Have your new seedlings been chewed off at ground level? It may be darkling beetles.
Darkling beetle is the common name for all 20,000 species within the Tenebrionidae family. Some of the more famous California darklings include Blapstinus, Coelus., and Eleodes..
Darkling beetle identification
Darkling beetles are dull black, blueish-black, or rusty brown, depending on the species. Unlike other beetles, the wings of darkling beetles are fused together. Some species have longitudinal ridges on their wing covers, but most are smooth, without markings of any kind. One exception is the wooly darkling beetle (Eleodes osculans), which is covered with tiny hairs. Darkling beetles can range from 1/8 to 1-1/2 of an inch long. The antennae are well developed and often have knobs at the ends (clubbed).
Darkling beetles are frequently confused with predaceous ground beetles (Carabidae), but ground beetles are shiny and their antennae are more delicate. There are other differences, but you get the idea. Darkling beetle larva look like pale yellow or dark brown wireworms. They are less than 1/3 of an inch long and are often called false wireworms. You may know one particular branch of this family as mealworms (Tenebrio molitor).
Did you know that mealworms can digest styrofoam?
Stanford researcher Craig Criddle discovered that the bacteria found in a mealworm’s gut can transform polystyrene into “carbon dioxide and recyclable organic waste.” How cool is that?!!? (UCANR)
Darkling beetle behavior
These pests tend to walk with their heads down and their abdomens somewhat lifted. Very often, they will stand completely still, in a headstand position, if frightened. While not dangerous, they can squirt you with a nasty smelling secretion from that rear end that does not wash off easily. This behavior is what gives some darkling beetles the name Skunk Beetle or Stink Beetle, not to be mistaken with stinkbugs. For the most part, these pests only come out at night, but you may catch one running across the patio or lawn during daylight hours. Normally, they hide under dirt clods, fallen tree bark, rocks, boards, wood chips, and in other dark places during the day. Often, the only way you know you have a darkling beetle problem is because of the damage they cause.
Darkling beetle damage
In addition to attacking seedlings at ground level, darkling beetles feed on the foliage of many garden plants, such as lettuce, chicory, cabbage, broccoli, and other brassicas, beans, melons, pumpkins, tomatoes, and squash. This feeding can be seen along leaf edges and on the underside of leaves. Darkling beetles also feed on the ‘netting’ (raised areas) of melons, the flowers of most cucurbits and pistachio, and on some fruit crops, such as figs.
Some species of darkling beetle also act as vectors for plant diseases and poultry parasites. Some darklings can also cause structural damage to insulation and wooden buildings. They are also attracted to poultry feed, but my guess is that the chickens make short work of that arrangement, as long as the unavailable feed is stored properly, in a metal container.
Darkling beetle control
Commercial farmers use insecticides to kill these pests. They also use a shallow ditch, filled with water, to block these pests from coming out of the weeds and into the fields. If you are an organic grower, as I am, you will have to use cultural controls. You can minimize darkling beetle damage organically when you:
In 2015, a report published by The Coleopterists Bulletin warned that three non-native darkling beetles have been found in California and Nevada. Each of these species is somehow tied to ant or fire ant populations:
I was unable to find any freely available photos, so you will have to track them down on your own. If you see any of these invasive beetles, please capture them and contact your local County Extension Office.
You may be surprised to learn that some people keep darkling beetles as pets.
If you have citrus trees, you probably have citrus mealybugs.
Cousin to scale insects, these tiny pests are often overlooked. At first, all you may see is some sooty mold on a few leaves, an ant trail, marching up and down the trunk of the tree, or, finally, the telltale cluster of fuzzy white, tucked under leaves or in crevices. Left unchecked, mealybugs can scar fruit, and cause chlorosis (yellowing), early leaf and fruit drop, and poor overall tree health.
Citrus mealybug varieties
There are actually four different mealybugs that attack citrus in the Bay Area:
Citrus mealybug description
All mealybugs are soft, flat, oval-shaped critters with segmented bodies. The mealybugs that attack citrus are covered with a white wax that also creates spines (filaments) around the outer edge and the back end. Unless you use a hand lens, you probably won’t notice individuals, but mealybugs colonize areas, creating white, fuzzy egg clusters that are easy to spot.
Male citrus mealybugs are not needed for reproduction, but they are needed by long-tailed mealybugs. When mealybug eggs hatch, the 'crawlers' are pale yellow, with red eyes, and distinct antennae. Crawlers are not born with their protective wax coating. They begin to excrete it soon after hatching. They are called crawlers because they crawl to a feeding site, where they will continue to develop (and damage fruit) for a month or two.
Citrus mealybug damage
Each female mealybug can lay hundreds of eggs, and there are usually two or three generations a year, so infestations can become a problem. As sapsuckers, citrus mealybugs pierce fruit, leaves, and young stems, to get at the sap. They also feed on tender, new growth. As they feed, they leave behind a trail of honeydew that attracts protective ants, and creates the perfect growth medium for sooty mold. Citrus mealybug feeding near fruit stems also leads to fruit drop. Citrus mealybug feeding also reduces fruit quality. Trees fail to thrive and are prone to infestation by disease and other pests. In addition to oranges, lemons, limes, and grapefruit, citrus mealybugs also have a taste for ornamental plants, such as tulips, coleus, cyclamen, begonias, and dahlias.
How to control citrus mealybugs
The first step to controlling citrus mealybugs is to monitor your trees, especially in spring and fall, for signs of ant trails, sooty mold, and egg clusters. Since ants will protect and farm the aphids for their honeydew, apply sticky barriers to tree trunks to block ants from protecting the aphids against their natural predators. Those natural predators are your trees’ best defense against citrus mealybugs. Ladybugs, lacewings, and hoverflies will devour these pests, so avoid using broad-spectrum pesticides. For extreme infestations, you can buy an introduced predator, called the mealybug destroyer (Cryptolaemus montrouzieri). Insecticides are not recommended. Diatomaceous earth and insecticidal soaps can be used.
Mealybugs prefer dusty conditions, so hosing trees off can make them less appealing to citrus mealybugs.
Warm winter days and glossy seed catalogs lure many novice gardeners into starting seeds too soon.
Okay, it’s true. Veteran gardeners are vulnerable to the same overly idealistic behavior. Most of us, however, have learned that starting seeds too early nearly always leads to damping off disease and seed rot. And it’s a waste of good seed, since both conditions are nearly always fatal. If the plant isn’t killed outright, it will always be stunted and fail to thrive.
What causes seed rot?
Cold and wet are a recipe for disaster for most seeds. Seed rot occurs when seeds are placed in soil when temperatures are too low and moisture levels are too high. The moisture softens the tough outer seed coat, allowing fungi, such as Achlya plebsiana, Fusarium, Pythium, and Rhizoctonia to enter. These are not the beneficial mycorrhizae that help your plants find food. These fungi are out for blood. Okay, not blood, but they will suck the life out of your seeds and seedlings.
Seed rot symptoms
Planted too soon, seeds may plump up and then turn to mush. They will often develop a white, fuzzy growth. This growth is one of the aforementioned fungi. The fungi form a halo around the seed, and work their way inside. If that weren’t bad enough, within just a few days, several different algae will begin to colonize the fungal growth, turning it green. In both cases, the seed is being sapped of the strength it needs to grow.
Locked inside a healthy seed, safe under a hard shell (seed coat), the embryo and a store of starches (endosperm) wait for conditions to be Just Right. Once specific levels of heat, light, air, and moisture are present, enzymes within the seed are activated. These enzymes convert the endosperm into usable sugars and the embryo can begin to germinate. If conditions are not correct enough, the young plant will be at a disadvantage that can be fatal.
How warm is warm enough?
The minimum soil temperature for many common garden plants is listed below. Soil temperature is taken two inches below the surface, where many of the roots will be found. Keep in mind, the optimum temperature for germination is often 20°F to 40°F higher:
Until your last frost date has passed (It’s March 15, in my area.), the only way to safely start seeds any earlier is indoors or in a greenhouse, under grow lights, and on a seed mat that provides steady, controllable heat. [Do not use the same heating pad you use on your aching back - it is not designed for moisture and it will get too hot and can become a fire hazard.]
Preventing seed rot
While fungicides are frequently used in commercial farms to prevent seed rot, good cultural practices in the home garden can be enough to prevent this problem. Simply follow these three tips and your seeds should be fine:
As tempting as it may be to start earlier, waiting until conditions are suitable is one of the simplest ways to ensure a good harvest.
Diamondback moths are common pests of cole crops.
Cole crops include broccoli, Brussels sprouts, cabbage, cauliflower, and Napa cabbage. That’s where I saw the damage. My Napa cabbage was growing very nicely, enjoying our cool winter weather, but the leaves looked more like Swiss cheese. That’s because diamondback caterpillars prefer older leaves, so the first sign of infestation you will see is a bunch of holes in the larger leaves. They also feed on flower buds and flower stems.
Diamondback moth lifecycle
Adult diamondback moths lay their eggs on the underside of leaves and they are very difficult to see. When the eggs hatch, tiny caterpillars burrow their way into the crown for safety. When a diamondback moth caterpillar is disturbed, it will jump ship, rappelling away from danger using a thin silken thread to swing to safety. After feeding for a couple of weeks, diamondback moth caterpillars spin a loose cocoon on nearby leaves or stems, where they pupate.
Diamondback moth control
Personally, I have caught a few diamondback moths on good old fashioned fly paper strips. That isn’t a very effective control method however. Maintaining biodiversity in your garden is one way to attract the ichneumonid wasp, a predator of diamondback moth caterpillars. Spraying Bacillus thuringiensis and spinosad are effective organic control methods.
Aphids, or plant lice, are nearly always a problem, here in the Bay Area. This is particularly true when it comes to cabbage aphids.
Cabbage aphids (Brevicoryne brassicae) can wipe out a cabbage crop before it ever gets started. Native to Europe, this pest of cole crops is now found throughout the United States.
Vulnerable young cabbages
Cabbage aphids feed on the youngest, most tender parts of new cabbage, broccoli, Brussels sprouts, kale, and cauliflower. These pests love to feed on the innermost parts of cabbage and Brussels sprouts heads. Large colonies can stunt or even kill young plants. Heavy aphid feeding causes leaves to curl up, providing the pests with even more protection.
Controlling cabbage aphids
Prevention is key to cabbage aphid control. My cauliflower plants, which had been protected under row covers, were left untouched, while my cabbages and broccoli were hit hard. Once aphids are seen, you can often use a strong spray from the garden hose to dislodge them. If that doesn’t work, insecticidal soaps can provide some control. Since soap may be phytotoxic, especially on cabbage and Brussels sprouts, it is a good idea to apply them on a foggy day. Also, remove any weeds in the mustard family from the area. Cabbage aphids can hide out in the mustard and then return to your garden. Pesticides can be used, as a last ditch effort, but aphids are developing resistance to these chemicals and that can be a dangerous spiral.
Another problem with using pesticides against cabbage aphids is that those same chemicals also kill beneficial, predator insects, such as lady beetles, parasitic wasps, and the syrphid fly (hoverflies). These helpful insects are natural predators of caterpillars, imported cabbageworms, diamondback moths, loopers, and armyworms, which can cause other problems for your cole crops.
Monitor your plants every couple of days and be on the lookout for cabbage aphids!
The letters V, F, and N on a seed packet or plant label refer to certain types of disease resistance and pest tolerance.
All of us work to make our plants healthier. At the end of a growing season, many of us save seeds from the very best fruits and plants for next year. [If you’ve never done this before, I urge you to give it a try. I’ll write about seed saving tomorrow.] By saving and planting seeds from the best plants each year, we are choosing specimens that are better suited to our microclimate and personal tastes.
Building better plants
When we save and plant seeds from specific plants, we are cultivating certain characteristics. A more intensive method of building better plants is to purposefully pollinate one plant with the pollen of another. Taken to the far end of this spectrum, we have plants that are genetically modified in the lab. [I used to be bothered by this, until I learned that plants have been doing it to each other for a very long time. See Dodder.] These manipulations are often used to encourage certain characteristics such as color, flavor, days to maturity, disease resistance, or pest tolerance.
Disease resistance and pest tolerance
Some plants are susceptible to certain diseases, while others are not. The same is true for pest infestations. In both cases, you can generally use the disease triangle to reduce the impact pests and diseases have on your garden. The disease triangle consists of the environment, the plant, and the problem. Change one of those three and the problem can be reduced or eliminated. Installing plants that are already resistant to some of your garden’s more common problems can reduce your work load and keep your plants healthier. That’s where V, F, and N come in.
V is for verticillium wilt
The V tells you that a particular plant is resistant to verticillium wilt. Verticillium wilt is a soil-borne fungus that attacks tomatoes, peppers, berries, snapdragon, eggplant, potatoes, and over 300 other garden varieties. Plants infected with verticillium wilt exhibit chlorosis, wilting, and leaf drop as the fungi breed, blocking the flow of water and nutrients through vascular tissue. Verticillium wilt fungi can stay in the soil for several years, so infected plants should be thrown in the trash. If you have a garden patch affected by verticillium wilt, use crop rotation and plant non-host species, such as beans and other legumes, broccoli, corn, and cereal grains. Non-host species are not affected by this disease.
F is for fusarium wilt
Fusarium wilt is another soil-borne fungal disease. As these fungi (Fusarium oxysporum) reproduce, they cause bleaching, chlorosis, stunting, damping-off, and brown veins. Fusarium wilt frequently attacks peas, beans, and other legumes, tomatoes, tobacco, sweet potatoes, cucumber and other cucurbits and even banana plants. There are actually several different strains of Fusarium wilt, so you may see F, FF, or FFF, depending on which strain the plant is resistant towards. [Check with your local County Extension Office to learn which strain is in your area.]
N is for nematodes
There are good nematodes and there are bad nematodes. Bad nematodes feed on the roots of several different garden plants and fruit trees. Aboveground symptoms include afternoon wilting, chlorosis, and a general lack of vigor. To verify a nematode problem, you have to dig the plant up. Nematode feeding causes swollen areas called galls, on the roots. Roots will also look stunted and deformed.
Seeing V, F, and N is not a guarantee. It simply tells you that a particular variety of plant is resistant. Sometimes, that little extra resistance can make all the difference.
Cavity spot is not your worst prison nightmare, instead, it is a fungal disease of carrots.
Cavity spot appears as depressed lesions on mature carrot taproots. These lessons can be elliptical or irregular in shape. They start out quite small, as sunken pinpoints that grow larger as the root grows. Lesions are usually less than 1/2 inch across, but they can get much larger. These lesions are usually seen on the top one-third of the carrot, near where lateral roots emerge.
This fungal disease is caused by Pythium sulcatum and P. violae spores found in the soil. These spores become active in cool, wet weather. The same time your carrots are growing. Cavity spots occurs most often when soil temperatures are near 58°F. In addition to carrots, cavity spot occurs on alfalfa, beets, blackeyed peas, celery, cucumber, wheat, and several weeds.
Controlling cavity spot
Harvesting carrots as soon as they are mature will reduce the chance of them becoming infected. And avoid over-watering. Too much moisture in the soil encourages several different fungal growths. A three-year crop rotation is the best way to prevent this disease, or to interrupt the disease triangle in your garden.
So, protect your carrot crop with good cultural practices and just the right amount of irrigation!
The Mediterranean fruit fly has reappeared in California!
Periodically, in the world of gardening and agriculture, a cry goes out across the fields, farms, and front porches of California, and the world, announcing that a medfly has been found. This time, a medfly has been found in Half Moon Bay
Native to sub-Saharan Africa, medflies (Ceratitis capitata) have slowly been making their way around the globe, usually riding on fruit and other infested crops. Medflies are about 1/4” long. They have a black thorax, marked with silver, and a tan abdomen with dark stripes. The wings are clear, with two light brown bands and gray flecks at the base. Their eggs look like those of other fruit flies: they look like tiny white bananas. Larvae are white, legless, and pointed at the back end. Pupae are encased in a hard, shiny brown puparium.
Damage caused by medflies
Medflies lay their eggs in the skins of over 250 different fruit, nut, and vegetable crops. When the eggs hatch three days later, the maggots burrow into what we normally eat, making it inedible. Once maggots have eaten their fill, either the rotting fruit falls, or they drop to the ground where they pupate in the soil. In one week, an adult emerges and the whole cycle begins again.
Crops affected by the medfly
It would probably be easier to list the crops not affected by medflies, but this should give you an idea: apples, apricots, avocados, cherries, figs, grapes, grapefruit, lemons, limes, melons, nectarines, oranges, peaches, pears, persimmons, plums, pomegranates, sweet peppers, tangerines, tomatoes, and walnut.
The ripple effect
Like most things in life, this situation is not limited to bug-infested food plants. Commercial and home growers will end up using more pesticides to counteract this insect, which can lead to more ground water contamination and chemical resistant pests. Also, areas with medfly populations are unable to sell their produce, infested or not, to other states and other countries. Finally, native plants that produce fruit or nuts can also be attacked by this pest.
The first appearance of a medfly in California took place in 1975. I remember hearing about it in the news - everyone was talking about it. The government declared a “state of emergency” and 100 square miles were placed under quarantine, and 600 million sterile male medflies were released, to interrupt breeding. Malathion was sprayed all over the place. It cost $1 million and took a year, but the medfly was eradicated. For a time.
When the medfly returned in 1981, Governor Brown delayed aerial spraying of malathion, claiming environmental concerns. That was when we learned that medflies reproduce and feed at astounding rates. In that case, the medflies needed only one month to destroy millions of dollars of crops, and to threaten billions more, over an area of 530 square miles. When it was realized just how devastating this pest could be, the California National Guard was called upon to create highway checkpoints to confiscate infested produce.
Now, when a single medfly is spotted, it is checked for gender and fertility, and then all the stops are pulled: aerial spraying, ground spraying, trapping, irradiation, releasing sterile male medflies, public information, and quarantines. Since 1985, medflies have been found in California in 2007 (Dixon), 2008 (El Cajon), and now in 2017. Currently, there are two active medfly quarantines in California: Fairfield (Solano Co., just north of Contra Costa) and Sun Valley (Los Angeles Co.). The Half Moon Bay infestation brings that number to three.
What can you do?
First, never, ever, EVER smuggle fresh produce, plants, or soil from infested areas into California. Don’t mail fresh produce into uninfested areas either. For more information, contact the California state Dept. of Food and Agriculture at (650) 363-4700.
IF YOU THINK YOU SEE EVEN ONE MEDFLY, PLEASE REPORT IT!
Robber flies assassinate their prey in the air, injecting them with paralyzing neurotoxins and enzymes that liquify their preys’ insides. Also known as assassin flies, robber flies (Asilidae) aggressively hunt other insects. They often look more like bees or dragonflies to the casual observer. And they are in your garden, for better or worse.
Robber fly description
There are over 7,500 different species of robber fly, ranging in size from 0.2 inches up to 2 inches long. All of them are sturdy, bristled flies with a distinct mustache, made of of bristles (setae), called a mystax. Robber flies, like many other insects, have three simple eyes (ocelli), in a depression on top of their head, between two very large compound eyes. [Simple eyes, like ours, have only one lens, while compound eyes have many lenses.] Robber flies generally have robust legs with spines, and short, segmented antennae. Most species of robber fly have long, skinny bodies with stinger-like ovipositors, while others look more like bumblebees. Robber flies will inflict a painful bite with their proboscis (tubular mouth part), if they feel threatened.
Robber fly life cycle
There is surprisingly little known about the private lives of robber flies. They seem to prefer dry, sunny, open environments. Each robber fly can live for up to 3 years. Eggs can be translucent (hyaline) or pigmented, spherical or oval, depending on the species. Yellowish or white larvae, with tapered bodies and a dark head, are believed to live in leaf mold, rotting wood, and in the soil. There are four larval stages, or instars. Scientists are only now learning about the feeding behavior of robber fly larvae. It’s pretty strange. For one thing, the first instar does not eat insects; it probably eats dead things. The second instar eats beetle larva secretions. [Don't ask.] Later instars are actual predators. Robber fly pupa are naked and have leg stubs, so they can move around, similar to hornworm larvae.
Robber fly prey
Robber flies are generalists. That means they will chase after and kill pretty much anything that flies by, beneficial or not. That is why I said, for better or worse.” Robber flies will kill many garden pests, but they will also kill beneficial insects. Some of these prey insects are pretty substantial in size, compared to a robber fly. But, adult robber flies are excellent fliers. You can usually hear them coming, but for their prey, it’s already too late. Hiding in ambush, a robber fly spots its target, gives chase, and grabs ahold with its tarsi (front legs) before injecting a chemical cocktail that paralyzes the prey and liquifies its insides. The most common victims of robber fly attack include:
They have also been recorded feeding on:
And, hummingbirds. It’s rare, but it has happened. You can see some excellent video of robber fly behavior at Mike Blair Outdoors.
Have you seen any robber flies in your garden? Do you consider them to be Good Guys or Bad Guys?
Ringspot, or black blight, is a fungal disease of Brussels sprouts.
If you have opted to grow Brussels sprouts, your are in good company. Brussels sprouts, fresh from the garden, look like an impressive Medieval weapon and taste far sweeter than the frozen, store-bought variety. [Show up at Grandma’s house on Thanksgiving with a freshly cut stalk of Brussels sprouts and I can guarantee you will be the talk of the day!]
Impressive and delicious, your Brussels sprouts plant may develop light brown or black leaf spots, often with a yellow halo. The spots are usually limited by leaf veins and can have an angular shape. These leaf spots are fungal population explosions. In severe cases, these lesions can also occur on the sprouts. Over time, the spots begin to look more like the concentric rings of a target. If you look closely, with a hand lens, or using a microscope, you can actually see the fruiting structures. Complete leaf loss can occur.
Ringspot life cycle
Since the infected leaf is going to be lost anyway, remove it and throw it in the trash. The pathogen that causes black blight, Mycosphaerella brassiciola, is already in the soil, and it travels on the wind and via splashing rain. It prefers the cool, moist conditions that commonly occur in California autumns - just as your Brussels sprouts are really growing. In other regions, this disease commonly infects broccoli, cabbage, cauliflower, and weeds in the brassica family, such as mustard. It generally only causes significant problems in the Bay Area on Brussels sprouts. I don’t know why.
Since the pathogen is probably in your soil, the best control measure is to plant resistant varieties. Also, monitor plants for signs of black blight. Infected plants, or plant parts, should not be added to compost. If ringspot has occurred in your garden, try a 2 to 3 year crop rotation and remove weeds that may host the disease.
A small swarm of tiny flies goes airborne when you grab a banana and it seems like you can never quite get rid of them. What are these tiny pests and how can they impact your garden?
Let me start by saying that there is far more to these fruit flies than meets the eye. What started out as a simple post about a common garden/household pest has led me down rabbit holes I never knew existed.
First, fruit flies do not actually eat fruit. Instead, they are attracted to overripe, fermenting fruit, where they can find the yeast bacteria that they do eat. Like other fly species, they lay eggs near favorite foods, which then hatch into larva, or maggots. While fruit flies will not hurt you, they are not something you want in your food, or your garden. Let’s find out why.
Fruit fly life cycle
These tiny pests often take a ride into your home on store bought produce, usually as eggs or pupae. Fruit flies thrive when there is humidity and temperatures of 80° to 89°F, much like the inside of your kitchen. Anything above 105°F will kill fruit flies in a matter minutes and cold temperatures have a similar effect. In spring or fall, however, a single female fruit fly may lay up to 700 eggs in her 25- to 30-day life. What’s worse, when she lays an egg, she coats it with her feces (poop)! This transfers a beneficial bacteria to future generations. These poop-covered offspring hatch 12 to 15 hours later and feed for a few days on your kitchen or garden produce, molting twice in the process. Once these maggots have eaten their fill, they enter a pupal stage that lasts only a few days. This means that each egg becomes a sexually mature fruit fly in about a week!
Fruit fly description
There are actually thousands of different fruit fly species around the world. Most of them are less than 0.12 inches long, brown or yellow, with red eyes. The legless maggots are yellowish-white, only 0.2 inches long, and some species have pointed ends. Pupae are oblong with a forked breathing tube at one end. Some insects, such as Malaysian fruit flies (Bactrocera latifrons) are actually blowflies, and not true fruit flies. There are two major families of fruit fly: Drosophila and Tephritidae.
Because of their short lifecycle and profound reproduction rates, Drosophila, also known as vinegar flies or common fruit flies, are very popular in genetic research laboratories. The common fruit fly genome is well documented, with only four pairs of chromosomes. The most common species in California are D. melanogaster and D. simulans. Only one of the common fruit fly’s claims to fame includes the fact that their sperm cells are 2.4 inches long, which is 20 time longer than the fly, and 1,000 times longer than human sperm cells. I don’t know how they do it.
The Tephritidae family are sometimes referred to as peacock flies, due to their colorful markings. These markings often mimic other, actually dangerous insects. This copy-cat behavior is called Batesian mimicry, in case you were curious. There are over 5,000 species within this family, including apple maggots, western cherry fruit flies, walnut husk flies, and the dreaded Mediterranean fruit fly (Ceratitis capitata), or medfly. Unlike common fruit flies, members of this group lay eggs in leaves, stems, flowers, seeds, and roots, as well as in fruit. One member of this family, Euphranta toxoneura, deposits eggs in galls created by sawflies.
One species of fruit fly, D. suzuki, is new to California. This pest, also called spotted wing drosophila, has a taste for soft fruits, such as raspberry, strawberry, blackberry, cherry, and blueberry. There is not enough information available at this time to determine what sort of an impact these pests will have on those California crops, but it doesn’t look good.
Fruit fly controls
Outside of your kitchen, fruit flies are prey to robber flies, yellowjackets, ants, and certain beetles. Since ripe fruit is what attracts fruit flies in the first place, regularly harvesting fruit crops, such as tomatoes, melons, squash, grapes, and olives before they become overripe, can reduce fruit fly populations. Be sure to throw out the mummies, while you’re at it. Overripe potatoes and onions can also attract fruit flies. So can sink drains, mops, garbage disposals, trash cans, cleaning rags, recycling bins, and empty bottles. All fruit flies need is warmth, moisture, and something fermentable to eat. Eliminating any one of those three conditions can break the fruit fly triangle. Insecticides are not effective as long term controls, but pheromone traps can be used to interrupt fruit fly mating.
You can make your own fruit fly trap with a glass and a funnel. Simply place a piece of overripe fruit, some yeast and water, or cider vinegar, beer, or wine in the bottom of the jar and place the funnel on top, similar to a green fruit beetle trap. [Do not use apple cider flavored distilled vinegar - we may be fooled but fruit flies are not.] Fruit flies will be attracted to the bait and find their way in, but will be unable, for the most part, to find their way out. [If your funnel has spacers on the outside edges for air flow, cover the space with tape.] Every few days, take your trap apart and wash it with soap and water, before adding new bait. Within a couple of weeks, your fruit fly problem should be gone. Just be sure that you do not throw the contents of your trap in the trash, as it will contain hundreds of fruit fly eggs just waiting to hatch! Use soap and hot water to wash the glass and funnel. Let the hot, soapy water flow into the drain for at least one minute to wash any fruit fly breeding grounds out of your pipes.
As for those bananas you bought at the grocery store - rinse them off as soon as you get home. This will help to dislodge any fruit fly eggs before they can hatch. And refrigerating produce will halt the development of any fruit flies that remain.
Italian pear scale may sound like a lovely antique find at your local flea market, but this pest can reduce tree vigor and fruit size..
While it is easy to figure, from the name, that this pest attacks pear trees, it can also be found on walnut, prune, and apple trees.
Italian pear scale description
Italian pear scale (Epidaspis leperii) females are purple, pink, or reddish. Like other scale insects, they spends most of their life hidden under a tiny, grey, circular cover, with an off center peak. This cover is only 1.5 mm in diameter. For us Americans, that works out to only 1/16 of an inch! To make finding them even more difficult, they may be hidden under moss or lichen. Male flying scales are too small to see.
Damage caused by Italian pear scale
This insidious pest does not attack fruit or nuts. Instead, in the relative safety of their dome-like home, they feed directly on the wood of the tree. Large infestations can lead to cracks in the bark, which allows other pathogens to enter. The strain on the tree also reduces growth and production, resulting in smaller sized fruit or nuts.
Controlling Italian pear scale
After leaf drop, monitor trees for scale infestation. You may ned to scrape off moss or lichen to see these tiny pests. These scale insects seem to prefer scaffold limbs (the larger, horizontal branches). Heavy infestations can be treated with Bordeaux mixture.
Citrus thrips are not just a pest of orange trees - now they feed on blueberries, too!
As true bugs, thrips (Thysanoptera) are cousins to lice, both of which evolved from sap-sucking aphids. Citrus thrips are small, narrow-bodied insects that use rasping and sucking mouthparts to take nutrient rich sap from host plants. These pests are also vectors for disease. What puts citrus thrips in the news today is the way they are modifying their diet to coincide with human efforts at plant breeding.
Citrus thrips description
First, citrus thrips are very difficult to see. They generally hide underneath leaves and leap away, flying to another hiding place when they feel threatened. Since their wings are really not designed for actual flight, thrips use a method called “clap and fling” to become airborne. Basically, a thrips claps its wings together, above its back, and then flings them apart, over and over. This creates enough lift to get somewhere else, but that’s about it. If you actually get ahold of one, you will see that they have 2 pairs of very skinny, fringed wings and a narrow, cigar-shaped body. Newly emerged adults are pale yellowish-green, while adults are black with red markings.
Citrus thrips life cycle
Citrus thrips go through an incomplete metamorphosis called hemimetabolism. This means they have three distinct life stages: egg, nymph, and adult. Thrips are able to reproduce sexually, asexually, or bisexually. Dozens of eggs are inserted into leaf tissue. When they hatch, generally around March, the oval-shaped, clear yellow larvae start feeding on new growth, called “flush.” This causes distorted leaves and buds. Once the larvae have eaten their fill, they enter a resting pupal stage before becoming adults. With California’s mild climate, there can be as many as 8 generations of citrus thrips each year. That’s a lot of thrips!
As disease vectors, citrus thrips can carry tomato spotted wilt and up to 20 other plant viruses to your otherwise healthy plants! The real kicker is that, with the advent of heat-tolerant blueberry plants becoming popular in California, thrips have discovered a rich new food source! Citrus thrips damage to blueberry plants includes deformed leaves, shortened internodes (spaces between leaves), and stem scarring. While the fruit is not directly affected, the overall health of the plants is compromised, which leads to reduced plant growth and lower fruit production.
Controlling citrus thrips
To initially check for citrus thrips, simply go out in the morning and hold a piece of dark paper (or your other hand) under affected areas and shake the stem. Since adults can escape, count them first. Then count the nymphs. You may need a hand lens. Since this can also shake loose fruit before it has ripened, you have to sort through the pros and cons. Some varieties of blueberry, specifically Jubilee, Misty, and O’Neal are less appealing to citrus thrips than, say, Star, so choose your blueberry variety with that in mind.
Once bushes are installed, pheromone traps and yellow sticky traps are used successfully to monitor for adult citrus thrips populations. These populations tend to peak from mid-August through mid-September. Citrus thrips eggs are present year round, but there is little that can be done to eliminate them at this stage. Some people claim that using a high pressure spray from the hose can help, but research does not back up those claims. Commercial growers spray blueberries with industrial grade insecticides. Unfortunately, thrips are notorious for developing resistance to chemicals that are used repeatedly.
Organic growers must rely on spinosad and lacewing larvae to control citrus thrips. Currently, research is being conducted on an entomopathogenic pathogen (fungi that cause disease), called Beauveria bassiana, is being studied as a possible treatment. [I will keep you posted, as I learn more about that particular option.]
Symptoms of blackleg
Since cabbages don’t actually have legs, you may wonder how this name came about. The word ‘blackleg’ refers to dark lesions that first appear on stems at ground level. Each part of the infected plant has its own set of symptoms:
Infected stems are prone to snap. If you cut into the vein of an infected plant, you can see the blackened xylem - just be sure to disinfect your tools afterward!
Blackleg host plants
Blackleg fungi love California’s cool weather crops. This includes cabbage, broccoli, Brussels sprouts, cauliflower, Chinese cabbage, mustards, kale, kohlrabi, collards, radish, even turnips and rutabagas! Horseradish, though a member of the cruciferous family, seems to be resistant to blackleg. Blackleg can also infect potatoes and canola.
The fungal spores of blackleg (Phoma lingam) are often carried into your garden on seeds. Once they arrive, they can be distributed on tools, by splashing water, or infected plant material that has been cold composted. One spore type can also be carried on the wind. These fungi can also gain entry into otherwise healthy plants through cabbage maggot, cutworm, cabbageworm, and other pest feeding holes. It only takes a few fungi, with the right amount of warmth and moisture, to create an epidemic in a seed bed, garden row, or agricultural field. Blackleg can also refers to these other pathogens (and their host plants): Erwinia carotovora (delphinium) and Pythium spp. (geraniums).
Like many other garden variety diseases, prevention is far easier than cure. Protect your plants and your soil from blackleg with thee good practices:
Any time you see signs of blackleg, remove and destroy the plant and make a note of the location. You should not plant any cruciferous plants in that spot for at least three years.
Blister beetles may look harmless, but they use chemical warfare to defend themselves!
Blister beetle families
In California, there are three major groups of blister beetles: Epicauta spp., Lytta spp., and Tegrodera spp. [When reading Latin names, the “spp.” seen after the word is an abbreviation of “species.” It refers to all the species within that genus.]
Blister beetle identification
Blister beetles tend to be long and narrow. Their wing covers are soft and flexible. Adults are usually 1.2 an inch long. Depending on the species, these pests are usually black, gray, or green, and some have orange or yellow stripes. Some species are very colorful, warning would-be predators to think twice. Blister beetle species found elsewhere in the world can be metallic green, blue, reddish, or copper, with spots or stripes.
Blister beetle lifecycle
As far as insects go, blister beetles have a pretty interesting life. Female start the cycle by depositing fertilized eggs in low spots in the soil. The eggs hatch into larvae (called triungulin) , who hunt for underground cricket and grasshopper, and bee eggs. As they feed, they go through three growth stages before turning into sedentary pseudo pupae. This is their overwintering stage. As temperatures rise in spring, the pseudo pupae enter a true pupal stage before reaching adulthood. Adults feed on flowers and vegetable plants and breed throughout summer, depositing eggs in the soil, and the cycle continues.
Medical uses of blister beetles
Historically, dead blister beetles were dried and crushed and used on a variety of medical conditions, including gout, carbuncles, rheumatism, and impotence. The (ineffective) Spanishfly of legend is actually ground up blister beetles. The only safe and effective medical use for blister beetles is to remove warts. Even then, I would leave it to the pros.
If you see blister beetles in your garden or landscape, stomp on ‘em and then use gloves or some other barrier to pick them up and put them in the trash.
Harlequin bugs are black and red stinkbugs that feed on members of the cabbage family.
Harlequin bug description
The telltale shield-shaped back of the stinkbug family (Pentatomidae) make it easy to identify this garden pest. Also known as calico bugs, harlequin cabbage bugs, and fire bugs, harlequin bugs (Murgantia histrionica) are shiny black with yellow, orange, and red markings. They are often confused with Bagrada bugs, but harlequin bugs are significantly larger, and they lack the white markings of Bagrada bugs. Adults can reach 3/8 of an inch in length. If you allow yourself to get past the bit about how these are pests, they really are strikingly beautiful. That being said I still feed them to my chickens whenever I see them.
Harlequin bug lifecycle
These pests tend to lay their black-and-white striped eggs in November in the Bay Area. This is probably because that is when their favorite foods are being planted! Clusters of 12 barrel-shaped eggs are laid on leaves. Allowed to hatch, they will spread out as they go through four or five molts before reaching adult size, usually around March or April in the Bay Area. Harlequin bug adults often hide in weedy areas, or near blackberries.
Damage caused by harlequin bugs
Brussels sprouts, cauliflower, radishes, cabbages, horseradish, turnips, kale, and other cole crops are the harlequin bug’s favorite hosts. These sap-sucking pests chew on stems and leaves, leaving a trail of white or yellow blotches. Since they tend to use pheromones to congregate and attract mates, feeding damage can be extensive. Heavy infestations can cause plants to wilt, brown, and die.
Harlequin bug controls
Hand-picking in early spring is the best organic control for these pests. You can drop adults in a bucket of soapy water. You can step on them but, keep in mind, they are stinkbugs and they do smell bad when threatened. Also, since many members of the stinkbug family eat mustard, you don’t want to smack one that happens to be crawling up your arm or leg. Chemicals, called glucosinolates, are used by members of the mustard family for self-defense. Harlequin bugs use those chemicals for their own defense and it can burn your skin. My hens get any I find, without any problem.
Keep a lookout for these beautiful pests and their striking eggs. Enjoy them, and then end them.
Like us, plants are subject to many bacterial diseases.
Bacteria are found everywhere on earth. There are bacteria that live on the edges of volcanoes and bacteria that live in jet fuel. (How’s that for resilience?) Luckily for us (and our plants), most bacteria are beneficial. Even as you read, there are millions of bacteria living on and in you, helping you to be healthier. Plants have beneficial bacteria, too. Legumes, for example, have a relationship with Rhizome bacterium that help them to convert atmospheric nitrogen into a form they can use for food. Bacteria can also disfigure, dwarf, and even destroy many of your plants.
Pests and diseases are estimated to reduce crop and garden yield by 10 to 25%, depending on who you ask. That’s a big loss, considering how labor intensive gardening and farming are. Plant diseases are caused by bacteria, viruses, and fungi. You may be surprised to learn that fungi are responsible for 85% of all plant diseases. That being said, there are approximately 100 species of bacteria that cause trouble for plant growers. Most of these diseases are more commonly seen in the Tropics, but the bacterial diseases we do see are certainly worth learning about. But, first, what exactly are bacteria?
What are bacteria?
Bacteria are tiny one-celled beings, without a clearly defined nucleus, that can reproduce rapidly by simple cell division. There are two categories of bacteria: Gram negative and Gram positive. This is from a lab test called the Gram stain. When tested, the cell walls of one family of bacteria will stain purple (Gram positive), while the other family stains red or pink (Gram negative). Out of these two categories, countless types of bacteria emerge. They come in several shapes. They can be rods, spirals, spheres, or filamentous (“whiptails”). All bacteria go through the same basic life cycle phases:
The study of bacteria as pathogens
The first bacterial plant disease ever identified was fireblight (Erwinia amylovora). This happened sometime around 1877, just after anthrax, the first bacteria to be identified. Since that time, much has been learned about how these one-celled creatures help and harm our food crops and ornamental plants. But, to cause harm, they must first gain entry.
How bacteria enter plants
Unlike viruses, which inject genetic material to reprogram cells to make more viruses, nearly all bacteria grow in the spaces between plant cells, working to destroy the cell wall and consuming its contents. [One species, Agrobacterium, comes close to crossing the line between viruses and bacteria by genetically modifying their hosts to cause cancer-like growths called crown galls.]
Most bacterial diseases are transmitted by sap-sucking insects. Aphids, leafhoppers, nematodes, and psyllids are the most common disease vectors. Once these pests are infected with a bacteria, they carry disease to every plant they visit! As these pests feed, bacteria are inserted into the plant tissue.
Bacteria can also enter plants through natural openings, such as stoma, and through injuries caused by rubbing, thorns, or wind damage. Onion maggot, cabbage maggot, caterpillar, cricket, slug, and other pest feeding damage can also open the way for bacteria. Other physiological conditions that provide entry for bacteria include citrus fruit split, mummies, and your very own pruning shears!
One bacteria, Pseudomonas syringae pv. tomato, the bacteria responsible for bacterial speck, causes massive losses each year. Researchers at Virginia Tech discovered that this pathogen has figured out how to drop the bits of its own genetic information that were used by tomatoes to recognize it as a threat!
How bacteria damage plants
Bacteria have five basic methods of breaking through cell walls and consuming host plants:
Once inside, most bacteria grow between plant cells, in an area called the apoplast, or within a plant’s vascular system. As vascular bacteria reproduce, they clog either the xylem or the phloem, depending on the specific pathogen. If you’ve been following The Daily Garden, you will realize that clogging the xylem blocks the flow of water up from the ground, while interfering with the phloem starves the plant by limiting access to sugars produced by photosynthesis. Do you think the symptoms would be different? How so? Tell us your thoughts in the Comments!
Back in medieval times, it was believed that bathing would remove a protective coating that saved us from the Evil Spirits that caused death and disease. [Thank goodness those days are over!] In the same way, scientific research is changing the way we look at many bacteria. Some have been reclassified due to more accurate information. At this point, the most destructive plant bacteria fall into one of these families:
Acidovorax, Burkholderia, Pantoea, Ralstonia, Streptomyces, and Xyella are bacterial families that cause problems in other regions. To learn which bacterial diseases are likely in your area, contact your local Cooperative Extension Office. Two other unique bacterial families are fastidious vascular bacteria and phytoplasmas.
Fastidious vascular bacteria
Fastidious vascular bacteria were not properly identified until 1967. Up to that point, it was believed that many of the diseases they cause were actually the result of viruses. Two of those diseases are found in California. They are Pierce’s disease, which attacks grapes, and almond leaf scorch. These bacteria clog the vascular systems of plants.
This group of bacteria cause plants to produce more auxiliary buds, creating a bushier appearance, and weakening the plant in the process. Phytoplasmas are used by many commercial greenhouses to create plants with lush, thick growth. These bacteria also cause vivipary in strawberries. The same group of bacteria, carried by leafhoppers, cause corn stunt, cherry X-disease, and aster yellows in lettuce, celery, and other plants.
Symptoms of bacterial infection
Bacterial infection can be difficult to see, at first. Water-soaked lesions or bacterial ooze are often the first signs. Traditional symptoms of bacterial disease include leaf and blossom spots with yellow halos, cankers, galls, soft rots, or the classic shepherd’s crook stem ends of fireblight, and wilting. These symptoms vary, depending on the type of bacteria involved. Also, since bacteria are alive, they are constantly evolving to get the better of their hosts, pushing plants to evolve, which then pushes the bacteria, and so on.
Conditions that promote bacterial disease
Most bacterial diseases are seen in late April and early May in the Bay Area. This is because temperatures are rising, insects are active, there is enough moisture, and new, vulnerable buds and leaves are emerging. Most bacterial diseases prefer temperatures between 55°F and 85°F, with a highrelatve humidity.
Preventing and controlling bacterial disease
Bacterial disease is very difficult to control once it gets a foothold. Your garden plants will be far better off if you can prevent it in the first place. The following good cultural practices can make a big difference in the number of bacterial diseases affecting your plants:
Of bees, disease, and marigolds
Many garden resources point to honey bees and marigolds as protection from bacterial disease. There is even some measure of truth to these claims. Initial research, published in the Journal of Food Engineering suggests that the pollen bees carry with them may have antibacterial properties. Other research, from the University of Florida, shows that bees are the major vector of fireblight and southern bacterial wilt. As they move from flower to flower, they carry disease-causing bacteria with them. Marigolds, however, have been shown to provide protection against nematodes. Research conducted at the University of Florida found that planting a cover crop of marigold (Tagetes patula or T. erecta) can reduce nematode populations. Before you start planting, however, it is important to identify the specific nematodes in your soil so that you can select the correct marigold variety to get the desired results.
If you suspect bacterial disease in your garden, take a closer look and monitor regularly. Very often, you can break the disease triangle once you know what is growing on and in your plants.
Mummy berry is not a seasonal breakfast cereal. Instead, it is a fungal disease of blueberries.
This particular fungal disease is caused by the Monilinia vaccinii-corymbosi fungus. It is nearly always present in the soil, but a cool, wet spring can set the stage for serious losses.
Symptoms of mummy berry
A healthy summer blueberry bush is thick with leaves and twigs, blossoms and fruit. After a cool, wet spring, however, you may notice that some of the blueberries shrivel up, turning hard and grey. Before the fruit even appears, you may see a coating of brown or blue spores on the veins of infected leaves. You may also see drooping, wilting, brownish flower clusters that are turned in on themselves, before they turn brown and die. Immature fruit falls to the ground and twig tips become blighted in a condition called ‘shoot strikes’ and die. This is mummy berry.
The mummy berry mushroom spews fungal spores into the air, which then land on all this tender new plant tissue. Spores are also carried by pollinators, such as honey bees, wind, and water. Once the fungi reach your blueberries, they need adequate moisture to continue growing. According to research from Ag Canada, the following chart tells you the likelihood of infection at different temperatures, depending on how long leaves stay wet:
If you cut open an infected green berry, you can see white fungal tissue. [Afterwards, be sure to clean your cutting tools with a solution of one part bleach and nine parts water; or, you can spray your tools with disinfecting bathroom cleaner. If you don’t, you will spread the infection.]
Controlling mummy berry
Once infection occurs, all you can do is removed the diseased tissue and either burn it or throw it in the trash. You can reduce the chance of mummy berry causing too much damage in your garden with these tips:
Resistant blueberry varieties
Some blueberry varieties are more resistant to mummy berry than others. According to the USDA Agricultural Research Service, low bush varieties with less than 3% mummified berries include:
To enjoy the lush, sweet flavor of blueberries in summer, be sure to monitor your plants for signs of mummy berry!
Finally, I have some questions for you:
1. Do you like the new, tighter formatting?
2. What plant is giving you the most problems right now?
3. What plant or garden-related topic would you like to learn about?
Please reply in the Comments section. Thank you!
Witches' brooms are a common sight in autumn landscapes, but there is one variety that you will want to watch out for.
Witches' brooms are a symptom of plant disease or tissue damage, most commonly affecting woody plants, such as trees.
Symptoms of witches' broom
Witches' broom is easy to recognize. Where there is normally a single twig or stem, a clustered riot of shoots emerge, pointing in every direction. Stems may be twisted, discolored, or dwarfed. From a distance, it may look like a squirrel's nest, or an area of especially dense foliage. Closer inspection reveals a distinct deformity.
Causes of witches' broom
There are several conditions that can cause witches' broom. Some diseases, such as aster yellows and squash gourd mosaic can cause withes' broom. Sometimes it is a malfunction within a plant's hormone system. Auxin, a plant hormone that regulates plant cell growth, can be thwarted by a different plant hormone called cytokinen. Left to grow uncontrollably, stems grow in every direction, in every place possible. This burst of growth ends up looking something like a messy witch's broom, hence the name. Witches' broom can also be caused by bacterial plant parasites called phytoplasma. Phytoplasma were discovered in 1967 and no one has been able to recreate these pests in the laboratory. This makes studying them and developing control measures difficult. Fungi, mistletoe, mites, nematodes, and viruses may also cause this growth deformity. But sometimes deformities are not a bad thing.
The good witch
In some cases, the witches' broom that emerges is more of a dwarf version of the parent tree. Very often, that dwarf version can be removed and propagated. This is how many of our modern dwarf confers were first begun!
Bad for the kitchen garden
Witches' broom can wreck havoc in your vegetable garden. The same conditions that cause aboveground twigs to grow uncontrollably can make your carrot and other root crops inedible. There is no known cure for witches' broom and infected plants can spread the problem throughout your landscape. Your only recourse is to remove and dispose of affected plants in the trash. Do not compost them.
Preventing witches' broom
Unless you have the time to create new plant species, your plants will be healthier if you can prevent this problem in the first place. Phytoplasma catch a ride to your plants using leafhoppers, in a behavior called phoresy. Controlling leafhoppers can reduce the occurrence of witches' broom. Also, proper pruning, to remove dead and diseased branches, crop rotation, and general garden sanitation, can reduce the likelihood of witches' broom occurring.
If witches' broom occurs in your landscape, remove the affected stems several inches below the distorted area. Be sure to sanitize cutting tools with one part bleach and nine parts water afterwards and dispose of the affected plant material in the trash.
Cabbage maggots are a serious pest of plants in the cabbage family (Brassica).
What starts out as a single, tiny fly can turn into 300 squirming, gnawing slugs of destruction in just two or three days. And you may never see them before it is too late. Cauliflower and Brussels sprouts are more likely to be attacked, but broccoli, cabbage, turnips, radishes, rutabagas, and mustard plants are also vulnerable, especially in cool, wet weather.
Cabbage maggot description
Cabbage maggots are the larval stage of the cabbage fly (Delia radicum). Also known as cabbage root flies, root flies, or turnip flies, this dark grey fly is half the size of your average house fly. Maggots are white, legless, and only 1/3 of an inch long, with a pointed head and a blunt behind. Eggs are white and 1 mm in diameter.
Cabbage maggot lifecycle
Eggs are laid in the soil, around the crown of host plants. When they hatch, larvae (maggots) start feeding on fibrous roots and burrowing into taproots. This feeding facilitates entry by pathogens that cause blackleg and bacterial soft rot, and it continues for three weeks before maggots pupate in the soil. In two to four weeks, adult flies emerge to feed on nectar and the whole cycle begins again.
Symptoms of cabbage maggot feeding
These pests are easy to miss, but the damage they cause is obvious. As seedlings and young plants struggle to survive, chlorosis (yellowing), stunting, and even death may occur. Infested root systems are sparse and taproots show obvious tunneling. Established plants are better able to withstand attack, but they will also show stunting and chlorosis. Wilting in the middle of the day can also be a sign of cabbage maggot feeding. Plants will perk back up by morning, but, within a few days, they will be dead. Dark green leaves may show a bluish tinge, but that can be a normal feature of some plant varieties, so don’t use it as a symptom unless other signs are visible. Infested plants should be removed and destroyed. Do not compost infested plants.
Cabbage maggot control
If cabbage maggot carnage is something you need to control, spinosad is moderately effective, according to a 2015 UCANR study. Traditionally, fumigation was used, and organophosphates (diazinon and chlorpyrifos) were applied to soil in concentrations heavy enough to contaminate ground water and kill off non-target species. Obviously, more environmentally safe, sustainable methods are needed. Many of the other insecticides that performed the best in the study are unavailable to the home gardener, and for good reason. You can reduce the likelihood of infestation by using crop rotation, row covers, and proper irrigation.
If you are determined to protect your cole crops, you can also use brassica collars around the base of each plant. A brassica collar is simply a flat piece of plastic, thick cardboard, or heavy fabric that covers the soil around the base of a plant. Cabbage flies are unable to lay their eggs as close as they would like, and many of the larvae simply starve to death before they reach your plants. You can make your own brassica collar, just be sure that the collar opening can be enlarged as the plant grows.
You can grow a surprising amount of food in your own yard. Ask me how!