BY KYM POKORNY
Even on those hot summer days when a slamming screen door can’t stir up a breeze, a circus of activity is going on in the backyard. Insects are meeting, mating and devouring each other in their very own backyard Bugville. Now before you say “Ewww, bugs,” consider that those insects help keep your yard healthy without toxic insecticides.
It’s been a bug-eat-bug world for a long time — long enough that they’ve pretty much got the drill down. Unfortunately, humans tend to get in the way, building and fencing and spraying.
But there are ways to encourage the natural predatory process. Identification of good bugs vs. bad bugs will make the process easier. To help, we’ve provided profiles of some common insects in the Northwest. Robin Rosetta, entomologist with the
, has this advice for attracting beneficial insects to the yard:
— Tolerate low populations of pests so beneficial bugs have some prey. They won’t come if they don’t have anything to eat.
— Grow a diverse selection of plants, including those that attract insects. Some candidates: fennel, sweet alyssum, Queen Anne’s lace, parsley, yarrow, spearmint, hairy vetch, crimson clover, caraway, cosmos, bishop’s weed, blazing star, coreopsis, golden marguerite, sunflowers, candytuft and coriander.
— Provide shallow basins of water so they have something to drink.
— Avoid chemical insecticides that kill pests but also kill predators.
— Be patient. The good guys will come.
— If you decide to buy some beneficial bugs to add to the natural population in your yard, remember that you’ll need to release them more than once. Because most are shipped live and must be used right away, you’ll have to keep buying them fresh.
More a nuisance than a real pest, boxelder bugs want to move indoors for winter. If you can keep them out now, they’ll disappear once cold weather makes an appearance.
Eastern and western boxelder bug
About 1/2 inch long, brownish-black to black with distinctive red markings on its side and wings. In the immature stage, it is bright red.
Deciduous forests, gardens
In spring, adults emerge from winter shelter and fly to maple trees to lay eggs in bark crevices or on foliage. Eggs hatch in summer and young start feeding on tree foliage. In fall, adults leave trees to find a warm, dry place to spend the winter. There’s one generation a year.
WHAT IT BUGS:
Most common on female boxelder trees (
), hence the name, but also visits other maples and some fruit trees. It feeds on the leaves, which can cause some damage but usually very little. Humans are more likely to be annoyed because boxelder bugs tend to head for the house, sometimes in large numbers, during fall.
Caulk openings and cracks around doors and windows and repair screens. Get rid of debris and leaf litter near the house, especially around foundations, to reduce the shelter they need to overwinter. Don’t plant female boxelder trees. Vacuum up any bugs that get inside. Don’t squash bugs; they can leave a stain. If the problem isn’t severe, don’t worry. Boxelder bugs don’t bite, don’t carry disease and don’t reproduce inside the house. If you have a severe infestation, consult a reputable pest-control company.
Anyone who’s ever had a houseplant has seen mealybugs, fluffs of white that seemingly appear out of nowhere and turn to cottony masses overnight. They get their name from their mealy-looking coating.
More than 100 species, including obscure mealybug, cypress bark mealybug, long-tailed mealybug and citrus mealybug.
Mealybugs tend to congregate in large colonies on stems or leaves. Because all ages group together, various sizes will be seen in one area. Males, rarely seen, are tiny winged insects.
Bugs suck plant sap, weakening tissue and causing stunted, distorted, discolored, spotted or yellowed foliage. Large infestations can cause premature leaf or fruit drop. Mature plants rarely die but can look stunted and unhealthy. Mealybugs excrete honeydew as they eat, a sweet, sticky substance that promotes growth of sooty mold fungus, which looks like black goo on leaves.
You name it. Mealybugs are common on houseplants and in greenhouses.
In some species, females give birth to live young. In others, they lay as many as 600 eggs, which hatch within 10 days. Young nymphs crawl all over the plant and to other plants. Soon after they begin feeding, white waxy filaments appear, covering their bodies with cottony fluff. Mealybugs become less mobile as they mature.
Inspect plants before you buy. Indoors, isolate infected plants. Wipe off mealybugs with a soft, wet sponge, soft toothbrush or cotton swab dipped in alcohol. Outdoors, rinse plants with a stiff spray of water or spray with insecticidal soap. Encourage natural predators by planting wide range of pollen- and nectar-rich plants. Control ants that tend mealybugs for the honeydew they secrete. Use ant stakes at the base of affected plants or apply sticky material around trunks.
AZALEA LACE BUG
AZALEA LACE BUG
Azalea lace bug
Evergreen azaleas and rhododendrons
Eggs look like brown spots along the veins on the underside of evergreen azalea and rhododendron leaves. Adults are about 1/4 inch long and have wings covered with a network of black and white veins. Sometimes confused with the many species of lacewings, which are beneficial insects, lace bugs can be recognized because their wings lie flat; lacewings hold them up like a tent.
Lace bugs pierce leaves and suck out the chlorophyll, which causes yellow dots on the topside of leaves. You’ll see black feces on the underside of leaves. Eventually, foliage turns white, which is a sign the plant is not long for this world.
Lace bugs usually become active in mid- to late May and early June, when they start laying eggs, but can get going earlier during a mild winter. The bug is especially persistent because several generations are produced in one year, each one as hungry as the last.
Because of how fast they reproduce, control is difficult. Keep plants healthy by planting in part shade rather than full, watering regularly and mulching the soil.
Nontoxic methods of control include horticultural oil, insecticidal soap and neem-based products. Chemical insecticides kill important pollinators and beneficial insects that kill other pests.
Robin Rosetta, an entomologist with the Oregon State University Extension Service, has been conducting extensive research, including a sabbatical focusing on the pest insect. She has
Chemical insecticides are discouraged for home gardeners because of their negative impact on bees and other pollinating insects.
REALLY BAD BUGS
A TRIO OF TERRORS
TOMATO HORNWORM (covered with braconid wasp cocoons)
Tomato hornworm, corn earworm
imported cabbage worm
If you have a vegetable garden, you’ve more than likely run into one or all of these common pests, all hungry caterpillars when they do their damage. The most dramatic is the tomato hornworm, the most common is the cabbage worm, and the most serious in its economic impact to agriculture is the corn earworm.
COMMON NAME/LATIN NAME:
. Corn earworm/
. Imported cabbage worm/
With its large size (as long as 4 inches), distinctive markings and angry-looking horn, the
is enough to cause quite a start when glimpsed in the garden. The pale green caterpillar has diagonal white stripes, tiny black spots along the stripes and a larger, ringed black spot at the bottom of each stripe. In spite of its menacing looks, the horn at the rear is harmless. Adults are mottled gray moths with a wingspan of 4 to 5 inches and rows of orange dots along the sides of the abdomen.
grows to nearly 2 inches and varies from light green to pinkish-brown to black with stripes running lengthwise along the body. Whiskerlike spines sprout from dark warts on the body. Adults are night-flying, yellowish-tan moths with a wingspan of 1 1/2 to 2 inches.
IMPORTED CABBAGE WORM (with adult cabbage white butterfly)
are about 1 1/2 inches long with a fine, light yellow stripe down the back. Adults are the common white moths with black markings often seen in gardens.
All three of these troublesome critters overwinter in soil or on host plants in the pupae stage and emerge as adults around May, when they lay their eggs. After several days to a week, caterpillar larvae emerge to feed on our favorite veggies for two to four weeks. Then they pupate, emerge as adults and start all over again. There can be one to four generations per year.
WHAT THEY BUG:
As their name indicates, tomato hornworms prefer tomatoes, but they’ll also make dinner of potatoes, peppers, eggplant and tobacco plants. Corn earworms plague corn throughout the United States but will also attack tomatoes, peppers, beans, squash and sunflowers. Cabbage worms primarily eat anything in the cole family, including broccoli, cauliflower and Brussels sprouts. They appear to like red cabbage less than green cabbage.
All three worms are voracious foliage eaters and contaminate what’s left with their feces. Hornworms also will eat into green fruit. Corn earworms will eat down through the kernels and feed on developing tassels. In tomatoes, earworms leave deep watery cavities. Cabbage worms will chew on the heads of cauliflower and broccoli.
Floating row covers keep adult moths from laying eggs. Handpick caterpillars. Spray Bt (
) for cabbage worms or when hornworms or earworms are small. Many natural enemies, including wasps, green lacewings and soldier bugs, will attack these pests. If you see small white cocoons sticking out of a hornworm, it’s been parasitized by a wasp. For cornworms, apply a teaspoon of mineral oil to the tip of each ear of corn when silks appear, to deter egg-laying moths. Pinch the top of each ear with a rubber band to keep caterpillars out. Insecticidal soap can control small larvae, and insecticides with pyrethrum or neem are also recommended. At the end of the growing season, clean up debris and weeds that could be used as hosts or alternative food sources. Rotate crops.
This familiar insect may look spiritual as it perches with front legs folded prayerfully under its chin, but don’t be fooled. If anything, it’s praying for food while it waits to ambush its dinner. And, if that doesn’t convince you of deadly intent, its cannibalistic habits will.
Praying mantis or praying mantid
Stagmomantis carolina, Mantis religiosa
Long, thin, green or straw-colored body ranges from 3/8 inch to nearly 6 inches long. Two front legs are stout and strong, lined with sharp spines used to impale and hold onto prey. Thinner middle and back legs are used to grab hold of twigs or stems. Triangular head and bulging eyes give it a monsterlike look, especially when the head swivels back and forth or the praying mantis looks over its “shoulder,” a hauntingly human attribute unique in the insect world. Newly hatched offspring resemble their parents, only tiny.
Meadows and gardens throughout the world, particularly in temperate and tropical regions. Carolina mantid is native to the United States. Chinese mantid was introduced in 1896 as a beneficial insect. European mantid was accidentally introduced in 1899 on nursery stock. Because they do not live through cold winters, praying mantises are not as common in Oregon and Washington as they are farther south.
During fall mating, the smaller male hops onto the back of the female. If he misses, he can become dinner for his darling. Even if he doesn’t, the female may turn and devour his head while mating. But no matter; his body is capable of completing mating even without his head. When mating is completed, the female, hungrier than ever, will finish eating her hapless mate. Then she lays groups of 12 to 400 eggs, which are covered in a frothy liquid that turns into a hard, protective shell. In spring, baby mantises emerge, often eating each other as their first meal. Cute, aren’t they?
WHAT IT BUGS:
Almost anything that moves is fair game. Baby mantises tend to go for aphids and other small, slow-moving insects. Larger ones prey on all manner of insects, including honeybees and other pollinators. They’ll even dine on salamanders, toads, frogs, lizards and hummingbirds.
WHY WE LIKE IT:
Well, it’s cool-looking and has interesting habits. Although often touted as a beneficial insect, the praying mantis is pretty ineffectual as a biological control. They produce only one generation a year, so their population can’t increase in response to rising pest populations; they’ll eat each other, especially when young, further depleting their population; they tend to eat fast-moving insects instead of poky aphids, caterpillars and beetle larvae that bother gardens; they hang out and wait for prey to come to them; and they eat beneficial as well as pest insects. That said, it’s worth buying an egg case to watch them hatch, especially if you have children in the house. They will disappear if there aren’t other bugs to eat, but some will probably hang out. To keep them around, don’t use chemicals, and plant some tallish meadow plants (they particularly like goldenrod) for cover.
Myths about praying mantises abound. One comes from the Chinese, who believe that these insects have curative powers, including the ability to stop children from wetting the bed when they eat the roasted egg cases. Needless to say, no one in the United States is lining up to volunteer as a test case.
Ethereal and delicate, the adult green lacewing lives up to its name. But the fragile appearance belies its predatory nature.
Green lacewing; larvae are sometimes called aphid lions
Slender, delicate and about 1/2 inch to 3/4 inch long, the adults are a pale green with netted wings held upright over their bodies. They have copper-colored eyes and long antennae. The larvae look like tiny alligators with visible legs and pincers. Light brown or green and spotted or striped, they usually reach about 1 to 1/2 inch at maturity.
To keep their young from eating one another, adult lacewings lay eggs singly on delicate, threadlike stalks attached to stems or leaves. In a week or two, the eggs hatch, and larvae begin crawling around, looking for prey. After feeding for a week or two on aphids and other bugs, they spin yellowish, pea-sized pupae, usually on the undersides of leaves. Winged adults emerge in about five days, mate and lay eggs. Lacewings die when weather gets cold, or they overwinter in the pupal stage.
WHY WE LIKE THEM:
Lacewing larvae are more ravenous than teenagers. They devour aphids faster than boys eat hamburgers and slurp down mealybugs, whiteflies, thrips, mites and small caterpillars.
HOW TO KEEP THEM AROUND:
Grow nectar plants such as coreopsis, cosmos, alyssum, angelica, coneflower, yarrow and fennel to attract adults. Buy eggs or larvae to release in the garden. More than one release might be needed to control large infestations.
Unlike the old nursery rhyme that implores ladybugs to “fly away home,” gardeners should beg them to stay. Perfect guests, ladybugs work hard to rid the garden of aphids and other pests and do no harm.
Ladybug or ladybird beetle
Hippodamia convergens, Harmonia axyridis
One of the most familiar and beloved (if you can love a bug) insects in the world, lady beetles are commonly red or orange with black spots. But they also can be yellow with black spots or solid red, orange, black or yellow. The larvae resemble tiny, six-legged alligators with a rough hide of gray or black with a little orange.
Females lay clusters of long, orange eggs on host plants. The eggs hatch into ravenous larvae that quickly begin searching for prey. The larvae pupate and emerge as adults, ready to fly and find a mate to start the cycle again. Adults of some species overwinter in garden debris.
migrates to the foothills of California for winter, where it is collected for sale to the public.
WHY WE LIKE THEM:
Lady beetles devour soft-bodied insects, especially aphids but also mites, mealybugs and soft scale. Larvae eat even more than their parents.
ONE BAD HABIT:
Ladybugs can invade houses and sheds by the hundreds in fall looking for shelter through the winter. In large numbers, they produce an odor that’s not so pleasant. Screened doors and tight seals on windows help keep them at bay. So do screens over attic and exhaust fans. If they get in anyway, a vacuum is an efficient way to get rid of them. No insecticides are legal to use on lady beetles.
HOW TO KEEP THEM AROUND:
Buying ladybugs is usually not successful. Collected ladybugs usually have not matured eggs and are ready to migrate, so they fly away as soon as they are released. Some suppliers sell preconditioned ladybugs that have matured eggs, but even these will take off if there isn’t plenty of food. Encourage a long stay by growing plants they can use for food and shelter, such as yarrow, sweet fennel, angelica, coreopsis, cosmos, dill and goldenrod.
WHERE TO FIND BENEFICIAL INSECTS
Many nurseries carry ladybugs and praying mantis egg cases. Or, contact one of the following suppliers, which sell a wide variety of beneficials.
Evergreen Growers Supply,
March Biological Control,
* Hartfourd-Courant has more on
, including information on syrphid flies, predatory midges, parasitoid wasps, predatory bugs, spiders dragonflies and damselflies.
* Organic Gardening has a downloadable chart to 50 help
* Marci Degman of the Hillsboro Argus has information on
- Sap beetles
- How to protect your plants from sap beetles
- The Asparagus Beetle: Organic Control Tips
- Asparagus Beetle Reproduction
- Natural Enemies of Asparagus Beetles
- Organic Asparagus Beetle Control
- More Organic Pest Control Advice for Asparagus Beetles
- Asparagus Beetle Overview
- How To Get Rid Of Asparagus Beetles
- Frequently Asked Questions
- Asparagus Beetle, Common
- Life Cycle:
- Crop Injury:
- Monitoring & Thresholds:
- Cultural Controls & Prevention:
- Chemical Controls & Pesticides:
- Biological Control:
- Crops that are affected by this insect:
How to protect your plants from sap beetles
Watch for sap beetles in gardens starting in early July when adults first start to emerge. Particularly check overripe strawberries, although they can also be found in ripening fruit.
Remove overripe fruits and vegetables
Remove any damaged, diseased and overripe fruits and vegetables from the garden at regular intervals.
Collect apples, peaches, melons, tomatoes and other decomposing fruits and vegetables and bury them deep in the soil or destroy them to eliminate beetle food sources.
Using baits for trapping
You may try bait trapping to reduce beetle populations.
- Place traps that are more attractive than ripening fruit. Trap buckets baited with whole wheat bread dough and over-ripe fruit outside the patch helps to reduce beetle numbers.
- A container of fermenting plant juices will also attract sap beetles.
- Common baits include stale beer, molasses-water-yeast mixture, vinegar or any overripe fruit.
- Traps should be placed a few feet outside of your garden.
- Discard trap contents frequently, every three or four days and rebait traps.
Use of pesticides is NOT very effective and is NOT recommended. Sap beetles are seen on ripe fruit, so pesticides should NOT be used on the crop.
Carbaryl and bifenthrin can be used to control severe infestations. These pesticides may kill existing beetles, but if fruit/vegetables are present, they cannot prevent additional sap beetles from moving into gardens.
CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.
Be sure that the fruit/vegetable you wish to treat is listed on the label of the pesticide you intend to use. Also be sure to observe the number of days between pesticide application and when you can harvest your crop.
The Asparagus Beetle: Organic Control Tips
Asparagus Beetle Reproduction
Soon after emerging in spring, asparagus beetles lay eggs on emerging spears, which hatch in three to eight days. The small soft-bodied, grayish grubs feed on the tender new growth in spring. Later in summer, eggs and larvae can be found feeding on asparagus foliage. When the grubs mature after about two weeks of feeding, they drop to the ground and pupate inside an earthen cell for seven to 10 days before emerging as adults. In most climates, there are two generations each year, but in warm climates there may be as many as five generations of this asparagus pest.
Spotted asparagus beetles emerge in midspring and promptly begin eating asparagus foliage, but they wait until asparagus plants develop berries to lay their eggs. After the eggs hatch, the larvae bore into the berries to feed.
Natural Enemies of Asparagus Beetles
Birds often eat asparagus beetles and larvae, which appear during nesting season when birds need more protein. Lady beetles eat young larvae, but the most effective predator is small black Eulophid wasp (Tetrastichus asparagi),which eats asparagus beetle eggs early in the season, and lays its eggs in asparagus beetle eggs in summer. This beneficial insect, which is so helpful with asparagus beetle control, was identified in Massachusetts in 1915 and is now found wherever asparagus is grown. It is not currently offered for sale commercially.
Organic Asparagus Beetle Control
When dealing with the asparagus beetle, organic control methods can be quite effective. One key is to remove plant debris from the patch in fall and compost it in an active compost pile. Larvae and adults can be removed by hand. When handpicking, place a pail of water on the ground, and many beetles will drop into it when knocked from the plants. Beneficial wasps will parasitize beetle eggs. Chickens also do a good job of gathering asparagus beetles when allowed to forage in the patch in late summer. In severe situations, you can get good organic control of asparagus beetles by spraying plants with neem early in the season, when populations are modest. Do not use neem or any other pesticide if small black wasps are present in your asparagus patch.
Spotted asparagus beetles will be discouraged if the asparagus planting is male-only cultivars that do not form berries. If your plants do produce berries, gather and compost all asparagus berries if spotted asparagus beetles have been seen. This is the best organic asparagus beetle control.
More Organic Pest Control Advice for Asparagus Beetles
Reduce populations of overwintering adults of both asparagus pests by keeping the surrounding area lightly tilled and by eliminating plant debris. This forces asparagus beetles to hibernate in soil, where subsurface predators eat them.
In early spring, cut spears promptly at ground level with sharp knife. Attentive harvesting will keep many asparagus beetle eggs from hatching.
Both kinds of asparagus beetles can be easily handpicked. A beetle’s instinct is to drop to the ground when it feels disturbed, so hold a container of water under the plant before gently shaking it, and the bugs will drop into the water. A sheet or newspaper or pizza box works well, too.
Asparagus is a great crop to grow. This perennial produces delicious spears every year in the spring. But there is a down side to growing this phenomenal edible… the asparagus beetle.
You might not be alarmed when you see the first couple asparagus beetles, but if they’re not dealt with quickly, you will have a perennial problem right along with your perennial vegetables. So what can you do to battle the beetle? Read on, and I’ll tell you everything you need to know about asparagus beetles and how to get rid of them.
Good Products To Eliminate Asparagus Beetles (in order):
- Monterey Garden Insect Spray
- Safer Brand Home And Garden Spray
- Beneficial Nematodes
- Neem Oil
- Harvest-Guard Floating Row Covers
Asparagus Beetle Overview
|Common Name(s)||Asparagus beetle, common asparagus beetle, spotted asparagus beetle|
|Scientific Name(s)||Crioceris asparagi, Crioceris duodecimpunctata|
|Plants Affected||Asparagus. Spotted asparagus beetle may also affect some cucurbits.|
|Common Remedies||Spinosad and pyrethrin sprays, ladybugs, lacewings, parasitic wasps, beneficial nematodes, neem oil, floating row covers|
Types of Asparagus Beetle
While technically there are four known types of Crioceris, only two have been recorded in modern times. Here’s some information about how to identify these two types.
Crioceris asparagi, ‘Common Asparagus Beetle’
Source: TJ Gehling
If you see an odd-colored beetle that’s a bluish-black in color with red and white, it might be the common asparagus beetle, Crioceris asparagi. The common asparagus beetle is mostly blue-black, but has cream-colored or pale yellow spots along its back, and an orangish or reddish border to its wings. It has an elongated head with feathery-looking antennae. This is by far the most common asparagus beetle variety, and the one which is most devastating around asparagus plants.
Crioceris duodecimpunctata, ‘Spotted Asparagus Beetle’
Source: Ettore Balocchi
The spotted asparagus beetle is often mistaken as a weird ladybug, but this is no beneficial insect. Often seen as a pumpkin-colored orange beetle with black spots in the western United States, or a medium to dark red beetle with black spots in the east, it is similar in some regards to a ladybug… until you look at its elongated head and almost feathery-looking antennae. The spotted asparagus beetle is not as destructive to asparagus, but still feeds on it, as I’ll explain a little further on.
Asparagus Beetle Life Cycle
The asparagus beetle likes to overwinter in leaf litter or other debris near its food, sometimes even inside the hollow stems of older asparagus plants. As spring comes and the first signs of new asparagus shoot growth occurs, the adult beetle will also emerge from its winter hiding space. They start by having a snack to replenish themselves, feasting lightly on the tips of the new shoots.
Once satiated, adult asparagus beetles will begin laying brown, pill-shaped or oval eggs in neat rows. These will be either on the spears themselves (for the common asparagus beetle), or on the ferns or flowers (frequented by both types). It should be relatively easy to see these eggs as they visibly jut out from the fern or spear, creating an almost spiky-looking line along it.
The eggs hatch within seven days, creating small larvae. The common asparagus beetle larvae migrate to the ferns and begin to feast upon the plants, and neither the ferns nor the shoots will be safe. The spotted asparagus beetle’s larvae prefer the berries that are formed by the flowering plants to the foliage itself.
Spotted asparagus beetle larvae are typically darker in color than the common asparagus beetle larvae. Both are grey-green in coloration, and finding them requires close attention, as they blend in quite well with the foliage of your plants.
Approximately two weeks after emerging from the egg, the larvae are now prepared for pupation. They drop from the plant down into the soil, dig under the surface, and form a cocoon there. It takes about a week for the larvae to pupate and then emerge as adults, and then the cycle begins again.
Two to five life cycles can happen in a year’s time, depending on the weather conditions where the plants are. Colder climates have fewer life cycles.
Common Habitats For Asparagus Beetles
Both types of asparagus beetle inhabit North America, but the spotted asparagus beetle is far more common on the eastern half. The common asparagus beetle is throughout the country.
As a general rule, the asparagus beetle spends the majority of its life in, on, under, or beside asparagus plants. What time isn’t spent around asparagus is generally spent trying to locate a new asparagus plant to dwell on.
What Do Asparagus Beetles Eat?
Source: The NYSIPM Gallery
While I would say that this is pretty obvious, it’s not… because the spotted asparagus beetle is more culinarily-diverse than its cousin.
While common asparagus beetles are fixated on only asparagus plants, which makes them a major problem for farmers of the crop, the spotted asparagus beetle has been known on occasion to get a taste for cucurbits. It can occasionally lay eggs on the flowers of these plants, and on occasion the larvae will snack on newly-forming melons or squash. However, it really prefers the berries of the asparagus fern, and so it’s most likely to be found there where all of its nutrition needs are fully met.
You can identify when an asparagus beetle is feeding on your plants when there are holes or pits in the leaves, stalks, or plant structure. Anywhere that one has been feeding will turn brownish in color. The tips of the spears themselves may also turn brown. After excessive feeding, the plant may appear to be shriveled and stunted.
How To Get Rid Of Asparagus Beetles
So now that you know what you’re looking for and what it’s likely to be attacking, how do you eliminate these annoying little beetles from your perennial beds?
While it’s generally recommended that you use these options in limited amounts, especially on young asparagus stalks, use of a few spray insecticides can help you kill asparagus beetles and their larvae. For asparagus, it’s best to spot-treat with these when you discover adult or larval asparagus beetles, rather than doing widespread spraying when it’s not necessary.
Please remember that some insecticides are harmful to bees. While the ones I’m mentioning are less dangerous to pollinators, it’s a good idea to try to avoid spraying the asparagus spears when the tops have gone to bloom.
Spinosad sprays, such as Monterey Garden Insect Spray, can be used quite effectively to control a number of beetles and caterpillars, leaf miners and thrips.
Also, pyrethrin sprays are a common way of enacting asparagus beetles control. You can opt for a pure pyrethrin spray such as PyGanic, or you can choose a spray with other active ingredients such as Safer Brand Home And Garden Spray. Both work extremely well against most beetles, caterpillars, and a host of other common pests.
Environmental Asparagus Beetle Control
Use beneficial insects to help keep the egg population down. Ladybugs and lacewings will happily eat the asparagus beetle eggs and stop larvae from being born.
While it’s not commercially available, there is a beneficial parasitic wasp that is naturally attracted to asparagus in the wild. This tiny wasp, Tetrastichus asparagi, will lay its eggs in asparagus beetle larvae. When the eggs hatch, the larvae will be consumed by the young wasps. As long as you do not use any pesticides that are harmful to wasps, this insect will arrive on its own and take up residence nearby.
Birds love to eat both the adult form and the larvae of asparagus beetles. If your asparagus patch is bird-friendly, they will help you with asparagus beetle control.
Beneficial nematodes are a great thing to have in your soil! These microscopic soil organisms will help you by killing the larvae in their pupa beneath the surface of the soil or in leaf litter. They also protect against other pupating insects such as potato bugs, fungus gnats, and cutworms.
Preventing Asparagus Beetles
Watch your plants closely in late April and early May as the new stalks start to appear. If you can catch the overwintering adults quickly after they make their way out of the surrounding soil and hand-pick them off the plants, you can prevent egg laying.
A quick harvest of spears as soon as they’ve reached a reasonable length is the best way to discourage asparagus beetles, as it cuts short their life cycle. If the adult beetle can’t eat the fresh asparagus tips, it won’t stick around. However, be sure to check your plants as you harvest to ensure there are no eggs on the plant or on the stalks you’re cutting.
Using a soft-bristled brush to knock eggs and larvae off of the plant is generally a good idea, provided that you are careful not to damage the plant. Most larvae dislodged this way will lack the energy to climb back up and return to eating, and will subsequently die on the soil’s surface.
If you’re very sure that you don’t have overwintering asparagus beetles in your soil, you can keep a floating row cover over your plants. You can also add a floating row cover after all overwintering beetles are likely to have come out of the soil, provided that you are very sure there aren’t eggs, larvae, or adult asparagus beetles on your plants. After all, you don’t want to secure the plants with their natural predator right there!
Using a product such as neem oil can also prove to be beneficial. While it will not necessarily kill off the asparagus beetles, neem oil does dissuade them from snacking on your garden. It also has the added bonus of being human and pet safe, and it’s safe for most beneficial insects as well.
Frequently Asked Questions
Q: I am having problems catching adult beetles. Help!
A: One of the worst things about asparagus beetles is that they do fly. What I’ve found that works when hand-picking them is to have a container of soapy warm water on hand. Carefully slip the soapy water beneath the beetle on the plant, then come down at them from the top. They usually will fall right into your soap-water. Coming at them from the front or the sides seems to give them more warning and they can escape easier, but they don’t seem to see things coming from above as well.
Q: Are there companion plants that repel asparagus beetles?
A: The problem with companion planting in asparagus beds is that the asparagus itself is a very heavy feeder as a plant. Most gardeners try to keep everything other than asparagus out of their asparagus beds, including any and all weeds, companion plants, etcetera. But if you do want to try companion plants, look at light-feeding herbs. Parsley is a great choice in an asparagus bed, especially if you get it started early enough that it surrounds the young spears as they emerge. It has an aroma that keeps asparagus beetles away, and it can live in even the most nutrient-deprived soil, making it less of a competitor to the asparagus itself.
French and Mexican marigolds can also repel asparagus beetles, but it might be better to surround your asparagus bed with them rather than planting them amidst the asparagus crowns, although marigolds also offer protection from nematodes and other plant problems if they’re close by. Petunias also act as a deterrent plant for asparagus beetles, but again, it’s better to plant nearby rather than directly in the middle of the asparagus patch.
While asparagus beetles are horrible to any lover of fresh spring asparagus spears, these tips can help you to keep them at bay and protect your future harvest. Do you grow asparagus, and if so, have you had problems with the asparagus beetle? Tell me in the comments!
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Asparagus Beetle, Common
There are two beetle pests of asparagus, the common asparagus beetle and the spotted asparagus beetle. Distinguishing between the two species is important because while both beetles can damage the emerging spears, the common asparagus beetle larvae and adults can also devour the ferns. Significant defoliation can weaken the plant and reduce the plant’s ability to provide sufficient nutrients for the following season. Serious defoliation can also make asparagus more susceptible to invasion by plant pathogens. The feeding of spotted asparagus beetle larvae on berries does not affect the health of asparagus plants over the long run.
Common asparagus beetle is blue-black, shiny, smooth and 6-9 mm (⅜ inch) long. The most distinctive markings are three large cream-colored, squarish spots with red margins along each wing cover. The head, legs and underside are blue-black, and the thorax is reddish. Eggs are dark brown, laid standing on end in rows along the spears, with 3-10 in each cluster. Larvae are wrinkled, plump, hump-backed, and dull gray or brown with black head and legs. They go through four growth stages (instars) and grow up to about 8 mm (⅓ inch). Pupation occurs in the soil, and pupae look similar to adults except for yellowish coloration.
Adult beetles overwinter in field borders or within asparagus fields. Sheltered sites such as under bark or in the stems of old plants are preferred. Some burrow into the soil. Adults emerge in early May and colonize asparagus fields to mate, feed, and lay eggs. Eggs hatch in 3-8 days, depending on temperature. Larvae feed in spears and ferns, and when mature, drop to the soil to pupate. There are 2-3 generations each season, with the first generation producting the most eggs. Second generation larvae feed in ferns. The temperature threshold for larval development is 10°C (50°F). In September, new adults search for overwintering sites.
Adult feeding on spears causes scarring and browning. Presence of eggs and feeding damage can render the crop unmarketable. Both adults and larvae feed in ferns and can reduce the plant’s ability to build resources for a strong crop the following spring. Damaged plants are also more susceptible to infection by the fungal pathogen, Fusarium.
Monitoring & Thresholds:
Begin scouting early in spring and continue through the summer. Scout for adults on sunny afternoons, when beetles are more active. Scout by sampling 10 plants in each of 5-10 different locations. Beetle distribution across the field tends to be clumped. Count adults, eggs, larvae, and take note of the damage to each plant. Consider treatment if >10% of the spears are infested with beetles (1 or more per plant) or 1-2% have eggs or damage. Treat ferns if 50-75% are infested.
Cultural Controls & Prevention:
- During harvest, harvest all spears every day to reduce the number of stems where eggs will survive for long enough to hatch or where larvae can feed and grow into summer-generation beetles.
- Disk old ferns lightly in the fall and clean up crop edges to reduce overwintering sites.
- Maintain clean environment in asparagus fields in the fall to force adults to overwinter in field edges where natural predators reside.
- Allow plants in one area to develop ferns so as to act as a trap crop. These plants can then be sprayed selectively.
Chemical Controls & Pesticides:
Daily harvest of asparagus makes chemical treatment difficult. 1 dh products are available and can be used immediately after picking to allow harvest the following day (see the New England Vegetable Management Guide for current recommendations) although some growers seek to avoid applications during harvest. More selective products may be used on fronds after harvest.
Organic options on spears include Surround WP as a repellent, EC5.0, or products containing capsaicin (check for certification status).
If possible spot spray along edges of planting where overwintering adults colonize the field and/or band insecticide over the row to help spare natural enemies. Use selective insecticides on ferns.
The most important natural enemy of common asparagus beetle is a tiny parasitic wasp (Tetrastichus asparagi) that attacks the egg stage. Wasps kill eggs by feeding on them. These parasitoids also lay their own eggs inside the beetle eggs. The immature wasps grow inside the beetle larvae, killing them when they pupate. Studies have found >50% of eggs killed by feeding and half of the surviving larvae parasitized. Providing a nearby nectar source such as umbelliferous flowers may enhance wasp populations.
For current information on production methods (including varieties, spacing, seeding, and fertility), weed, disease, and insect management, please visit the New England Vegetable Management Guide website.
Crops that are affected by this insect:
–R. Hazzard. References: Handbook of Vegetable Pests by John Capinera; 2008-2009 New England Vegetable Management Guide; Eric Sideman, MOFGA; Brian Caldwell, Cornell Universtiy, Suzanne Wold-Burkness and Jeffrey Hahn, UMI Department of Entomology.