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MIDNIGHT GARDEN MARAUDERS

written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA

‘Midnight marauders’ were the topic of one of my columns a while back. Before I launched an updated version this week, I checked to see when I wrote the previous one. It was in May of 1989. It’s definitely time to bring you up to date on the creatures that plunder our gardens under the cloak of darkness.

If no culprits can be found feeding on damaged plants during the day, the best way to determine what miscreants are at fault is to venture out after dark with a flashlight and catch them in the act. Here are the culprits you’re most likely to find.

SLUGS: Many gardeners new to the area don’t think we have slugs here, but area gardens do host these slimy mollusks that munch on plants at night. Sometimes in early morning you can see a glistening trail of slime that they’ve left behind on plants. Slugs will feed on both the tender leaves of young plants, as well as the tougher leaves of older plants. On older plants their damage is characterized as ragged chewing. On younger plants they devour large parts or entire young seedlings. According to WSU Hortsense, additional evidence of their presence includes ‘pretzel‑shaped’ fecal droppings.

EARWIGS: Most area residents are familiar with earwigs, those reddish brown fast-moving insects about three-quarter inch in length with a set of pincers at the end of their abdomen. During the day they like to hide in dark, moist tight spaces. I suspect they’ll be numerous in area gardens this year because they prosper when spring and early summer weather is wet.

These omnivores are considered beneficial because they feed on insect pests like aphids and mites, but they also feed on tender plant tissues, such as young seedlings and delicate flower petals. They can decimate seedlings, but on older leaves their feeding is characterized by small to large irregular holes and damage along leaf edges. On the surface of ripe soft fruit, including peaches and strawberries, they’ll leave shallow holes. Earwigs also feed on corn silks interfering with kernel formation.

CUTWORMS: Cutworms are the larvae or caterpillars of night flying moths and get their name because some cutworms eat around the base of young plant stems which results in ‘cutting’them off. Cutworms are not remarkable in appearance. They have hairless tan, gray or greenish bodies with various indistinct markings. Ranging from one quarter to one inch in length, they curl up when disturbed. They hide under plant litter, soil, and mulch during the day. Their main source of food is weeds, but they also feed on garden plants.

ROOT WEEVILS: Root weevils are another pesky nighttime insect. The adult weevils are black to brown snout-nosed beetles about one quarter to one half inch in length. Their damage is characterized by notching of leave edges, making them look like someone has cut along the leaf edge with pinking sheers. Root weevils attack over 100 plant species but seem particularly fond of lilac, euonymus, strawberries, peony, rose, rhododendron, and azalea. During the day they hide under plants in loose soil or plant debris.

If you go to bed as soon as the sun sets or you

re nervous about looking for nocturnal pests in your garden after dark, you can try trapping the offenders by placing damp, tightly rolled up newspapers near the plants under attack. Check the traps in the morning for slugs, earwigs or root weevils. Next week we’ll talk about what control approaches work best for these midnight marauders.

Published: 6/15/2012 2:54 PM

CONTROLLING ROOT WEEVILS IN THE DEAD OF NIGHT

written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

I was talking with a Master Gardener the other day about the root weevil problem in his little blueberry patch. Root weevils are a group of specialized brown or black snout-nosed beetles that attack a variety of ornamental plants.

Root weevil damage is characterized by notching of plant leaf edges. (They don’t eat holes in leaves.) Generally, this notching is a cosmetic concern and seldom does significant injury to a plant, but when their numbers are extremely large they can damage plants.

The weevil’s white C-shaped, legless larvae develop in the soil, feeding on the plant roots, root hairs, and the root crown at the base of the stems. The larvae can cause serious damage in potted nursery plants and in very sandy soil.

Most gardeners only note the notching damage and seldom see the actual weevil adults. That’s because during the day the adult weevils hide out in the soil and debris at the base of plants. After dark they come out and climb up the plants to feed on the leaves.

With the demise of many harsh garden pesticides, root weevil control has been particularly difficult to achieve, especially on food producing plants like the blueberries. That’s why the Master Gardener has been trying to collect them off his plants on a nightly basis to reduce their numbers.

Because adult root weevils will drop from the plant and “play dead” if disturbed at night when feeding, he was able to spread a cloth under his plants to collect the adults. After dark he went out at midnight and shook the plants. However, he encountered a problem. No weevils dropped off at that time. However, when he went out at 2:30 a.m. he was able to collect 15 per plant. He did this for several nights in a row, collecting about 15 weevils each time. He stopped when the number dropped to just one or two.

Curious about root weevil behavior, I called WSU Extension’s resident root weevil expert, Sharon J. Collman. She has done extensive research on these creatures for her PhD thesis.

Collman found 14 different species of root weevils in the Pacific Northwest during her 450 nocturnal collections of weevils. The black vine weevil (Otiorhynchus sulcatus), the obscure root weevil (Sciopithes obscurus) and the strawberry root weevil (Otiorhynchus ovatus) are the most commonly known root weevils that she found. She also found that the lilac or privet weevil (Otiorhynchus meridionalis) was the most common and often dominant species in eastern WA gardens and landscapes.

Collman notes that research on the effectiveness of specific insecticides for control of root weevil adults is limited, with 60 per cent of the studies researching the control of black vine weevil and only a limited number of studies (0 to 20 per cent) looking at the other 13 species found in our region. Some studies indicated that pesticide efficacy differed from species to species. This points out that what works in one region, may not work in another.

WSU recommends using acephate, cyfluthrin, neem oil, befenthrin, and azadiractin to control root weevils on ornamental plants like lilac and rhododendron. They recommend malathion for control on berries, such as blueberries. However, depending on the actual type of root weevil doing the damage, you may find these are not extremely effective. It may come down to setting the alarm clock and going out in the dead of night to shake the weevils from your plants.

Published: 10/11/2012 11:24 AM

ROOT WEEVILS NOTCH PLANTS

written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

Tomato hornworms gorge themselves on tomatoes. Colorado potato beetles devour potatoes. The corn earworm feasts on corn. Root weevils nosh on over 100 plant species including lilac, strawberries, peony, rose, raspberry, phlox, rhododendron, azalea, cotoneaster, Euonymus, clematis, yew, many different weeds, and more. The numerous small (no more than one-eighth of an inch wide) notches are characteristic of the feeding damage caused by these snout-nosed beetles, commonly called root weevils. They feed only on the edges of leaves because their snouts gets in the way, making it impossible for them to eat holes out of leaves.

Root weevils are nocturnal feeders, so these culprits are usually not found when sought during the day. If “seeing is believing,” you can go out on a summer evening after dark with a flashlight to look for them. During the day the root weevils hide under mulch, plant litter, or in crevices in the soil.

There are numerous different types of root weevils, but the two most commonly found in our area are the black vine weevil (BVW) and the strawberry root weevil. The adults of both have a shiny brownish-black to black oblong body. Their head elongates into a snout and their abdomen is covered by hard wing covers with parallel ridges. The BVW is up to one-third inch in length, but the strawberry root weevil is only about one-quarter inch or less in length.

The notching caused by adult root weevils is often considered only cosmetic, not causing significant harm to the plant. However, a large population of root weevil larvae do injure and kill young woody plants by feeding on the roots and the bark of stems close to the soil.

If you want to manage a root weevil problem without traditional chemical pesticides, you can utilize several approaches:

– Go out after dark and hand pick the adults off the plants and drop them in a container of soapy water or try placing a white cloth beneath each plant and gently shaking the branches. The root weevils will drop onto the cloth.

-Trap root weevils by tying corrugated plastic or cardboard (with the grooves facing inward) around stakes and laying them in the garden. They will hide in the corrugation groves during the day. Open up the traps and dispose of the roots weevils regularly.

– In some areas, parasitic nematodes applied as a drench can be used to manage a root weevil problem, but they work best when applied to very wet soils in late summer or early fall. Experts are doubtful that success can be achieved with these nematodes in our region .

Earth-friendly bio-insecticides include Beauveria bassiana (an insect killing fungus), azadirachtin (an extract from the neem tree that disrupts insect feeding), and spinosad (a soil bacteria byproduct). Chemical pesticides that will work include acephate, cyfluthrin, bifenthrin, and malathion. If applying materials to food crops such as strawberries, be sure the crop is listed on the pesticide label. Not all materials mentioned here are safe and labeled for use on food crops.

To be effective, both bio-insecticides and chemical insecticides should be applied as a spray when new foliar notching is noticed when the adults first emerge in early summer. The weevils feed for three or four weeks after they emerge before they start laying eggs. Each BVW female can lay 200 to 500 eggs and all BVWs are female! Applying controls early in the season, will help reduce a potentially burgeoning population.

Published: 7/11/2009 9:06 AM

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