Flea Beetle Infestation
Hello,. Every year we have a big problem with flea beetles. I have tried many things. Not composting infected debris in the fall, use of DE during growing season, use of nematodes, insecticidal soaps (homemade & store bought). I have now cleaned out the garden for end of season. Before or after fall tilling, whichever is best. What do you suggest I apply to the soil. We have a very large garden area. At this point I am not opposed to using non organic, but I would rather not. We also cover our garden ground with plastic during winter to cut back on the weeds. Thank you very much.
Columbia County Oregon flea beetles
Thanks for your question about flea beetle control. And congrats for (at least) trying to use organic methods to do that! As this Extension article explains, since these are highly mobile insects, 'doing something' to your soil--in any season--may have no effect on the beetle population. As you've undoubtedly read:
"Flea beetles overwinter as adults in leaf litter, hedgerows, windbreaks, and wooded areas. In early spring, the adults become active and, depending on the species, females will lay single or clusters of eggs in small holes in roots, soil, or leaves of many different plants. In home gardens, they are common on crucifers, including radishes, broccoli, cabbage, and turnips, eggplant, peppers, tomatoes, potatoes, spinach, and melons. Following egg hatch, small white larvae feed on the roots of the newly planted seedlings, usually causing little to no damage to the plants (with the exception of potato flea beetle larvae). Larvae then pupate in the ground. There are usually one to two generations per year."
So, although your garden may be 'squeaky clean' of infected debris, all it takes is for an area of like debris to accumulate in an neighbor's yard, and they'll find your plants in the spring! You said that you had tried nematodes, which, as this article indicates, has proven to be relatively effective. I wonder, though, whether you applied them at the correct time and used the ones which are specific to flea beetles (Steinernema carpocapsae and Heterorhabditis indica). It's not a 'one size fits all' solution. And they need to be applied when the insect is in its pupal stage (just before they become adult beetles.) This can be tricky to figure out!
But, if you've tried all of these, and need to resort to chemicals, this link has some available for home gardeners, to be applied to the plant foliage once the insect is in its adult stage. Just be sure to follow all label directions, and do not consume the plants before the end of the residual period.
Hope this is helpful. Good luck!