Rid organically bugs, beetles, bores, and caterpillars that are bugging gardeners this summer

By Dorothy Pellett

 

A While it might be tempting to get rid of all of them, a closer look reveals that many bugs are beneficial, as natural predators of garden pests or as pollinators and honey producers. Gardeners, then, are seeking ecologically sound ways to control specific pests that threaten to eat, defoliate or discolor their flowers and vegetables. For many people, a goal of keeping pesticides out of waterways and sparing beneficial insects means that they will use more hands-on controls and learn about the effects of products they apply.

Cabbageworms, Japanese beetles, striped cucumber beetles, squash bugs and lily leaf beetles are attracting attention now, particularly Japanese beetles that appeared to descend overnight by the hundreds into some homeowners' yards.

Cabbageworms

Small white butterflies hovering over vegetable crops in the cabbage family are a sign that the imported cabbageworm larvae (caterpillars) soon will begin to devour the crop unless the gardener intervenes. Fortunately, this pest is one of the easiest to control.

Robert and Sonja of Charlotte raise almost all of their vegetables for year-round use, including broccoli, cauliflower, Brussels sprouts, kale and cabbage -- all cabbage relatives. "When we start seeing the white butterflies, it's time to spray with Bt once a week," they said. Bt is the common name for Bacillus thuringiensis, a bacterium that occurs naturally in soil and that is used in preparation of the insecticide. When the cabbageworm and cabbage looper caterpillars ingest Bt, their digestive tract is paralyzed, and they die. Other strains of Bt are available for potato beetle larvae and for mosquitoes; it's important to read the label and purchase the right one for the pest you want to remove.

The caterpillar strain (Bt variety kurstaki) is considered safe for use on vegetables up to the day of harvest. Cheryl Bruce, with the certification staff of Vermont Organic Farmers, said, "Bt is a great option for home gardeners to use instead of a synthetic chemical. Some Bt products, like Dipel, are approved for use on certified organic farms. Others are not because of the ingredients used with Bt." Japanese beetles

Japanese beetles can quickly skeletonize leaves of roses, grape vines, raspberries and linden trees -- apparently some of the most tasty food for the beetles. They are the adult form of white grubs that feed on grass roots in lawns, so control of beetles is closely tied to treatment for grubs.

"There is no simple solution to the Japanese beetle problem," said Margaret Skinner, research associate professor of entomology at the University of Vermont. "It is yet another example of the impact of exotic invasive insect pests."

Adult beetles crawl into the soil each evening and lay eggs. When eggs hatch into white grubs that disfigure lawns by eating roots, their predators add to the damage. "In some years, many of Burlington's lawns are torn up by skunks and raccoons foraging for grubs, leaving large areas of dead grass," Skinner said.

Biological products such as nematodes and milky disease (a disease of grubs also known as milky spore disease) are recommended in some areas of the United States. Skinner said, "Biological control is not likely to provide the immediate results that most homeowners seek when trying to manage Japanese beetle." Milky spore disease would require more than two years to spread throughout a lawn, she said, and our climate could be too cold for it to be effective.

Skinner said several commercial insecticides are registered for use on Japanese beetles. Gardeners suggest vacuuming the beetles off plants or hand-picking them to be dropped into a jar of detergent solution or simply squashing them, for the non-squeamish among us.

After finding a large population of Japanese beetles on a friend's grape vine, we checked with Shelburne Vineyard owner Kenneth Albert to learn his strategy. "We are an organic vineyard, and we just live with them until they go away," he said.

Albert said the beetles feed for a few weeks, then are gone. "They may hit one section of the vineyard and not another. When grapevines are young, they are most susceptible, but in subsequent years if a few leaves are lost, others grow quickly to replace them. You can almost watch the vines grow," he said.

Homeowners with a small number of plants might protect them with a light row-cover material, Skinner said. Summerweight covers of spunbonded polypropylene are available at local garden supply stores.

The beetles are easy to identify by their metallic green color combined with a coppery hue on the wing covers. But Skinner said two other related beetles sometimes are confused with them. "People think they have Japanese beetles, but they really are seeing Asiatic garden beetles or Oriental beetles," she said. Reddish-brown is the color of Asiatic garden beetles; Oriental beetles are lighter brown with a few variable black spots. All three are garden pests and can be treated similarly, but the Asiatic and Oriental beetles usually feed at night, while Japanese beetles feed in the daylight and burrow into soil at night. Other pests

Squash bugs are candidates for handpicking of adult bugs and squashing of egg masses on the undersides of leaves, a technique used by the Ullriches also for potato beetles. Quarter-inch-long striped cucumber beetles, however, usually require different methods. Skinner recommended a rotenone insecticide, applied while wearing gloves and a mask.

Brilliant red lily leaf beetles are relatively new pests in Vermont. State plant pathologist Tim Schmalz said gardeners should watch lily plants for the beetles and the larvae that resemble small yellowish-brown rough-textured slugs. "They should be aware of them when they are sharing lilies," he said. Lily leaf beetles do not feed on daylilies; Asiatic lilies (bearing leaves along the stem) are examples of true lilies that could host the beetles.

The larvae can be picked off, and products containing the botanical insecticide Neem that will help to keep the beetles from spreading.

Before purchasing or using an insecticide, gardeners should study its label for safe practices and use on specific plants.


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