Pale-Striped Flea Beetle

Flea beetle adults are small (about 0.12 inch), shiny beetles with enlarged hind legs that allow them to jump like fleas. The pale-striped flea beetle has a broad white stripe down each brown wing. Flea beetles can overwinter on weed hosts surrounding fields and in soil and plant residues of previous susceptible crops such as tomatoes and other fruit and vegetable field crops.

Adult flea beetles do most of the damage by feeding on the undersides of leaves, leaving small pits or irregularly shaped holes on the leaves. Large numbers of flea beetles can kill or stunt seedlings. Older plants rarely suffer economic damage although their older leaves may be damaged. The small, slender, white flea beetle larvae feed on underground parts of the plant, but this damage is not economically significant. Outbreaks of flea beetles in alfalfa seedling fields have occurred in the Central Valley in the fall, but these beetles are also active during springtime.

Adult flea beetles overwinter in plant debris. To destroy possible refuge sites of adult flea beetles, maintain field sanitation by keeping field margins free from weeds. In case of infested fields, deeply disc plant residue after harvest. Crop rotation with nonhost plants (e.g., cereal grains such as wheat) and maintaining good plant health (e.g., no water stress) are also important for managing flea beetles in alfalfa production.

Only cultural controls are available for this pest on organically grown alfalfa.

Check newly emerged seedlings weekly for flea beetle damage until plants are well established, especially if there was a flea beetle problem in the previous crop. Sometimes infestations can be spotty, for example on field edges when they migrate into alfalfa stands. Relatively low numbers can cause economic damage when plants are in the cotyledon or first-leaf stages. Treat if you find that the flea beetles are causing stand loss. Alfalfa seedling fields need at least 10 to 20 plants per square foot to ensure a viable stand at the end of the first year of production.

Once plants have several true leaves, they can tolerate several beetles per plant without damage. Older plants are even more tolerant. Insecticide applications should rarely be required, but if it is, one application should suffice. However, insecticides may disrupt biological control of aphids, which are increasingly becoming a problem in alfalfa production. Spot treatment of infested areas may be warranted where stand loss is occurring in certain areas of the field, for example on field edges.