There are two cucumber beetle species; the striped cucumber beetle (Acalymma vittatum) and the spotted cucumber beetle (Diabrotica undecimpunctata howardi).
Both species feed primarily on the leaves, flowers and fruits of cucurbits (cucumbers, squash, pumpkins and melons). Alternate plant hosts include beans, corn, peanuts and potatoes.
Differences between striped and spotted cucumber beetles
Spotted cucumber beetles feed on over 200 different crop and non-crop plants, whereas striped cucumber beetles have a much stronger preference for cucurbits and rarely feed on other plants. Striped cucumber beetles lay eggs at the base of cucurbit plants and their larvae then feed on the roots of these plants.
The spotted cucumber beetle is very different, primarily laying its eggs on corn and other grasses such that the larvae of spotted cucumber beetles are not damaging to cucurbit crops. Once the eggs hatch, the larvae spend several weeks feeding on root tissue.
Thus, damage by the larvae might not be obvious just from looking at aboveground foliage—unless one attempts to pull up a plant and finds little resistance due to roots having been eaten. Larvae then pupate in the soil for about a week before emerging as adult beetles.
The striped cucumber beetle is either yellowish-green or orangeish-green with three black stripes down its back while the spotted cucumber beetle is also either yellowish-green or orangeish-green with 12 black spots on its back.
Both pests are about 1/4 inch long.
Cucumber beetles are a major concern and can cause serious losses. They also vector diseases.
While the adults feed mainly on foliage, pollen and flowers, their feeding on melon rinds late in the season may reduce market quality.
LIFE CYCLE
Cucumber beetles overwinter as adults in protected areas in plant debris, in fence rows, or in wood lots. They become active when temperatures begin to increase.
The adults feed and females deposit eggs in cracks in the soil at the base of cucurbits, which hatch in several days and the larvae feed on the plant roots and underground parts of the stem. Pupation takes place in the soil, and the next generation of beetles emerges.
It takes about 40 to 60 days for this insect to go from an egg to an adult.
DAMAGE
Cucumber beetles eat the leaves, flowers and fruit of the host plants and their larvae feed on roots and underground portions of the stems. If populations are high, the beetles feed on the stems of the plants as well.
Generally, these beetles damage cucurbit crops in at least three ways.
- Their feeding directly stunts plants and, when flowers are eaten, this reduces fruit set.
- The cucumber beetles transmit diseases like mosaics and bacterial wilt (Erwinia tracheiphila).
- The adults scar the fruit reducing its marketability.
It is primarily young cucurbit plants that are vulnerable to stunting and bacterial wilt disease, whereas damage to older plants primarily comes from fruit scarring.
MANAGEMENT STRATEGIES
Chemical method
The following insecticides re recommended for use against cucumber beetles;
- KINGCODE ELITE 50EC 10ml/20l
- LEXUS 247SC 8ml/20l
- SINOPHATE 750SP 20g/20l
- EPITOME ELITE 500SP 10g/20l
- PRESENTO 200SP 5/20l
- PROFILE 440EC 30ml/20l
- PENTAGON 50EC 10ml/20l
Non-chemical control methods
- Use yellow sticky traps to catch cucumber beetles.
- Knock beetles to the ground and catch them with a piece of cardboard placed under the plant. Or, use a handheld vacuum to suck up the beetles. They are very hard to hand pick, but it is easier to hand pick them with yellow gloves coated in petroleum jelly.
- Cover seedlings with row covers, though they must be removed during blossoming time several hours each day to allow for pollination.
- Select resistant varieties whenever possible
- Use of commercially available beneficial insects, such as ladybugs, green lacewing and the spined soldier bug, which feed on pest eggs.
- Use of beneficial nematodes work well to curtail immature stages developing in the soil.
- Remove garden trash and other debris shortly after harvest to reduce overwintering sites.
- Rotations with non-host crops
- Proper weed control (weeds harbour pests)
- Planting resistant/tolerant varieties
Note;
- Whenever spraying any insecticide, it is advisable to mix it with INTEGRA 3ml/20l. This is a sticker, spreader and penetrant which improves the efficacy of the product.
- To avoid resistance build-up by the pest, several insecticides should be alternated throughout the crop season.
- Timely control of the beetles is very critical.
