First shot fired by flea beetles in the battle of the garden

Bob Dluzen
Special to The Detroit News

Flea beetles are one of the earliest insect pests we see in the garden. We found them here a few days before the Memorial Day weekend munching away on radish leaves.

These small insects are called flea beetles because of their behavior of jumping away when startled. That jumping reaction looks very much like a flea jump.

This early brood of beetles are black in color and while not as small as a flea, they’re still pretty small at less than  1/16th of an inch long.

A cruciferous flea beetle on a radish leaf.

If you know what to look for, the symptoms of flea beetle damage are very distinctive and easy to recognize. Leaves on affected plants have a unique pattern left behind as the adults eat away parts of the leaves. The holes created by adult beetle feeding reminds you of the pattern that bb’s make in a paper target when they are shot out of a shotgun. Farmers call the leaf damage “shot-holes”.

The shot-holes are always separated and never merge together. On plants with thick leaves like cabbage, the tiny beetles are not able to chew all the way through and will often create pits or sunken areas instead of holes.

 It’s a good idea to carefully inspect your plants early and often. In many cases, if they’re not attentive, gardeners will not see the symptoms until quite a bit of damage has already been done.

Small seedlings are more susceptible to flea beetle damage than are larger plants grown from transplants. That’s because, given the same beetle population density, there is less leaf area on seedlings than on transplants.

Radishes are a favorite early spring food for the beetles so they give you a warning that more flea beetles will soon be attacking your plants.

There are more than one species of flea beetle and will vary a bit in size or color. They are also “species specific” feeders, meaning the ones that are eating radish leaves now are not the same species  that will be eating your eggplant leaves later on. However, in a practical sense in the garden, they can all be treated the same.

The first beetles in the spring seem to show up out of nowhere. But before your tasty radishes came up, the beetles were subsisting on broadleaf weed leaves. An alert gardener can sometimes spot the shot-holes in nearby weed leaves and be warned to be on the lookout. 

Nearly every vegetable plant can be attacked by flea beetles and heavy infestations will stunt plant growth and reduce yields.

On leafy salad greens, flea beetle shot-holes are very unappetizing.

 Floating row covers are an effective non-chemical way of preventing flea beetles. Those covers are made of extremely lightweight cloth that are placed over the crop to exclude insects while still allowing sunlight and rain to reach the plants.

You’ll sometimes see recipes online for homemade concoctions that are supposed to kill or repel flea beetles. One popular recipe is fresh garlic and water buzzed up in the blender. The resulting slurry is strained and sprayed onto plants to repel the insects.

Insecticides that are listed for use in home gardens, both conventional and organic, are very effective at killing flea beetles. Keep in mind however, that the beetles are so good at jumping away that they can often escape a spray application and will live another day to return to your crop.