Cucumber beetles: how to recognise and treat it

Pest

Symptoms

Yellow beetles about 6–7 mm long with three black stripes (striped cucumber beetle) or yellow-green with 12 black spots (spotted cucumber beetle) on seedlings, leaves, flowers and fruit.
Chewed cotyledons, leaves and stems of young plants; scarred fruit rind on older plants.
Vines suddenly wilt and die even though the soil is moist — bacterial wilt spread by the beetles; cucumbers and melons are the most susceptible, watermelon is not.

Cover seedlings and transplants with row covers right after planting and remove them when flowering starts so bees can pollinate.
Spray kaolin clay as soon as seedlings emerge, before the beetles arrive, and repeat after heavy rain; it repels the beetles but does not kill them.
Surround the bed with a strongly attractive trap crop such as Blue Hubbard squash and kill the beetles that gather on it.
Check plants at least twice a week from emergence; beetles are hard to hand-pick because they fly off or drop to the ground.

Pyrethrins or neem (azadirachtin) labelled for cucumber beetles; pyrethrins give a short knock-down with no residual effect, so spray in the evening, when the beetles are active and bees are not.
A pyrethroid such as lambda-cyhalothrin, where approved, only before flowering because it is highly toxic to bees; follow the label dose and pre-harvest interval.

Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.

Grow cucurbits as far as possible from last year's patch; moving them within the same bed does not help, as the beetles are mobile.
Protect plants most carefully from emergence to the five-leaf stage, when bacterial wilt does most harm.
Mulch established plants with straw, leaves or grass clippings.
After harvest, destroy or bury vines and leftover fruit, where the adults overwinter.

Figures checked against these sources.