How to Rid Your Garden of Flea Beetles
Fleas in your garden? No, those are flea beetles, a variety of leaf beetle that jumps like fleas. The adults kill by spreading disease while the larvae kill by eating the roots of your plants.
Know your enemy
Flea beetles are tiny and shiny. They are about 1/10 inch long and black or tan metallic with either stripes or spots. They commonly feed on cruciferous plants such as cauliflower, cabbage and broccoli.
The adults overwinter in the soil, emerging when the temperatures reach 50°F. They are most harmful in the spring when they feed on your seedlings, killing them. Later in the season, when your plants are larger, the small holes they make in the leaves won't kill them. It's the diseases (wilt and blight) that they spread as they feed that can kill your plants.
As the adults feed, they mate and lay their eggs on the roots of your crops. When they hatch, the larvae feed on those roots for 2 to 3 weeks, destroying the plants. They then pupate in the soil for an additional 2 to 3 weeks, emerging as adults to start the cycle over again.
Fool me once
Fortunately, flea beetles are not terribly intelligent. You can fool them into thinking that there is nothing to eat by planting out your seedlings 2 to 3 weeks later than normal. The flea beetles will then move on in search of crops to which to feast and lay their eggs.
Alternatively, you can use floating row covers on your seedlings. They are "floating" because you just lay them loosely over your plants. The thin polyester material allows light and rain to get in but keeps insects out.
A variant of this strategy is to aggressively weed the area around your cruciferous plants. A 3 foot strip of bare soil will discourage the flea beetles who will go off to find something to eat that is easier to access.
Plant herbs such as thyme or mint that have strong scents among your crops to confuse flea beetles who will think that they have accidentally stumbled upon your herb garden. Or you can plant a trap crop such radishes that will lure them away. Root crops such as radishes can withstand the depredations of flea beetles because their roots for which you are growing them are not affected by adult beetles.
The enemy of my enemy is my friend
Plant flowers which bloom in umbrels such as fennel, dill or yarrow to attract beneficial insects such as tachnid flies and braconid wasps. The adults enjoy feeding on the pollen of the flowers while their larvae prefer to feast on flea beetles.
Make your own spray
Combine 5 parts water with 2 parts alcohol plus a tablespoon of dish detergent and spray the foliage of your susceptible crops. You will need to re-apply your spray after each rain event. This will only deter adult flea beetles. The larvae are underground feeding on the roots. Discouraging the adults from eating your crops will result in fewer larvae feeding on roots.
A deep cultivation of your garden in the fall will prevent adult flea beetles from overwintering in your soil so that you will have fewer of them to contend with in the spring.
More on garden pests
© 2014 Caren White