Are you are seeing small “shotgun” holes in the leaves of your leafy greens, turnips, or radishes? If so, your garden is most likely infested with flea beetles.
What is a Flea Beetle?
Flea beetles are very small, shiny black beetles that jump when disturbed. They are less than 1/10″, and chew small round holes through leaves.
Flea beetles become active in their full adult stage in the warm days of mid-spring (usually in the beginning of June). They are attracted to plants by chemical cues, and begin to feed on the leaves of your crops. Younger seedlings are more susceptible to infestation than more established plants, which tend to outgrow flea beetle damage.
Crops Often Affected
- Asian Greens (Bok Choy, Tatsoi, Chinese Cabbage, Hon Tsai Tai)
- Mustard Greens
- Broccoli & Cauliflower when they’re seedlings
Activity Cycle of a Flea Beetle
- After a couple weeks of feeding, females lay their eggs in cracks in the soil.
- Larvae hatches and feeds on roots and root hair of plants.
- After a month in larval stage, larvae pupate emerge from the soil as adults.
- The second generation usually becomes active in mid-summer.
- A third generation may emerge later in the year. However, in Colorado the flea beetle typically subsides in July.
What To Do
Established plants can usually outgrow any minor damage caused by flea beetles. However, the infestation of seedlings tends to be more extreme and fatal. If flea beetles are eating your seedlings or young plants, it’s important to take action.
Easiest Option: If you find your garden infested, use an organic treatment once a week until the bugs are gone. We recommend diatomaceous earth, applied every week until the beetles subside. Diatomaceous earth is food grade and very safe. Or, use the organic spray Spinosad. These products can be found at most nurseries and garden centers, or purchased on Amazon.
Long-Term Option: Add floating row covers on your garden boxes. Row cover is a cloth made out of a light, permeable material, such as polypropylene or polyester held up over a garden by a frame or resting gently on the plants themselves. The standard brands are Reemay or Agribon. The light material allows air, water, and up to 85 percent of ambient light to pass through. The covers should be put on immediately after seeding or transplanting, before the beetles can find the crop. The Urban Farm Company offers sturdy frames for row cover to be attached to.
Advanced Gardening Option: Use radishes or mustard as a “catch crop”. A catch crop is sacrificed to lure flea beetles away from your other crops. Several times a day circulate a yellow sticky trap mounted on a yard stick around your garden and between plants to reduce flea beetle populations.