Flea Beetles

Flea beetle adults are from 0.06 to 0.12 inch (1.5­–3 mm) long. These insects derive their name from their well-developed hind legs; when disturbed they jump like fleas. Flea beetles can overwinter on weed hosts surrounding the field, on residues of a previous tomato crop, or in the soil if the previous crop was a flea beetle host.

Flea beetles are common pests of seedling tomatoes in most areas. Adult beetles chew small holes in leaves, giving them a sievelike appearance. The small, slender, white larvae feed on underground parts of the plant, but this damage is not economically significant. High populations of flea beetles feeding on plants younger than the 4- to 5-leaf stage can result in stand loss, especially under hot, windy springtime conditions when the injured plants are desiccated. Foliar damage to mature plants is not considered to be economically damaging.

On rare occasions, flea beetles may feed directly on ripe fruit, just below the calyx. This damage resembles feeding by young tomato fruitworm, Heliocoverpa zea, or by tomato pinworm, Keiferia lycopersicella, and is usually seen only in very late-season plantings where leaves are senescing as a result of maturity, lack of water, or powdery mildew. Damage to fruit has caused it to be rated offgrade.

Monitor seedling tomatoes for flea beetles, especially if the field was previously planted to tomatoes. A single treatment is generally adequate for damaging populations.

Research has shown that seedling damage is significantly higher in fields previously planted to tomatoes than to crops such as wheat or sunflowers. This indicates that an overwintering population might exist; if possible, rotate tomatoes with a nonhost crop. In fields not previously planted to tomatoes, flea beetle infestations are usually located at field borders. Replanting rows near borders that have been heavily damaged is an option.

Late-season fruit damage may be avoided by maintaining a healthy plant canopy.

Crop rotation with a nonhost crop to reduce resident fields populations and sprays of pyrethrin are organically acceptable methods for managing these pests.

Monitor fields for flea beetles soon after transplanting or after the plants emerge. Fields previously planted to tomatoes should be monitored carefully. Treat for flea beetles when small holes are observed on new transplants or on seedlings in seeded fields. In general, damage to seedlings is greater than to transplants. Young plants will often withstand flea beetle injury, but they may be killed if the weather is dry and windy. The percentage of plants affected and forecasted weather conditions will indicate the need to treat. Once established, plants can overcome moderate flea beetle feeding.

When the flea beetles on seedlings are migrating from hosts outside of the field, most of the infestation will be localized within 200 feet of borders. Check the distribution of plants that have evidence of leaf feeding to see if this is the case and consider border treatments only.

If high populations exist 1 to 2 weeks before harvest and foliage is declining as a food source for the beetles, spot-treat according to the distribution of the flea beetle.

Begin by monitoring the 5 rows adjacent to field edges and the first 25 feet at ends of rows. (No further sampling is needed if flea beetles are not present.) Look at leaves of 30 plants damaged by flea beetles. Expand the search area to delineate total area affected, if necessary.

Consider a spot treatment in rows that have 5-10% of seedlings or young plants with heavy flea beetle feeding. Once plants have more than 4 true leaves, treatment is not usually necessary.