Cucumber beetles are found throughout the United States. The 2 major types of cucumber beetles that may attack your garden are: Striped cucumber beetle (Acalymma vittatum) and Spotted cucumber beetle (Diabrotica undecimpunctata).
The adult striped cucumber beetle has a yellow body sporting 3 black stripes down the back on its wing covers. Striped cucumber beetles have black abdomens below and pale colored legs with black “knees” and their stripes are distinct and extend to the tip of the wing.
The adult spotted cucumber beetle has a yellowish-green body with 12 black spots on its wing covers. Both beetles are similarly sized at about ¼ inch long with the spotted cucumber beetles being somewhat larger on average. Both beetles have black heads.
Eggs are yellowish-orange in color and are laid on the stems or in the immediate vicinity of the stem of a viable host plant. The larvae of both beetles are between ¼ to ¾ inch long slender white to yellowish-white grubs with brown heads. Larvae feed on roots and stems for 2-4 week, then pupate and emerge as adults in another 2 weeks.
Cucumber beetles have a wide range of host plants making them an utter nuisance. Both adults and larvae feed on cucumbers and related plants, including melons, winter and summer squash and gourds. They may also atta
ck asparagus, beans, beets, eggplants, potatoes, certain fruit trees, tomatoes, peas, pumpkins, peppers, corn, cotton and soybeans.
Cucumber beetles infestations damage crops in at least 3 ways. First, their direct feeding on infested crops directly stunts plant growth and affects yield. The adults feed on leaves, young shoots, flowers and stems and can even damage mature fruit. Second, cucumber beetle larvae feed on host plant’s roots. They tunnel into roots, often stunting growth, especially seedlings. Third, cucumber beetles may transmit bacterial wilt disease (Erwinia tracheiphila) which is an incurable and often fatal disease. The bacteria passes from the frass (excreta) of the beetle into feeding wounds that reach into the vascular tissues of the plants, where they proliferate to the point of blocking the xylem, causing the plant to die off. Cucumber beetles may also carry viruses such as squash mosaic virus and cucumber mosaic virus.
Organic Control and Prevention of Cucumber Beetles:
1. Row covers: Protect young seedlings from cucumber beetles by covering with floating row covers, individual screens or cones. Remove row covers at the onset of flowering for adequate pollination.
2. Mulching: Use straw, hay, plastic, fabric or paper as mulch to deter cucumber beetles from laying eggs in the ground near the plants. Mulching may not stop egg-laying or feeding but it will limit direct access to the stem and roots. Using reflective metallic-colored mulches help repel flying cucumber beetles.
3. Cultural practices: Since cucumber beetles may overwinter in your soil and in crop residues both above and below the ground, it is necessary to practice clean and thorough cultivation after fall harvests. Deep tillage, compost application and removal of crop debris should be practiced to minimize pest attacks. Practice crop rotation, i.e. plant your crops in different locations every season.
4. Monitoring and handpicking: Scout your crops regularly for sign of cucumber beetles and their eggs. Use a vacuum to get to adults in the early evening and dispose of them.
5. Physical traps: Sticky yellow traps help capture cucumber beetles as they are attracted to yellow like most insects. For added effect, attach a cotton swab dipped in the oil of clove, cinnamon, cassia or bay leaf, all of which act as attractants.
6. Kaolin clay: Apply kaolin clay to young plants, especially to leaf undersides which acts as a sticky barrier to those hungry cucumber beetles.
7. Delayed planting: If your season permits or even if it doesn’t, delay the planting of your crops by a few weeks to avoid the early spring cucumber beetle migration. This can be done by starting seedlings indoors and then transplanting them into your garden at the opportune moment.
8. Trap crops: Like us, cucumber beetles have preferences of food. Plant trap crops along the perimeter of your garden and about 1-2 weeks earlier than main crop. Recent research indicates that the Blue Hubbard and buttercup varieties of Cucurbita maxima, zucchini and ‘Big Max’ pumpkin are particularly attractive to cucumber beetles.
9. Companion planting: Radish, nasturtium, tansy, buckwheat, cowpea or sweet clover planted with your main cucurbit crop can help reduce cucumber beetle numbers.
10. Neem oil: Neem oil, which can act as an ovicide, can be used to drench the soil to kill eggs and larvae. It also seems to help as a repellant and anti-feedant in the control of adult cucumber beetles making it a good organic choice.
11. Beneficial nematodes: Parasitic nematodes can be bought and applied directly to the soil. They kill larvae dwelling in the soil.
12. Predatory insects: Braconid wasps, tachinid flies, hunting spiders, web-weaving spiders, soldier beetles, carabid ground beetles and bats can help control cucumber beetle populations and their presence should be encouraged by planting flowering plants.