Problem type: Insect
Name of problem: Flea Beetle
Plant name(s): Vegetable crops; Occasionally flowers, shrubs and trees
Symptoms / Characteristics:
Flea beetles produce small holes that create a characteristic shot hole appearance in leaves. Plant stems, buds, seedpods and roots can also be fed on. Adult beetles feed on leaf surfaces producing small holes. The adult beetle is what is commonly seen as the other life cycle stages develop in the soil. There are many species of flea beetles, varying in color and size. The most common adults seen are small, shiny, black beetles, typically oval in shape and measuring around 3 mm long.
The name flea beetle is given to many species of beetles that jump when disturbed. Adult beetles generally walk or hop from plant to plant, but when the weather is calm, they may fly to new host plants. Invasion can seem to just appear from nowhere. All species have only one generation per year. Adults overwinter in plant debris near the soil surface. As temperatures warm in the spring, adult beetles will become active. Adults mate and lay eggs generally between late May and late June. Eggs are laid in the soil, hatching about 2 weeks later. The larvae then feed on plant roots, remaining in the soil to pupate. Larval feeding normally does not cause a lot of damage. Adults emerge from the soil as beetles around mid July until September. The beetles then begin to feed on leaves, stems and seed pods. By late August to late September, adults search for a place to over winter in leaf litter and debris.
Control / Preventions:
Flea beetle damage is usually not detrimental to plant health if the plant is already established. Most damage occurs on seedlings in the spring when they are young and most vulnerable. By encouraging seeds and seedlings to grow quickly, they may be able to overcome injury. Plant transplants or seeds when temperatures are warmer to help plants establish quickly and combat flea beetle feeding. Injury can also be avoided by planting during periods of low flea beetle activity.
In fall, remove leaf litter and other debris to reduce overwintering sites for adult beetles. Crop rotation does not control flea beetles as beetles may overwinter over large areas and are able to travel far distances to feed.
For field crops that are of value, chemical seed treatments can be used to protect young seedlings while they are establishing. Treatments involve coating seeds with an insecticide as well as a fungicide before planting. This will protect the plants as soon as they emerge.
Monitor plants in the fall for adult beetles and decide whether they are abundant enough for control. The number of adults in the fall will give an idea of potential problems next spring. Adult beetles can be controlled by a number of products. As soon as adults are noticed in either the spring or fall, an insecticide can be applied. Sevin can be used, but may need repeated applications for effective control. Horticultural oils can be used as a spray or diatomaceous earth applied as a dust on the leaves of plants will also provide control.