|Cucumber beetles (Diabrotica spp.-
spotted and striped):
Order: Coleoptera Family: Chrysomelidae
For cucumber beetles: 1600
X-clude Formula 2,
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
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
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.
- 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
- 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
- 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
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