rare. In most cases, they are transmitted by nematodes and certain fungi. Soil borne viral diseases include lettuce necrotic stunt and wheat mosaic, which causes stunting and mosaics in wheat, barley, and rye.
How to prevent soil borne disease
In nature, plant diseases rarely get out of hand. Soil pathogens are usually kept in check by other organisms and plants’ defense mechanisms. However, as we select plants, spray chemicals, and stir up the soil, we interrupt those protections. The main cause of soil borne diseases taking hold is an imbalance in soil populations. Reduced biodiversity gives pathogens the upper hand.
One way to reintroduce that biodiversity is by top dressing with aged compost. Research has shown that top dressing with aged compost is very effective at suppressing soil borne diseases in greenhouses, though less so in the field. In both situations, the more compost was added, the more effective it was. Interestingly enough, if the compost was sterilized beforehand, it was less effective. I think we can assume the effect is at least partially biological.
As with most diseases, three factors must be present for a problem to occur: the host plant, the pathogen, and the right environmental conditions. This is called the disease triangle. Remove any one of the three and the disease is prevented or controlled. Crop rotation is an excellent way to break this disease triangle. Your rotation schedule will vary depending on the disease.
While you can, in some cases, apply treatments directed toward specific pathogens, they don’t always work. Most of these treatments consist of other microorganisms that prey on the pathogens. These only work if your soil already has everything the introduced microorganisms need. Funny thing is, if all those things were already there, so would most of the predators. Biodiversity is your friend. In fact, mycorrhizal fungi (good guys) often create protective mats which contain antibiotics and pathogenic toxins around plant roots, all while helping your plants absorb nutrients.
Use these tips to prevent soil borne diseases in your garden:
Finally, as tempting as they may be, chemical treatments are rarely a good choice for backyard gardeners. Pathogens are developing resistance to these treatments which means stronger chemicals must be used. Whenever possible, use some other method of controlling soil borne diseases.
Cedar chests repel moths. Adding pencil shavings to potted plants repels or kills insect pests, such as ants, carpet beetles, cockroaches, fleas, mosquitos, moths, spiders, and termites. At least, that’s what they say.
Can we really use cedar as an insect repellent? It sounds (and smells) so nice…
Let’s start by learning a little more about what we mean when we use the word cedar.
Cedar is a conifer. The word ‘cedar’ refers to any of five Cedrus trees, all of which produce oils said to repel moths whose larvae eat fabrics, such as wool. These are ‘true cedars’, none of which are native to North America. Other trees lumped together with Cedrus are the Thuja, or cypress trees, three of which are native, and a few juniper trees. Cedar, cypress, and some junipers do contain chemicals, known as terpenoids, which are used to protect themselves against insect pests. The terpenoids used by cedar and cypress are not the same, however. Cedars use terpenoids called sesquiterpene hydrocarbons, while cypress and juniper use something called thujone. Thujone is also found in common sage, some mint species, mugwort, oregano, tansy, and wormwood. In both cases, some insects are repelled while others are not.
Insects and cedarwood oil
Your grandmother was right about her cedarwood hope chest - it really does repel clothes-eating moths. It does nothing, however, against fleas, mosquitos, spiders, and most ants. In its defense, if you have ordorous or Argentine ants, cedarwood oil will help keep them away. It will also repel or kill carpet beetles, cockroaches, and termites, none of which are a threat to your plants.
Dangers of cedarwood
Before you jump on the cedarwood oil bandwagon, however, you need to know that there is a downside. Research has shown that, while exposure to cedar wood oils can interrupt the reproductive and developmental cycles of peanut trash bugs, Indian meal moths, and forage mites, prolonged exposure to these oils increases your chances of getting cancer.
Strangely enough, European turnip moth larvae love eating cedar. Isn’t life weird?
Your tree may house a tiny, fungi-farming beetle called the polyphagous shot hole borer, but I hope not.
Native to southeast Asia, these invasive beetles are threatening trees in Israel and California with Fusarium dieback. Fusarium dieback is a fungal disease that blocks the flow of water and nutrients through a tree’s vascular system. And polyphagous shot hole beetles actively farm those particular fungi. We will get to that in a minute.
Polyphagous shot hole borer identification
Polyphagous shot hole borers (Euwallacea fornicatus) are smaller than a sesame seed. You could fit 6-10 females, end-to-end, across a dime. Females are black and males are brown and wingless, but you will probably never see a male. Sightings are rare and no wonder. Males stay in the galleries and you could fit 12-18 of them across the face of a dime.
Polyphagous shot hole borers look identical to another invasive borer called the Kuroshio shot hole borer, or tea shot hole borer (Euwallacea fornicatus). The tea shot hole borer prefers tea plants in Sri Lanka, while the polyphagous shot hole borer appears to have a voracious appetite for over 110 tree species. [The word polyphagous means eats many things.]
Host trees and signs of infestation
Traditionally, polyphagous shot hole borers tended to only infest dead or dying trees. Having been accidentally introduced to new regions, these pests have developed a taste for healthy trees. Once trees are infected, they can die. Host trees include:
External symptoms of infestation often look innocuous. Slightly weepy, small damaged areas of the bark, the presence of white frass, maybe a little sawdust or sugar volcano action is all you can see from the outside. If you look very closely, you may see several exit holes, about the size of the tip of a ballpoint pen. The inside of an affected tree is something else entirely.
Polyphagous shot hole borers chew holes that penetrate 1/2” to 1-1/2” into the wood. Then they start burrowing, creating galleries. Black flecks and tunnels can be seen throughout an infested tree. These black areas indicate where Fusarium fungi are being farmed.
Polyphagous shot hole borer as farmers
Polyphagous shot hole borers are a type of ambrosia beetle. Rather than feeding on bark or wood or sap, ambrosia beetles eat fungi that they grow for themselves. Polyphagous shot hole borers have tiny pockets on their exoskeleton. In these pockets, they carry spores of the Fusarium euwallaceae fungi. After burrowing into a tree, the borer starts growing these fungi along the walls of the burrowed galleries. The fungi provide adult and larval forms of polyphagous shot hole borers with food in a protected environment and the borers carry the fungi to new trees. It's a win-win situation for them. The problem is, this fungi causes Fusarium dieback. Fusarium dieback causes branch dieback, canopy loss, and it can kill trees.
Polyphagous shot hole borer management
Yellow sticky cards, purple prism traps, and multiple funnel traps have been used with some success. Because polyphagous shot hole borers have no natural enemies here in California, and because they live inside the tree, safe from insecticides, prevention is worth the effort.
Polyphagous shot hole borers are most commonly spread on firewood. If infested trees are chipped into mulch, the borers can catch a ride to your trees, so always inspect wood chips before accepting them. Wood chips cut into pieces smaller than 1” are generally considered safe because the borers get chopped up too. Personally, if I saw black galleries, I would refuse delivery just in case.
If you suspect polyphagous shot hole borers have found your trees, please contact your local County Extension Office right away.
Conks are woody, shelf-like structures produced by some fungi. These fruiting bodies are often seen on trees and they can indicate fungal diseases, such as canker rot.
Conks are the reproductive form of a large group of fungi known as polypores. Polypores are mostly found in the bark, trunks, and branches of trees, though some are found in the soil. Polypores play major roles in the decomposition of wood, so their presence often indicates decay. Polypores are also important in nutrient cycling, so they aren’t all bad. This is a large, diverse group but they all have conks in common.
The conk clan
This group is defined, not by genetics, but by growth behavior, so it is very diverse. The most common types of conks include:
Also known as bracket fungi, or shelf fungi, this group (Basidiomycota) produces circular, shelf-shaped fruiting bodies that can appear in rows, columns, or singly. Basidiomycetes are the only fungi known to break down lignin. Lignin is what makes trees rigid and hard. The disease that accomplishes this feat is known as white rot.
Some conks are annuals while others are perennials, some of which can live for 80 years or more. In either case, they tend to be tough, leathery, sturdy growths. These growths produce spores, called basidiospore, in pores found on the underside of the conk.
Conks appear to grow directly out of the wood on which the fungi feed. If you were to cut one open and look at it closely, you would see two layers: a tube layer and a supporting layer. The tubes are honeycomb-like structures lined with a spore-forming surface, called the hymenium, and the supporting structure creates the shelf and its attachment to the tree.
The problem with conks is that their presence indicates that some sort of fungi has taken up residence in your tree. If your tree has conks, the first step is to identify the type. Some fungi are worse than others.
Preventing fungal conks
The fungi that produce conks generally enter trees through mechanical wounds, damaged roots, broken or rubbing branches, frost cracks, sunburn damaged bark, and improper pruning. Fungal spores travel on the wind, rain, and on birds and insects, so keeping your tree’s protective outer layer intact is the best prevention. This means you should:
If you have a tree with conks, you should probably contact a certified arborist. They can inspect the tree for structural integrity and to determine the extent of the infection.
Conks may look cool, but you don’t want them on your trees.
Can you see a crack in the trunk or branches of your tree? It may be canker rot.
Canker rot is a collection of fungal diseases that eat away at the interior of tree trunks and branches, weakening the tree and setting the stage for other pests and diseases. Canker rots can also girdle your tree and kill it. While most commonly seen in ornamental trees, canker rot can occur in apple and other fruit and nut trees. Trees with canker rot can be extremely dangerous and should be dealt with right away.
Canker rot identification
Cankers are open wounds, or lesions. Cankers can be a few inches long and wide, or several feet long, depending on the fungal species. The bark next to these cankers dies, becoming discolored, often lighter or orangish, and it is tightly bonded to the canker. After a year or so, the dead inner bark turns black and stringy. This looks a lot like sooty bark canker, but canker rot can also have lenticular (lens-shaped) lighter areas in the bark. Unlike other canker diseases, canker rot affects both bark and inner tissue.
Canker rots can also cause swelling, sunken areas, gnarled bark, and conks. Conks are shelf-shaped fungal fruiting bodies. After spores are released, the conk will dry out and darken. It may remain on the tree or fall off.
If you were to see inside your tree, you would see that the heartwood and sapwood have become discolored. Instead of the warm, rich yellowish-browns of healthy wood, you would see gray, orange, or even pink-tinged wood, often extending 3 or more feet beyond the canker.
Canker rot lifecycle
The fungi responsible for canker rot usually enter trees through pruning cuts and wounds. Fungi attach to the wood and then move to the cambium to access the water and nutrients flowing through the vascular bundle. This is what causes the canker. The fungi also move to the bark, where they eject spores, which are then carried on wind to nearby trees.
How to control canker rot
As always, healthy trees are better able to protect themselves. This means selecting species suitable to your microclimate, planting them at the proper depth, irrigating and fertilizing your trees properly, and monitoring for signs of problems. Other actions you can take to reduce the chance to canker rot occurring in your trees include:
Canker rot can make your tree dangerous. If it is a large tree and the canker is directly facing or opposite the prevailing wind, your tree can be blown over. Large trees weigh several tons and can be extremely dangerous. If you suspect canker rot, call a licensed arborist right away.
Prune limb borers can damage stone fruit trees, such as almond, apricot, cherry, nectarine, and peach, as well as oak. Gumming and reddish orange frass are common signs of prune limb borer infestation.
Prune limb borers (Bondia comonana) are not as common as American plum borers, but it is a good idea to know what to look for, just in case.
Prune limb borer description
Prune limb borer moths are not very large. They have a 3/4” wingspan. The forewings are grey with black and brown markings. Like many grubs, prune limb borer larvae are dull white or pinkish with a large, dark head. They are usually 1” long.
Prune limb borer lifecycle
Prune limb borer larvae overwinter inside your trees in cocoons. In spring, adult moths emerge and mate. Female prune limb borers lay their eggs on callus tissue, where narrow crotches between branches create wrinkled bark, near graft unions, and on crown galls. Eggs are also laid in wounds from pruning, tree supports, or poorly aimed weedwackers. There can be as many as four generations each year.
Prune limb borer damage
It is prune limb borer larvae that do all the damage. As soon as eggs hatch, larvae begin burrowing into the host tree. Erratic tunnels between the bark and cambium layer interrupt the flow of water and nutrients and weaken the tree structurally. Heavy infestations can weaken scaffold branches, making them likely to break off in strong winds and when supporting heavy crop loads.
Prune limb borer management
Mature, healthy trees can often withstand a prune limb borer or two, but young trees can be killed by heavy infestations. Like other borers, these pests are easier to prevent than control. Inside the tree, they are safe from predators and pesticides. Use these tips to prevent prune limb borers from taking up residence in your trees:
Over-the-counter pesticides and insecticides are not effective against prune borers. If you have a badly infested tree, it may be worthwhile to hire a professional to apply a residual, contact insecticide.
Clearwing moths are a family of pests that attack many fruits trees, as well as currants and gooseberries. These pests are often mistaken for burly wasps.
There are several different clearwing moth pests and they attack a wide variety of ornamentals and edibles. They include:
Clearwing moth identification and lifecycle
One of the most obvious ways to identify adult clearwing moths is to look at their wings - they are clear. Mostly, anyway. Adults only live for one week, so you don’t get many chances to see them. Front wings tend to be narrow and rear wings are stubbier and wider. Their yellow and black bodies look similar to yellowjackets. This mimicry continues with a behavior commonly seen in wasps, in which both species will periodically run while fluttering their wings. Unlike wasps, clearwing moth adults can also be red, orange, or even dark blue, depending on the species.
As soon as females emerge from their pupal cases, they emit pheromones to attract males. After mating, females lay tiny pale pink to reddish eggs in rough areas of the bark, in wounds, and in cracks and crevices created where branches and twigs fork. One to four weeks later, larvae emerge and the damage begins. Clearwing larvae are 1” to 1-1/2” long, with white to pink bodies and dark heads. They look very similar to American plum borer larvae. Larvae will feed heavily until they are ready to pupate.
Most clearwing moths pupate under bark. The peachtree borer pupates in the soil. Clearwing pupal cases also look a lot like American plum borer pupae, as well as carpenterworm pupae. American plum borers (Euzophera semifuneralis) tend to be found where main scaffold branches join the trunks of ash, olive, and sycamore trees. These pupal cases are thin-walled and brown, and they look very similar to those of bark beetles, longhorned beetles, roundheaded wood borers, flatheaded wood borers, and metallic wood borers. These pupal cases are often found, after they have been vacated, protruding from bark or on the ground under a tree.
Basically, anything burrowing in your trees is bad news.
Damage caused by clearwing moths
Clearwing moth larvae start burrowing into bark, cambium or heartwood of their host tree as soon as they hatch. This burrowing creates galleries that weaken the tree and make it more susceptible to other pests and diseases. It also interrupts the flow of water and nutrients throughout the vascular tissues. Branch die off can also occur. All this burrowing can make bark look gnarled.
Where these galleries occur can help you identify the species. Peachtree borer larvae are most commonly found within a few inches of the soil. Ash borer larvae prefer being 5 to 10 feet up.
In some cases, no controls are needed. Sycamore borers and western poplar clearwings apparently don’t do enough harm to require management. The other species, however, can serious harm your trees.
Since healthy trees are better able to withstand attack, proper feeding and irrigation go a long way toward minimizing clearwing damage. Whitewashing tree trunks and exposed branches reduces sunburn injury. If your soil is compacted, apply a thick layer of mulch or install a ground cover to help aerate the soil. This will help keep your trees healthier, just make sure the mulch or ground cover are kept a few inches away from the trunk to prevent fungal disease. Also, avoid injuring trees with lawn mowers, weed wackers, and other landscape equipment and tools, and remove tree stakes as soon as they are no longer needed.
Pheromone lures can be used to monitor for these pests. Just keep in mind that using pheromone lures attracts pests. These lures interfere with mating, so they can reduce clearwing populations, but this method requires an intensive, ongoing program of pheromone use. It’s probably not worth the effort for backyard trees. You can also buy pheromone traps for peachtree borers and ash borers. If using pheromone traps, be sure to follow the manufacturer’s directions exactly.
Monitoring trees every week for signs of burrowing and pupal cases is an easy way to protect your trees. You may see partially emerged pupae, which can be crushed or skewered with a piece of wire. Gumming around the base of the tree may also indicate peachtree borers.
Beneficial insects, such as braconid wasps, will kill or parasitize clearwing moths and their larvae, so avoid using broad spectrum pesticides and insecticides. Also, you can buy certain nematodes (Steinernema carpocapsae and S. feltiae) to kill peachtree borer, redbelted clearwing, sycamore borer, and western poplar clearwing. Again, follow the directions exactly for the best results.
If a truly valuable tree has a bad clearwing infestation, you should call a licensed pest control applicator. They have access to chemicals that you do not. Most over-the-counter clearwing controls are not effective.
Whether you call them chickpeas, Bengal grams, Egyptian peas, or garbanzo beans, you definitely do not want them infected with this fungal disease. Ascochyta [ask-uh-SHOO-tuh] blight, also known as blackspot, is a major disease of garbanzo beans.
Not to be confused with the other black spot (Diplocarpon rosae), which primarily affects leaves, Ascochyta blight can infect any aboveground portion of your chickpea plants, as well as your lawn. Lawns infected with Ascochyta blight suddenly develop brown patches of dead-looking grass. Ascochyta blight is caused by Ascochyta rabiei (formerly known as Phoma rabiei).
Ascochyta blight symptoms
Brown lesions that start at the base of seedlings may start out looking like damping-off disease, but these lesions continue to move up the plant, eventually affecting everything aboveground.
Infection may also first appear on leaves and work its way elsewhere on the plant. Foliar infections start out as light brown spots. Once the fungi start reproducing, you will be able to see tiny black, raised dots within these brown spots. These black dots will appear in circles of their own.
Stem lesions can cause the plant to fall over. Pod lesions reduce seed production and can cause seed shrinkage and discoloration.
Ascochyta blight lifecycle
In California, garbanzo beans are generally planted in November. This sets them up for Ascochyta blight because the spores grow best in cool, damp weather. Temperatures between 68°F and 77°F are ideal for this disease to develop. There are different forms of this fungi. One form is airborne, while the other is spread by rain and irrigation water. When these two forms meet under optimal conditions, the disease begins.
Ascochyta blight management
Ascochyta blight can be spread by infected seeds, so always start your garbanzo bean crop with certified disease-free seeds. Do not use that bag of garbanzo beans from the grocery store. The price might be appealing and those seeds are safe to eat, but they may also carry any number of pests and diseases that might take years to get rid of. You can also select disease resistant varieties. According to UCANR, the following varieties of garbanzo are currently resistant to Ascochyta blight: Sierra, Dylan, Sutter, San Joaquin, and the Airway Farms (AWF) series. That resistance can and will change because fungi evolve faster than plants.
At the first sign of infection, the affected plant should be removed and tossed in the trash. You don’t want to leave infected plant material in the garden or compost pile because this can simply spread the disease to more plants.
Ascochyta blight does not survive in the soil, so crop rotation is a good way to break the disease cycle.
If Ascochyta blight has been a serious problem in past years, space plants out more for better air flow, and plant seeds as late in the season as possible.
Fungicides can be used at the first sign of disease and reapplied according to package directions.
Stink bugs have shield-shaped bodies and most of them are plant pests. The rough stink bug, however, occasionally eats pests!
As true bugs, rough stink bugs (Brochymena sulcata) are cousin to aphids, leafhoppers, and scale insects. There are several different subspecies of rough stinkbug and none of them are 100% beneficial.
Rough stink bug identification
Their classic stink bug shield-shaped body is rather flattened and a bumpy mottled grey and black. This coloration makes them blend in well with bark. They average 1/2” to slightly more than 3/4” in length.
Do not confuse rough stink bugs with brown marmorated stink bugs (Halyomorpha halys.) or consperse stink bugs (Euschistus conspersus). Brown marmorated stink bugs are relatively new to California and pose a serious threat to gardens and orchards. They have white bands on their antennae and legs, the front of the head is more blunt than other species, and the thorax is smooth. Consperse stink bugs have no banding on the antennae, but dark spots on the legs, the thorax is smooth but somewhat convex, and this species is smaller than others.
Rough stink bug diet
Like other stink bugs, a rough’s favorite foods are plant-based. While other species prefer fruits and vegetables, the rough stink bug diet is predominantly the leaves and developing seeds of ash, boxelder, walnut, willow, and many other trees. The thing that makes the rough stink bug beneficial is that they also feed on caterpillars and leaf beetle larvae.
Rough stink bug lifecycle
Rough stink bugs spend their winters hidden under logs or the bark of trees. They may also try to get in your home. If they do, keep in mind that their name is an important clue. If you vacuum them up or squash them in your home, there will be consequences. Stinky ones. Instead, sweep them up with a dustpan and drop them into a container of soapy water or feed them to your chickens.
As spring temperatures rise, rough stink bugs become active again and start looking for a mate. Mated females lay clusters of 10 to 20 white, elongated eggs before they die. Two weeks later, the eggs hatch and pale colored nymphs emerge and begin feeding. There is one generation per year in most regions.
In most cases, getting rid of stink bugs is a good idea. The rough stink bug is an exception.
Insect pests can damage garden plants by feeding on them, burrowing into them, or by carrying diseases.
Ants, aphids, scale insects, mites, thrips, psyllids… the list never seems to end! Practically any time of year, one sort of insect or another is trying to take a bite out of your garden plants. If that weren’t bad enough, many of these pests spread diseases as they feed and travel around. There isn’t a gardener alive who hasn’t wished for an easy solution to the constant onslaught. But easy solutions often backfire and insecticides are a perfect example.
How insecticides work
Insecticides are formulated to repel, kill, or otherwise harm insects. These agents are classified as either systemic or contact insecticides. Systemic insecticides are absorbed by the plant, making it toxic to anything that eats it. Systemic insecticides have residual, long term actions, while contact insecticides have no residual actions. Contact insecticides simply have to come into contact with an insect to be toxic.
The mode of action by which an insecticide works is important as it determines which other living things may be affected. Some insecticides work by damaging an insect’s nervous system, interrupting feeding and reproductive behaviors, while other insecticides attack the exoskeleton. A damaged exoskeleton allows insects to dry out, causing death by desiccation. Growth regulators (e.g., pyriproxyfen, methoprene) stop insects from molting or laying eggs. Ovicides kills eggs. Larvicides kill larvae.
Insecticides also come in several forms: sprays, dusts, baits, and gels. Depending on which form you use and how you use it, the poisons intended for pests can harm pets, people, and the environment.
Insecticides can be repellent or non-repellent. Repellents discourage insects from bothering a plant in the first place. Non-repellents are especially effective against social insects, such as ants. Being a non-repellent, the insecticide is not offensive to the pest, so they walk through it and end up carrying it back to their nest, ultimately killing the entire colony.
Types of insecticides
There are three basic types of insecticide: natural, inorganic, and organic. Natural insecticides are enzymes and other protective substances made by plants as part of their arsenal against insect pests. These natural insecticides include nicotine, neem, and pyrethrum. Pyrethrum is made from the dried flower heads of two chrysanthemum species: Chrysanthemum cinerariifolium and Chrysanthemum coccineum. Other natural insecticides include the chemical that gives horseradish its fiery bite, rosin, and wintergreen.
Inorganic insecticides are made from metals. Organic insecticides are organic chemical compounds that are generally work by making contact with an insect.
The problem with insecticides
Being poisons, insecticides can affect our health, as well as kill insects. Insecticides can also remain in the food supply, increasing in concentration as they move up the food chain. This is important because we are at the top of our food chain. [It is a lot like mercury in fish.] Many of these problems can be reduced or eliminated by understanding the different types of insecticides and using them responsibly.
Like weedkiller sprays, broad-spectrum insecticides are very appealing. A problem appears. You spray it. The problem is gone. Fantastic. Except that the problem is not gone. In fact, the problem just got worse. By spraying broad-spectrum insecticides, all insects are affected. Beneficial predatory insects, pollinators, burrowing soil arthropods, and our beloved honey bees are all subject to the same poisoning.
There are several type of broad-spectrum insecticides, in order of toxicity, all of which interfere with nerve cell transmissions:
Educate yourself about ingredients
Before applying insecticides, you can protect yourself and the environment by learning more about the ingredients. For example, some beneficial insects, such as lacewings, are tolerant of pyrethroids, while beetles, parasitic wasps, and predatory mites are very sensitive to the same chemicals.
You should also ask yourself how long the ingredients of any particular insecticide will remain in the environment. Insecticides are commonly grouped by persistence: short (days), intermediate (up to 6 weeks), or long (months).
Finally, are insects developing a resistance to an insecticide? If so, it should be avoided and another product used.
Reducing risks associated with insecticides
Before resorting to the use of insecticides, be sure you have done the following:
In many cases, it is against federal law to use insecticides improperly, and for good reason.
As quickly as insects can reproduce, it often feels like a losing battle. This is what makes the use of modern insecticides so appealing. Insecticides are an easy way to kill insects. But not all insecticides are safe to use on edible plants. And many insecticides interfere with the delicate balance that exists in a healthy environment. Knowing more about the different ways insecticides work, and how and when to apply them properly, can prevent longterm problems while still reducing the damage done to your plants by insect pests.
When I first read the name drugstore beetle, I conjured up images of an 1800s mercantile being harassed by a gunslinging beetle wearing spurs. I have no idea why.
The truth is, drugstore beetles (Stegobium paniceum), also known as biscuit beetles or bread beetles, are very tiny and don’t look like much of a threat to anyone. Looks can be deceiving.
Drugstore beetles got their name because, until relatively recently, most drugstore pharmaceuticals were made out of dried plants. Drugstore beetles have also been known to feed on chemicals, such as strychnine, once commonly found in drugstores.
Drugstore beetle description
Being brown and covered with microscopic hairs, drugstore beetles look similar to cigarette beetles, but are somewhat larger at 1/8” (3.5mm) in length. Also, where cigarette beetles have smooth bodies and serrated antennae, drugstore beetles have longitudinal grooves along the elytra (wing cases) and antennae that end with three tiny segmented clubs. Drugstore beetle larvae are white grubs with very fine hairs.
Drugstore beetle lifecycle
Female drugstore beetles can lay up to 75 eggs at a time, and the egg-laying season can last for months. That works out to a tremendous number of offspring. Those eggs are usually laid in dried foods, such as cereals, dried fruit, grains, herbs, and nuts. Eggs may also be found in dried meat, hair, wool, and candy.
As those eggs are laid, they are covered with a yeast fungus. This fungi and the beetles cannot live without each other. This is an example of obligatory symbiosis. In less than two months, larvae pupate into adulthood, protected by tiny cocoons, and the cycle begins again.
Damage caused by drugstore beetles
After the eggs hatch, it is the larvae that cause damage by burrowing through and feeding on a wide variety of materials. They also leave frass (big poop) and webbing behind, as well as stray hairs and secretions.
Drugstore beetle larvae love dried plant products, such as cereals, beans, pasta, rice, bread, flour, and spices. Apparently, paprika and chili powder are drugstore beetle favorites, though they will eat practically anything. Larvae are also commonly found in tea, potpourri, tobacco, wreaths, and birds’ nests and they have been known to damage books, leather, hair, and museum specimens.
In the garden, drugstore beetles are a major pest of cumin.
Drugstore beetle control
Drugstore beetles are often carried into the home, garden, or landscape in bulk items, such as grass seed, bird seed, or dry pet food. They may also hitch a ride on packaged food. This is why it is important to look for holes in food packaging and avoid those products. While adult drugstore beetles do not eat, they often chew holes in plastic, foil, and paperboard food packaging. You may also see pockmarks in crackers and pasta. Inspecting foodstuffs and bulk items before you bring them home can prevent infestation.
When bringing crops, such as beans and other seeds, into the home., it is a good idea to freeze them overnight to kill any larvae that may be lurking. This is an easy way to keep your home from becoming infested. Diatomaceous earth (DE) can also be used lightly in areas where drugstore beetles may be lurking.
Pheromone traps and insecticides are not effective against drugstore beetles.
When gooseberry and currant growers find hollowed out, discolored berries that fall off early, it is time to look closely for other signs of invasive gooseberry fruitworms.
Gooseberry fruitworms are the larval stage of the gooseberry moth (Zophodia convolutella). This insignificant looking moth can cause significant damage.
Gooseberry moth description
Adult gooseberry moths are grey with a 1” wingspan. You may be able to see a white fringe on the back of the rear wings, and white horizontal stripes on the forewings, as well as a brown spot. More often, all you will see is a small, narrow-bodied greyish-brown moth.
Larvae are 3/4” long. At first, they are a pale green. As they mature, the head turns brown and dark stripes can be seed down the sides of the body. Sadly, I was unable to track down a photo. Please share one in the Comments if your berries have been so afflicted.
Gooseberry moth lifecycle
Adult moths lay eggs on currants and gooseberries. When the eggs hatch, larvae burrow into the fruit and begin feeding on the pulp. This discolors the fruit and causes it to drop prematurely. A single larva will feed on several berries. Berries may be held together by a silken thread. There is usually only one generation each year but, being invasive insects, the lack of natural predators may cause that to change.
Gooseberry moth controls
Handpick and destroy any larvae you see, or feed them to your chickens. Bacillus thuringiensis and spinosad can also be used against these pests. Treatments should be applied when fruit is first developing and again 10 days later.
Small black spots on tomatoes and tomato leaves often indicate bacterial spot.
Those black spots might not look like anything important, but this bacterial disease can also affect peppers, eggplant, groundcherries, and tomatillos, along with your tomatoes. Close cousin to the bacterial spot of almonds and practically impossible to differentiate from bacterial speck without a microscope, bacterial spot (Xanthomonas campestris pv. vesicatoria ) is perfectly capable of killing your tomato plants.
Bacterial spot symptoms
Symptoms of bacterial spot can appear on all life stages, from seedlings to mature plants, and on all aboveground plant parts. Bacteria enter through wounds and stoma. Infected younger plants can be completed defoliated by bacterial spot. Older plants exhibit insignificant looking water-soaked areas on mature leaves, usually near the bottom of the plant. making it easier to dismiss this disease. This would be a mistake.
Closer inspection of these lesions shows that they start out yellow or light green, turning dark brown or black. Older spots may be raised areas that average 1/3” across. Larger damaged areas may be seen at the margins (leaf edges).
Immature fruit can also be affected by bacterial spot. Bacteria enter through tiny hairs, called trichomes. Infected areas start out looking like tiny raised black dots which then become sunken or dimpled, and surrounded by a white halo, similar to bacterial canker. The halos eventually disappear as the spots get larger and become scabby. These fruits, if they are able to mature at all without rotting on the vine, are still edible. Simply cut out the diseased areas. Just be sure to dispose of the infected parts in the trash. Do not add them to your compost pile.
Controlling bacterial spot
Because these bacteria overwinter in infected plant debris, you can protect next year’s crops by clearing infected plant tissue out of your garden completely each fall. The disease can also appear on volunteer tomato plants, so watch rogue tomato plants closely for signs of infection. Splashing rain, irrigation water, and contaminated tools can also spread the disease, so avoid overhead watering and be sure to sanitize your garden tools regularly.
Since these bacteria need humidity and water droplets to survive, pruning for good air flow can go a long way toward preventing this disease.
If you are like me and save seeds from each year’s crops, be sure you don’t use seeds from an infected plant, as you will be perpetuating the disease. As always, only buy certified disease-free plants and seeds and always quarantine new plants. Fixed copper sprays can be used in areas where bacterial spot has been a significant problem, although there have been some cases of copper-resistant bacteria. Crop rotation can also be used to break this disease triangle.
Protect next year’s crops by tossing plants infected with bacterial spot into the trash and providing good air flow around future plants.
If you grow raspberries, you should be on the lookout for spur blight. For some reason, blackberries and other bramble fruit are not affected by the Didymella applanata fungi. Red raspberries are more likely to become infected by this fungal disease than other raspberry species, but all raspberries can get spur blight.
Currently found most often in Scotland, Oregon, and Washington, spur blight can significantly reduce your raspberry crop. Knowing what to look for can help you nip this disease in the proverbial bud.
Spur blight symptoms
Spur blight first appears in mid to late summer on new growth, on leaves and around buds. Initial symptoms of spur blight look a lot like anthracnose, fireblight, and cane blight, with brown and purple lesions on leaves, around buds, and on the lower area of stems. These lesions cause buds to shrivel up. By spring, those lesions will look ashy grey and the buds will be weak or dead. Stems that grow from these infected buds will be wilted and weak.
Infected leaflets have triangular-shaped brown areas and they may fall off, leaving the petiole (leaf stem) in place. You might also see dead spots on the canes near petioles. This infection causes premature leaf drop, which weakens the plant overall. As the blight progresses, splits and cracks may form in the bark.
If you look closely, you might see tiny black dots emerging from those cracks. Those dots are fungal fruiting bodies, called pycnidia. If you look at pycnidia with a microscope, they are flask-shaped. Pycnidia formation is followed by a different type of fruiting body, called perithecia. Perithecia are also black, but they are medium-sized and, if you watch, erupting with spores.
Spur blight lifecycle
Spur blight is spread by spores on wind, rain, and irrigation water. These spores are released each time wet weather occurs, even if that wet weather is your garden hose. If that infected water falls on or near young canes, newly forming buds, leaves, wounds, or stoma, infection can occur. Once inside, this disease spreads throughout the plant, overwintering in the lesions.
How to manage spur blight
Proper sanitation and pruning methods will go a long way toward preventing spur blight on your beloved raspberries. In late winter or early spring, before new canes emerge, remove all dead, diseased, or weak canes and put them in the trash, rather than the compost pile. Be sure to keep canes properly spaced for good air flow, and train them up trellising that allows canes to dry quickly and to make it easier for you to water your raspberry plants at ground level. You should also keep weeds away, as they complete for water and nutrients and reduce air flow around the canes. Unless a soil test has indicated a genuine need for fertilizer, avoid feeding your raspberries. The presence of too many nutrients causes plants to produce an abundance of vulnerable tissue.
As always, only buy certified, disease-free plants and place new plants in quarantine. In the case if severe infection, fixed copper or lime sulfur treatments may reduce lesion size and control internal infection if applied when new shoots are 8-10” long.
Believe me when I tell you that it is far easier to prevent spur blight than to treat it. And raspberries are worth the effort.
Strawberry vein banding is a viral disease spread by strawberry aphids, but you will never know it has infected your plants until another virus comes along.
As soon as another virus infects your plants, usually strawberry crinkle, suddenly the leaf veins of your strawberry plants start to turn yellow. And if the strawberry mottle virus comes along, well, those yellowing veins won’t be visible. This mess is called strawberry decline, a topic for another day.
Symptoms of strawberry vein banding
Leaves of infected plants tend to be significantly smaller than the leaves of healthy plants. The yellowing of veins, when visible, first appear in new growth. This yellowing appears erratically; sometimes only part of a vein has turned yellow. The two halves of each leaf may be held closer together than is normal and the margins, or leaf edges, are wavier than normal. Some crinkling of the leaf surface may also occur. As the leaf opens, the bands of yellow become somewhat more obvious.
Symptoms appear more strongly in the second and third leaves, but are not likely in later growth. [Weird, right?] Unfortunately, the other symptoms include stunting and reduced fruit and runner production. Your strawberry crop can be reduced by nearly 20% because of vein banding. As soon as another virus takes hold, you can lose your crop entirely.
Strawberry vein banding vectors
Strawberry vein banding is generally carried by strawberry aphids. It can also be transmitted by taking grafts from infected plants. Strangely enough, coming into contact with dodder can also spread the disease, but sap from an infected plant cannot. Stranger still, a clone of the vein banding virus can infect turnips, a completely unrelated species.
Strawberry vein banding control
In a word, you can’t. Strawberry vein banding can be prevented by only installing certified disease-free plants, placing those plants in quarantine when they first arrive, and removing any plants that you suspect are infected.
Since aphids can fly at certain points in their development, the threat of this and other viruses is constant. All you can do, besides the preventive measures listed above, is monitor your plants for signs of aphids and control them as well as you can. Insecticides and insecticidal soaps work against aphids, but your strawberry plants need honey bees and other pollinators to produce fruit. Those insecticidal controls will impact your helpers, too, so they should be avoided while plants are flowering.
Closely monitoring your strawberry plants and keeping other plants that might host aphids at a distance can go a long way toward preventing vein banding in your strawberry plants.
Strawberry pallidosis is one of several viruses that make up a condition called virus decline.
Infected with only one of these diseases, strawberry plants often remain symptomless. It isn’t until a second virus enters the game that symptoms begin to appear. These other viral diseases include strawberry vein banding, crinkle, mottle, mild yellow edge, and beet pseudo yellows.
Symptoms of strawberry pallidosis
Similar to other strawberry viral diseases, symptoms of strawberry pallidosis include stunting, significantly reduced fruit and runner production, and older leaves turning red or purple. An additional symptom of strawberry pallidosis is that roots are brittle and show fewer rootlets.
Managing strawberry pallidosis
Unlike many other strawberry viral diseases, pallidosis is spread by whiteflies. This makes controlling the disease more difficult. Management strategies are the same for all strawberry viral diseases: only install certified disease-free plants, quarantine new plants, remove infected plants, and control whiteflies as much as you can.
Strawberry mottle is an unassuming viral disease that can cut your strawberry crop by 30%.
Strawberry mottle is one of several viruses that can affect strawberries. Appearing on its own, the damage tends to be relatively isolated. All too often, however, more than one virus appears at the same time. Collectively, this condition is called virus decline and it can eliminate any chance at enjoying a sweet, juicy strawberry from your garden, no matter how well you care for your plants.
Vectors of strawberry mottle disease
Strawberry mottle is carried by insects, most commonly by strawberry, melon, and cotton aphids. This virus is also spread by vegetative propagation of infected plants. Unlike the strawberry mild yellow edge virus, which is retained in an aphid’s gut for its lifetime, the strawberry mottle virus can only be transmitted for 2 or 3 hours after an aphid or other insect has fed on an infected plant. This makes outbreaks remain relatively localized. [Ten feet away probably looks impossible to a flightless bug that is only 1/8” long.]
Symptoms of strawberry mottle
As insects pierce plant cells to suck out the sugary sap, viruses move from the insect’s saliva to the plant. As viruses tend to do, these pseudo-lifeforms start reprogramming a plant’s cells to produce more viruses, which then clog the works.
Strawberry mottle first appears on young leaves as smaller than normal leaves that may also show yellow distorted areas. Plants may be stunted and they certainly produce less fruit and runners than they might otherwise. As the disease progresses, symptoms become more severe, with older leaves turning red.
Strawberry mottle management
Strawberry mottle is more likely when plants are left in place over the winter, but that doesn’t mean you have to rip out your plants every year. [Note: don’t actually rip plants out of the ground. Instead, cut them off at soil level to leave valuable soil microbes in place.]
As always, to reduce the likelihood of strawberry mottle appearing in your garden, only buy certified disease-free plants and always place new plants in quarantine. As much as possible, try to control aphids around strawberry plants. If a plant becomes infected, remove it.
For some reason, strawberry plants tend to get infected with more than one virus at the same time. Strawberry mild yellow edge virus is one of those diseases
Strawberry mild yellow edge virus is a long name for a disease that can reduce your strawberry crop by as much as 30%. Strawberry mild yellow edge virus often appears at the same time as the mottle virus, both of which are transmitted by some aphid species. Nematodes may also add raspberry ringspot virus to the mix.
Strawberry mild yellow edge virus symptoms
As with most viral diseases, stunting is a common symptom of strawberry mild yellow edge virus. Older leaves may turn bright red, but leaves around the crown nearly always exhibit yellow margins or edges, hence the name. These yellowed areas eventually die and turn brown. Leaf cupping may also occur.
Since these symptoms look a lot like water-stress, fertilizer burn, overly acidic pH, boron toxicity, or bad weather, it is important to rule those things out before deciding on a plan. Once strawberry mild yellow edge virus has made an appearance in your garden, there are steps you can take to minimize the damage.
How to manage strawberry mild yellow edge virus
Even though the fruits of infected plants are still edible, plants infected with strawberry mild yellow edge virus should be removed to reduce the chance of spread. Aphids carrying the strawberry mild yellow edge virus are disease vectors for life. The only thing to do if the disease is present is to use insecticidal soap on each and every aphid that might be a carrier. Just be sure to do this at a time when honey bees and other pollinators will not be attending the flowers. Common lambsquarters and other Chenopods can also carry this disease, so keep these plants away from your strawberry plants.
This disease is most common when plants are grown using a matted-row method. The matted-row system allows parent plants to send out runners, or daughter plants, which will produce fruit the following spring. This is a very productive method that has been around for a long time. It gets its name because the runners end up intertwined, creating a mat. The only problem with the matted-row system is that it means plants are in place for a longer period of time. This makes infection more likely.
As always, place new plants into quarantine until you are sure that they are disease-free.
Strawberry crinkle might sound like a delicious new candy bar, but it is one of the most destructive viral diseases a strawberry plant can face.
Strawberry crinkle virus was first seen in Oregon and California in 1932 and is now found worldwide. Spread by aphids, this disease is commonly seen in tandem with other aphid-transmitted diseases, such as mottle, mild yellow edge, pallidosis, and strawberry vein banding. As aphids feed, their saliva transfers the virus to every plant they visit.
Strawberry crinkle virus symptoms
Wilting, reduced runner production, smaller fruit, deformed and/or streaked flower petals, and crinkled leaves are all symptoms of strawberry crinkle virus. Vein spotting may also be seen, as well as lesions on petioles (leaf stems) and stolons. Infected plants may appear top-heavy, exhibiting a form of epinasty. These symptoms can vary in intensity.
Strawberry crinkle virus management
Since bees are so important to strawberry formation, insecticides are generally not an option against the aphids that carry this disease. Use these tips to prevent strawberry crinkle virus from impacting your strawberry crop:
Hopefully, your strawberry plants will never become infected with the crinkle virus. Until we figure out a sustainable way to get rid of aphids, well, be on the lookout.
Avocado lace bugs, also known as camphor lace bugs, can cause problems on avocado, red bay, and camphor trees, along with azaleas and rhododendrons.
Native to Florida, Texas, the Caribbean, French Guyana in South America, and eastern coastal Mexico, avocado lace bugs (Pseudacysta perseae) are not a serious problem when found in small numbers. Or where they have no natural predators.
Avocado lace bug description
Avocado lace bugs get their name because of the lacy venation of their wings, but the way they protect themselves with a lacy cover as they hide on the underside of leaves but be another good reason. That cover is actually the avocado lace bug’s thorax and forewings.
Avocado lace bugs are only 1/16” to 1/12” long, brown, orangish, or black and oval-shaped. They tend to cluster together, creating what looks more like a messy fungal growth than an insect colony. If you look closely, with a hand lens, you would see that avocado lace bugs have a black or brown head or thorax, with white, orange, or brown legs, wing covers, antennae, and abdomen.
Avocado lace bug nymphs are dark and spiky, with pale legs and antennae. Eggs look like sprinkled black pepper even though they are actually oblong and yellow. The black color comes from the fact that these tiny oblong eggs are smeared with what looks like poop.
Avocado lace bug lifecycle
Yes. That’s what I said. Poop. Female avocado lace bugs lay their eggs and then smear the area with a sticky, tar-like substance that looks like poop. Under that protective layer, nymphs molt 5 times as they grow before emerging as adults. Avocado lace bugs have several generations each year and all developmental stages can be present at any one time.
Avocado lace bug damage
Avocado lace bugs are sap suckers. As such, they pierce the underside of leaves and siphon away nutrient rich fluids. This feeding, while trivial in small numbers, can cause stippling. As feeding progresses, other symptoms appear, such as leaf tip burn that looks like salt damage, leaf discoloration, and early leaf drop. Large infestations can result in defoliation, sunburn damage, and reduced fruit production.
As in any case where plant cells are pierced, this feeding also provides points of entry for fungal diseases, such as anthracnose.
Avocado lace bug control
Natural predators should keep avocado lace bug populations in check. These beneficial insects include jumping spiders, lacewing larvae, lady beetles, and predatory mites and thrips, as well as parasitic wasps.
If avocado lace bug populations reach troublesome numbers, keep your trees healthy with a thick layer of mulch, good drainage, and regular irrigation. Insecticidal soaps are somewhat helpful against avocado lace bugs.
Be on the lookout for this pest. If you suspect your tree is hosting avocado lace bugs, contact your local County Extension Office right away. As always, place new plants and bare root trees in quarantine before adding them to your garden.
You can grow a surprising amount of food in your own yard. Ask me how!