Cabbage flea beetle

Summer is upon us and so is the gardening season. While the typical variety of brassicas (cauliflower, cabbage, radishes, etc.) may already be gone from the garden, there are a few possibilities for the adventurous home gardener. Some folks still may have a patch of arugula hanging on in this heat, or maybe you decided to let those radishes sit in the ground until fall. Perhaps there are some southern gardeners transplanted into southwest Kansas that just have to have collard greens growing throughout summer. Well, if that’s the case, you should definitely be on the lookout for one of the most common garden pests, the flea beetle. And not just any flea beetle, the cabbage flea beetle, Phyllotreta albionica.

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 Cabbage flea beetles infesting radish leaves.

Flea beetles can be differentiated by other tiny beetles inhabiting the garden by their large hind legs and habit of jumping around like fleas when disturbed. There are many flea beetle species that can be garden pests. The cabbage flea beetle can be differentiated from most other species by its food preference. Cabbage flea beetles love to feed on any brassica (cabbage, radishes, mustard greens, etc.). Furthermore, the cabbage flea beetle is shiny, metallic bronze while a similar brassica feeding flea beetle, Phyllotreta cruciferae, is shiny, metallic blue. The other species you may encounter in the garden feed on anything in the tomato family, including potatoes, eggplant and, of course, tomatoes.

Generally, flea beetles can become a problem in the spring on young plants. Adult beetles overwinter in soil among plants and emerge in the spring to lay eggs and feed on their preferred hosts; usually, healthy plants can outgrow flea beetle damage. Gardeners’ tendency to transplant larger starts aids in fighting off springtime feeding damage. However, as weather warms up, an unchecked population of flea beetles can easily grow out of control. This was the case for me a week ago during the 105 degree-plus weather. Despite the heat, I have (or should I say had) two different species of leafy brassica in my garden, arugula and Japanese mizuna. Both were tolerating the heat well with regular watering. I also have a small, 6 foot row of edible-pod radishes. These particular radishes do not form a tuber; rather they flower during the warm weather and produce edible, bean-like pods. I had detected flea beetles on these radishes multiple times, but the plants seemed to be growing fine and tolerating a bit of leaf damage. I had used some Neem Oil a few times to try to discourage their activity on the plants. After the hot weather and blowing wind was subsiding for the week I went out to inspect my garden and was awestruck at the amount of flea beetles present.

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Typical “shotgun” damage to leaves fed on by flea beetles.

In only a few days, the assumed benign presence of cabbage flea beetles had become an overwhelming infestation. The small patch of arugula was completely decimated, all of the mizuna as well. The radish plants, being larger, were not yet totally destroyed, but I imagine they would have been after one more day of feeding.

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A huge number of flea beetles could be seen infesting most of the plants’ large leaves.

There are several chemicals listed for control of flea beetles, in this case I used an application of carbaryl. But remember, if chemical control of flea beetles in the garden becomes necessary carefully read and follow all label directions and make sure that any flea beetle insecticides being used are registered for use on the crop and its growth stage.

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After spraying the garden, thousands of flea beetles were seen exiting the plants.

For the time being, the flea beetle activity has disappeared. However, flea beetle re-infestation can happen quickly. They are very mobile pests and there are multiple generations a year. I suspect my fight is not over. Aside from having preferred host plants present in my garden during peak flea beetle activity, one other factor may have contributed to my overwhelming infestation. This is a new garden spot; I simply broke up the sod and installed the garden. This particular area had abundant blue mustard (Chorispora tenella) growing as a weed during the spring. It is possible that this large area of blue mustard (a brassica!) was sustaining a healthy population of flea beetles and acting as an overwintering site. This information brings up a few great non-chemical control methods for controlling flea beetle (and other pest) populations. First, keep a sanitary garden; remove all host plant material at the end of the season to eliminate overwintering sites. This goes hand in hand with crop rotation as well. I certainly will not be planting those radishes, mizuna, or arugula in the same spot next year. Secondly, weed control in the garden can help prevent a lot of future headaches! Finally, planning proper planting and harvest times can help the plants avoid peak pest activity. But I want my collard greens and radishes!

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