Not all visitors to the garden are equally welcome. Among the least welcome of all is the cucumber beetle, a potentially devastating pest to the cucurbit family, including cucumbers, cantaloupe, honeydew, casaba melon, winter squash, pumpkins, summer squash and watermelon. Coincidentally, that is the order of preference shown by these insects in their feeding habits.
Several insects are referred to as cucumber beetles. The two primary pests likely to be found in our gardens are the western spotted cucumber beetle (Diabrotica undecimpunctata undecimpunctata) and the western striped cucumber beetle (Acalymma trivittatum). The spotted beetle looks very much like a greenish-yellow ladybug and is similar in size. Many neophyte gardeners mistake them for beneficial insects, rationalizing that such a "cute" bug couldn't be harmful. The striped beetle is about 1/4-inch long and yellow-green, with three distinct black stripes that extend from the head to the tip of the abdomen. Although not fierce looking, it can devastate a crop in a short amount of time.
Adults feed on the blossoms of as many as 200 host species, including hawthorns and dandelions, until cucumber, squash, or melon seedlings emerge or transplants are set out in fields. Because adult cucumber beetles are strong fliers and can be carried long distances — up to 500 miles in three or four days — by high-altitude air currents, they can disperse rapidly and travel widely during the summer. Very few gardens are safe from possible infestation. Even if not present in sufficient numbers to bother your plants this year, they may over-winter in garden debris, ready to come back in large numbers next year. Cucumber beetles may infect plants with bacterial wilt, which causes them to die. Larval feeding on roots and adult feeding on above-ground plant parts affect the growth and marketability of cucurbits and other crops. Cucumber beetles also transmit viral diseases, including the squash mosaic virus and various bean viruses.
Controlling beetles is not a simple matter. Chemical pesticides are commonly used in conventional vegetable production to control populations of cucumber beetles. If insecticides are used, they should not be applied during pollination to avoid harm to honey bees and other pollinators. Pesticides such as Adios® that combine cucurbitacins (the substance that makes cucumbers taste bitter) as a feeding stimulant with a small amount of the pesticide carbaryl (Sevin „¢) can be both effective and selective in controlling cucumber beetles.
Organic control centers around the principle of IPM, integrated pest management. The idea is to combine our knowledge of the pest's lifecycle, reproductive habits and preferences with timely, non-toxic measures to disrupt, interfere and confuse the insect into staying away from our crops. Add the use of organically approved sprays and predatory insects and the gardener can have quite an arsenal at their disposal to deal with these beetles.
The principles used against the beetles include:
- Population monitoring with yellow sticky traps to know when the adults make their first appearance
- Cultural practices like delayed planting, the use of row covers, heavy mulching and plant trellising to prevent egg laying
- Cultivation and residue removal to prevent the insect from making our garden its winter refuge
- Insect vacuuming, which is simply using strong suction to collect these insects directly from the plants on sunny mornings when they are most active
- Use of trap crops that are particularly attractive to cucumber beetles
- Trap baits and sticky traps are effective against adults that are actively seeking forage and egg-laying sites. u Natural predators, which include soldier beetles, tachinid flies (Celatoria diabroticae), braconid wasps, predatory nematodes that attack the larval stage, and bats. While usually not sufficient to control a large outbreak on their own, the natural predators are a helpful control measure when used with other methods.
- Botanical and biorational insecticides and protectants include pyrethrum or rotenone, which may be used in combination with the particle film barrier, Surround WP„¢ Crop Protectant. It is made of edible kaolin clay and disrupts insects by sight confusion.
By using a multi-pronged attack we can limit damage from these insects while enjoying a bountiful harvest free of highly toxic substances that may create more problems than they solve.
Stan Mapolski, aka The Rogue Gardener, can be heard from 9-10 a.m. Saturday mornings on KMED 1440 AM and seen in periodic gardening segments for KTVL Channel 10 News. Reach him at firstname.lastname@example.org.