Flea Beetles

Description

Flea beetles are an early-season pest commonly found on all members of the cole crop group, as well as spinach, beets, potatoes, and eggplant. There are several different species of flea beetle that pose problems early in the season when they are considered occasional pests. Host plants of many of the flea beetles are easily identified by their common names. For example, the crucifer flea beetle attacks cole crops and mustards while the eggplant flea beetle is commonly associated with eggplant.

Common Wisconsin flea beetle species

Common Wisconsin flea beetles include the crucifer, eggplant, horseradish, pale-striped, potato, spinach, and striped varieties. All have characteristically large hind legs that give adults the ability to jump. Adult flea beetles range in size from about 1/10 – 1/5 inch. Larvae are delicate and thread-like with white bodies and brown heads.

Common name	Scientific name	Description	Host plants
Crucifer flea beetle	Phyllotreta cruciferae	greenish or bluish-black; 1/16″ to 1/8″	cabbage and other crucifers including horseradish
Eggplant flea beetle	Epitrix fuscula	black; 1/16″	eggplant
Horseradish flea beetle	Phyllotreta armoraciae	black with yellow stripes; 1/8″	horseradish and other mustards
Pale-striped flea beetle	Systena blanda	dark brown with 2 broad white stripes down its back; 1/6″	potatoes, tomato, eggplant, pepper
Potato flea beetle	Epitrix cucumeris	dull black; 1/16″	potatoes, tomato, eggplant, pepper
Spinach flea beetle	Disonycha xanthomeles	greenish-black with a yellow thorax; 1/5″	spinach and beets
Striped flea beetle	Phyllotreta striolata	black with 2 crooked yellow strips running down its back; 1/12″	cabbage

Symptoms and effects

Adults feed on both leaf surfaces, but usually on the underside where they chew small, circular holes through to the upper cuticle. This cuticle often remains in place for some time before trying and falling out. The circular holes give the plant a “shot-gun” appearance. Heavy feeding on young plants may reduce yields or even kill plants in severe cases. Crops grown for their foliage such as kale, bok choy, spinach, or mustards may be rendered unmarketable by flea beetle damage. Larvae feed on the roots and tubers of susceptible plants but don’t often cause economic damage. Larvae of the horseradish flea beetle also mine the stem and leaf veins. In addition, many are vectors of plant pathogens.

Life cycle

Flea beetles overwinter as adults in the soil or beneath plant debris. They become active in early spring when temperatures reach 50°F, and begin feeding on weeds or early-planted crops. Adults lay eggs in the soil at the base of host plants in May. Eggs hatch in 7-14 days and larvae feed on various plant parts until fully grown. They pupate in earthen cells for 11-13 days before emerging as adults. Adult flea beetles are particularly active on warm, calm, sunny days. Depending upon the species, there may be 1-3 generations per year.

Management

Scouting

Flea beetle populations can be monitored with yellow sticky traps. The number of beetles found in traps corresponds to the amount of feeding damage occurring nearby. Scouting for damage should occur every 1-2 days in newly planted fields, because flea beetles can quickly become a problem for young plants.

Cultural control

Adjusting planting dates to avoid damage caused by flea beetles may be useful. Floating row covers can prevent adults from feeding on leaves and laying eggs on the crop. If used, row covers should be set up just before the crop emerges. Water deters adult flea beetles, and any watering should be done in mid-day. Since flea beetles overwinter near fields, planting after adults have emerged or rotating crops can help minimize flea beetle damage. Commercially available nematodes that feed on flea beetle eggs, larvae, and pupae are available.

Chemical control

This option is recommended when flea beetle populations exceed threshold levels, particularly early in the season (see table). Soil-applied insecticides will provide season long control. Foliar insecticides can provide quick control but may also disrupt natural enemies of other pests of cole crops.

Action thresholds

Crop	Threshold
Beets	Treat when beetles cause stand reduction on small plants
Cole crops	Undetermined
Eggplant	<3″ = 2 beetles/plant 3-6″ = 4 beetles/plant >6″ = 8 beetles/plant
Horseradish	Treat only if beetles are found in high numbers early in the season
Potato	>2 beetles/sweep
Tomato	>2 beetles/plant

Refer to the UW-Extension publication Commercial Vegetable Production in Wisconsin (A3422) for an updated list of registered insecticides and management recommendations.