Flea beetles on Plants

Symptoms

Adult beetles chew small holes in leaves, which gives the leaves a sievelike appearance. The adults feed on the underside of leaves, creating small pits or irregularly shaped holes. The small circular holes give leaves a shot-hole appearance, and you will see the same shot-hole damage on arugula and other Brassica leafy greens. Heavy feeding by adults can leave leaves bleached and pitted, or full of ragged holes. High numbers of adults can kill or stunt seedlings, which can be economically damaging.

Larvae cause a second kind of damage below ground, because they feed on roots, root hairs, stolons and tubers. On potato, larval feeding shows up as worm-track tunneling injury in the tubers. The tuber surface can look pimpled, with small brown tunnels, and small raised bumps may also appear on it. Larval attack can also leave rough skin, deep cracks and scab-like lesions on tubers. On carrots, larval feeding causes sunken spots on the roots.

Causes

Adult flea beetles overwinter in weeds or plant debris outside the field. In spring they fly into crops. Fields that are weedy, or surrounded by weeds, harbor adult beetles before they move into the crop. Flea beetles are most active in the spring-summer season, though they can occur any time.

Most of the damage is caused by larvae, which hatch from eggs laid in the soil around host plants. On potato, two generations per year allow populations to build. Seedling damage is significantly higher in fields previously planted to tomatoes. Tomato is a host as well, so it matters twice in this cycle.

Weeds and plant debris matter in two ways, since adults overwinter in them and weedy margins harbor adults before they move in. Long-distance spread has a different route, and commercial transport of infested potato tubers is the main pathway. The hosts on this page are potato, tomato, carrot, cabbage, broccoli, cauliflower and arugula.

Diagnosis

Start with the leaves. Adult feeding leaves small circular holes, or small pits and irregular holes on the underside of leaves. Holes chewed right through a leaf, giving it a sievelike look, point to adult beetles. Leaves that look bleached and pitted, or ragged, suggest heavy adult feeding. A seedling that dies or stays stunted is another sign of heavy adult feeding.

If the leaves look fine, look at the roots and tubers for larval feeding. Larvae feed on roots, root hairs, stolons and tubers. Tubers with small brown tunnels, worm tracks, rough skin or scab-like lesions fit larval attack. Sunken spots on carrot roots fit larval feeding as well.

Season and surroundings give more clues. Flea beetles are most active in spring and summer, and weedy fields or weedy margins harbor adults. Your crop history is a clue as well, since seedling damage is significantly higher in fields previously planted to tomatoes. Check seedlings and new transplants for damage twice a week until plants are well established. White sticky traps can also be used to monitor adult flea beetles.

Treatments

Remove weeds along field margins to keep adult flea beetles from moving into the crop. Remove plant debris in the fall to eliminate overwintering sites for adult beetles. Protect seedlings with protective coverings until they reach a later leaf stage, when they can tolerate feeding. Row cover over susceptible crops such as arugula matters, since unmanaged infestations can devastate plantings without it.

Apply reflective mulches soon after planting and before plants become infested. Rotate host crops such as tomato with a nonhost crop to reduce overwintering populations building up on-site. For potato, destroy overwintering sites and rotate with non-solanaceous crops over a multi-year cycle. Wash or brush seed potatoes so they are free of plant debris before planting.

Monitor fields visually for adults beginning at a set point in crop emergence. Targeting insecticide applications on counts substantially reduces the spraying needed. Limit insecticide use to infested areas. White sticky traps can monitor or trap adults.

The product label is the legal instruction and must be followed for the crop and site being treated. Insecticidal soap sprayed at the cotyledon stage gives partial control of flea beetles on cole crops. Pyrethrin, an organically acceptable option, can be sprayed to manage flea beetles on tomato.

Sulfur-containing pesticides may act as a repellent against flea beetles. Carbaryl is sprayed where infestations are serious on home garden plants or on cole crops registered for this use. Imidacloprid on cole crops is effective against the root-feeding larvae only, and it is also used on potato. Thiamethoxam is used on cole crops, and its metabolites include a neonicotinoid highly toxic to bees. On cole crops, dinotefuran remains highly toxic to bees for an extended period after application. Clothianidin on tomato is a foliar spray, and it should not be applied during bloom or when bees are actively foraging. On tomato, esfenvalerate and lambda-cyhalothrin are restricted to late season if fruit feeding is a concern.

Prevention

Keep field margins free of weeds, since weedy margins harbor adult beetles before they move into the crop. Clear plant debris in the fall to remove overwintering sites. Rotating a host crop such as tomato with a nonhost crop lowers the overwintering populations that build up on-site. Potato follows the same idea, with non-solanaceous crops in a multi-year cycle.

Brush or wash seed potatoes free of plant debris before planting. Cover seedlings until they reach a later leaf stage, when they tolerate feeding. Put reflective mulch down soon after planting, before plants become infested.

Timing matters for highly susceptible crops like arugula. Flea beetles are most active in the spring-summer season, so avoid growing arugula outdoors then, or use row cover. Check new seedlings and transplants twice a week until they are well established.

Plants most often affected

Flea beetles affect potato, tomato, carrot, cabbage, broccoli, cauliflower and arugula. Arugula and other Brassica leafy greens show shot-hole damage on the leaves. Potato tubers show worm-track tunneling injury, and carrot roots show sunken spots from larval feeding.

• Aji
• Cayenne Pepper
• Common Beet
• Crepe Myrtle
• Eggplant
• Field Pumpkin
• Garden Cucumber
• Garden Tomato
• Parsley
• Rocketsalad
• Spinach