Flea beetles may take small bites, but they can add up to big problems. Their feeding on the leaves of solanaceous crops like eggplant, peppers, and tomato can delay the establishment of seedlings or even kill them. The same is true for brassica crops, like cabbage and kale, with the additional concern that damage to foliage reduces marketability, even if it doesn’t affect yield. And, flea beetles don’t just attack leaves; in their larval stage they feed on roots, too.
Some species of flea beetles, like the corn flea beetle, will attack many different crops, but most species prefer a small group of related plants. On vegetable farms in the Northeast, one can find the horseradish flea beetle, potato flea beetle, and spinach flea beetle, to name a few. Some of the most problematic flea beetles are two that attack or brassicas, or crucifers: the crucifer flea beetle, which is all black, and the striped flea beetle, which is black with two light tan stripes on its back.
Life Cycle. Flea beetles overwinter as adults under soil and leaf litter in brushy or woody areas surrounding fields, rather than in grassy areas right next to fields. They emerge in early spring when temperatures reach about 50 degrees, feeding on weeds or crops, if available. Females soon lay their eggs in the soil at the base of these plants. Eggs hatch in a week or two and the larvae feed on plants until fully grown. Then they pupate in the soil for 11 to 13 days before emerging as adults. Delaying the planting dates of susceptible crops until after the overwintering beetles have emerged is one way to reduce damage to young plants.
Preferences. On common brassica vegetable crops of European origin, such as broccoli, Brussels sprouts, cabbage, cauliflower, collards, and kale, the first leaves to emerge on these crops are very attractive to flea beetles, but as the plants grow and the leaves become waxier it is difficult for beetles to grasp and feed on them. So, once seedlings have grown beyond the two- or three-leaf stage, flea beetles tend to be less of a threat.
Some brassica crops, especially those of Asian origin, have non-waxy leaves, which are easier for beetles to get a hold of and feed on. These crops include: Chinese cabbage, tatsoi, mizuna, komatsuna, turnip, mustards, red Russian kale, and rutabaga. Other highly attractive brassicas include radish, daikon and arugula. These crops remain vulnerable to flea beetle damage at all stages of their growth.
Trap Cropping. Flea beetle preferences can be used against them, by planting a trap crop that is highly attractive near a less attractive crop. To be most effective, the trap crop should be planted completely around a field, rather than just in single rows. That way the trap crop can ‘intercept’ beetles wherever they try and enter the field. In order to keep the beetles from leaving the trap crop and moving to the adjacent main crop, they should be controlled with an insecticide soon after their arrival.
Chinese ‘Southern Giant’ mustard has worked well as a trap crop. It is best to make multiple sowings, several days apart, to provide an ample and continuous supply of attractive, young mustard plants that protect the main crop adequately. Do not let the mustard go to seed, or it could become a weed in future plantings.
Scouting. Whether you use a trap crop or not, newly planted fields should be scouted for flea beetles and flea beetle damage every day or two while plants are small and unable to tolerate much damage. Beetles can move into a field very quickly.
When scouting, it’s easier to count the beetles if the leaves are not disturbed. If there’s an average of 2 to 5 beetles per plant, some control is probably needed to prevent crop loss. The lower number applies to smaller seedlings. Larger plants can withstand more feeding injury.
Insecticides. For conventional growers, pesticides containing pyrethroids or carbamates (Sevin) are generally effective. On organic farms, rotenone was often used in the past, but it is not ideal because it is has a relatively high mammalian toxicity and its availability has become limited. Other materials often recommended for organic farms include neem or insecticidal soap but recent research indicates that these are not very effective. Other insecticides containing pyrethrins (Pyganic) or kaolin clay (Surround) have worked well in some studies but not others. Good control has consistently been obtained with the organic pesticide containing spinosad (Entrust) but this product is not yet labeled for flea beetle control. Insect repellents containing hot pepper or garlic may also provide some control. If you are an organic grower check with your certifying agent to be sure any material you use is approved for your use.
Commercial formulations of entomopathogenic nematodes may be helpful in reducing flea beetle damage. Applied to the soil, the nematodes attack beetle larvae, reducing root feeding and helping to prevent the next cycle of adults. For beneficial nematodes to be effective, they should be applied when larvae are present and the soil must not be allowed to dry out.
Row Covers. For non-chemical control, floating row covers can be very effective at preventing beetles from reaching the crop, if it is grown in rotation following a non-susceptible crop (otherwise, there’s a good chance that the pest will emerge under the row cover). Row covers must be put in place and sealed immediately after seeding or transplanting, before beetles have a chance to find the crop, which doesn’t take long.
Flea beetles are small and persistent, so row covers will only protect crops if there is no way for them to get in. The covers must be carefully sealed, ideally with a continuous layer of soil along the edge of the cover. If you use rock or sand-filled plastic bags to hold the edges down, be sure to place them close enough that they provide a tight seal, even when the wind is blowing. The older row cover gets the more tears it has, so avoid using worn row covers for flea beetle protection since tears allow entry.
When you remove the cover for weeding, replace it as soon as possible. If beetles do get under the covers, control them with insecticide, then re-cover. Don’t forget to go back and peek under the covers every few days.
Mention of insecticides and brand names is for information purposes only. No endorsement is intended nor is discrimination against products not listed. Always read and follow the label – it’s the law.