Controlling and Preventing Flea Beetles
If most leaves have already been munched on, pyrethrin spray or dust may be the best solution. As always, read and follow label directions and exercise safety in application and storage. Drape young plants with row covers and add parasitic nematodes to combat any larvae overwintering in the soil.
Leaves Have Large, Ragged Holes?
If leaves are completely missing or have large, ragged holes, then Colorado potato (CPB) or Blister Beetles (BB) may be the culprits. CPB adults are 1/3" long, have oval, yellowish hard shells with black racing stripes while their larvae are dark orange, humpbacked grubs with black spots. They leave their orange eggs clinging to the underside of the leaves. BB adults are 3/4" long, thin-bodied, metallic black, blue, purple or brown and are highly mobile so they may not be present when damage is noticed.
Controlling and Preventing Colorado Potato and Blister Beetles
Handpick the CPB adults, drown them and add to the compost pile. Wear gloves to handpick BB as their name implies, these beetles secrete a toxic substance, Cantharidin, which at the very least, causes skin irritation. Squash all eggs. If larvae are present, spray the plants with Bacillus thuringiensis, variety san diego. Cover young seedlings with row cover to exclude beetles and mulch with loose straw.
Blister Beetles and their effect on Livestock
All about Potato Beetles
Organic Control Options for the Flea Beetle