Cucumber Beetles

Cucumber beetles (Diabrotica spp.- spotted and striped):
Order: Coleoptera Family: Chrysomelidae

For cucumber beetles: 1600 X-clude Formula 2, Pyrethrum Insecticide

These bugs  have yellowish-green colored bodies with black spots or stripes, a black head and are 1/4 inch in length. Eggs are oval in shape, yellowish-orange and laid in the soil nest to host plants. The larvae are 1/4 to 1/2 inch long, with a beige to white body, brown head, brown spot on the tail end. Larvae attack plant roots and stems generally in spring for 2 to 6 weeks. The larvae and adults attack asparagus, broad beans, eggplants, potatoes, certain fruit trees, tomatoes, peas, squash, corn (a favorite), cucumbers, potatoes, fruits, and melons. This is not the limit as they will attack over 270 plants in 29 families including flowers and ornamentals! The adults transmit bacterial mosaic and wilts. These bacterial diseases actually overwinters in the beetles' intestines! When they are actively feeding again they transmit the diseases from plant to plant.  Symptoms of these diseases are wilting and death of plants. In spring the adults will feed enmass on seedling shoots and leaves. You will see adults feeding mostly on flowering plant flowering parts and pollen during summer. In fall they turn to the upper portions of plants and will also feed on weeds and trees. They infect some stone fruits with brown rot. The striped adults do the most damage to the cucurbit family.

Generally there will be one generation per season in colder areas and two to three in more southern climates. They become active early in the spring when temperatures begin to go above 50°F. Spotted cucumber beetles do not overwinter in northern areas but migrate in from southern states each year, arriving around June. In the southern states, spotted cucumber beetles emerge two to four weeks after the striped cucumber beetle.

Heavy infestations of the larva on corn will destroy the roots resulting in plants falling over. Root feeding may give the appearance of drought stressed plants. Adults will burrow into the corn ear tips. This in turn will result in discoloration and rotting of the corn. They also chew back the corn silks when pollination is to occur resulting in very poor grain set. As we previously mentioned this damage is hardly limited to corn. Cuke beetles are a serious pest indeed.

Cornell plant pathologists recommend scouting plants twice a week, especially when plants have less than five leaves. Since cucumber beetles like shade, examine the undersides of cotyledons, young leaves, and stems. Monitoring should involve the inspection of five plants (only one per hill) at each of five sites in a field, paying particular attention to field edges. Use these counts to calculate the average number of beetles per plant.

Thresholds for use of botanical or chemical control measures vary depending on species susceptibility to bacterial wilt. Cucumbers and cantaloupe are susceptible to bacterial wilt and should be treated within 24 hours if plants along the edges are heavily damaged or have 5 or more beetles per plant. Following the first treatment, apply follow-up treatments only if there is at least one beetle per plant.

Predators: Tachnid flies, soldier beetles, parasitic nematodes and braconid wasps. Lacewings and ladybugs eat the eggs.

Repellent plants: Broccoli, calendula, catnip, goldenrod, nasturtiums, radish, rue and tansy. If you want to try marigolds to repel them use the more pungent varieties like African, French or Mexican marigolds. The more common marigolds may actually attract them, therefore could be used as a trap crop.

Control Methods:

• Use a portable vacuum to get the adults in the early evening. Put them right into a plastic bag, seal it and dispose of them.
• Try placing cuttings of the tansy plant as a mulch in-between rows in the garden.
• Spread any type of onion skins on the soil around the planted areas.
• Consider building a bat habitat: Bats are predators of a wide range of pest insects, including cucumber beetles.
• Make a trench 3" deep by 3"  wide filling it with wood ashes. Moisten it so it won't blow away and don't let it get on the plants. Ashes can be toxic to plant foliage!
• A deep mulch of straw helps by keeping the adults from walking plant to plant. Heavy mulching can deter cucumber beetles from laying eggs in the ground near plant stems and may hinder feeding by larvae migrating to fruits. This cultural control method, however, does not protect the leaves against attack from adult insects. Injury to fruit by tunneling of larvae is dependent on very moist soil as fruits ripen. Limiting irrigation at this time can minimize damage
• Plant white varieties of radishes or rattail radishes with your cucumber plants to repel the beetles. Rattail radish roots are not edible but the seed pods are!
• Mix a spray of 1 ounce wood ashes, 1 ounce hydrated lime and 1 gallon water. Spray upper and lower leaf surfaces. Hydrated lime is a powdered substance. Or use a spray of hot peppers, water and garlic.
• Trellising plants can make leaves less accessible to insect larvae and may decrease egg-laying. Like mulching, trellising does not protect plants against attack by adult insects
• Plant radish seeds right in the hills with the cucumber plants.
• Floating row covers are an effective control method during the early season of plant growth. They prevent insect attack by forming a barrier between insects and plants. Row covers need to be removed during the late vegetative stage, at the onset of flowering, to allow for bee pollination. Once floating row covers are removed, other control measures such as treatments with botanical pesticides should be employed.
• To fool cuke beetles: flatten a square of aluminum foil around the base of plants to bounce light on the undersides of leaves. This also helps the plants in giving them more light.
• Plant any type of beans with cucumber.
• Cultivate in the fall to expose the eggs.
• If the infestation is beyond control use either of the botanical poisons: pyrethrum or rotenone. You want to hit the adults with these when you observe them feeding on pollen in flowers.
• Sticky Traps: For the home gardener and small scale growers these can be an effective monitoring tool and a control! Cut some plywood board into rectangles 8 inches by 10 inches. Cardboard could also be used. Paint with yellow paint and coat with Tanglefoot or some other adhesive. Now what you want to do is to bait these traps specifically to trap cuke beetles. You can use pieces of cotton wicks stuck to the boards that have been soaked in a Eugenol based oil which is what attracts the female beetles. 2 types of oils that contain 60 to 90 percent eugenol are allspice oil and clove oil. Squash blossoms contain indole which are very attractive to the adults. If you can spare some you might mash them up and stick them to your trap. Stake your traps vertically at ground level or no more than 12 inches above. As the traps fill up you can scrape and recoat them until they become unusable.
• Nematodes: Hexamermis spp. parasitizes the adults. Studies have indicated up to 90%  of a population of cuke beetles being infected by the nematodes. Apply beneficial nematodes to kill the adults in mulch, seed furrows and around plant roots.
• Neem Oil: Neem oil, which can act as an ovicide, can be used as a soil drench to treat eggs and larvae. It does seem to help with control of the adults as a repellant and antifeedant. Further tests must be done using Neem but it does look promising.

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Update: 07/15/11