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Friday, July 17, 2015

Japanese beetle management options

Jeffrey Hahn, Extension Entomologist

Japanese beetles are being found in gardens and yards now. Although the first discovery of these pests was recorded on June, 18, it hasn’t been until more recently that they have become more abundant. Japanese beetles are challenging to deal with, especially when they are numerous. The following are non-chemical and chemical options for managing them.
Japanese beetles having their way with a grape leave.
Photo: Jeffrey Hahn, UMN Extension


A good non-chemical method is physical removal. To be effective, it should be done every day (or at least as regularly as possible). If you can only handpick these pests once a day, research shows the best time to do so is during early evening. Have a container of soapy water with you so that beetles that are brushed or picked off the plants end up in the water where they are killed.

For smaller plants, consider using a fabric barrier, like cheesecloth. The fabric is placed around the plants, preventing the Japanese beetles from getting at them. You can make your own or buy them from a garden store or online site that sells garden supplies (e.g. Gardens Alive). The fabric should be lightweight and allows light and rain in. Be sure to take the fabric off of any plants that are flowering so bees can reach them.

One non-chemical method to avoid is traps. Although they are popular and can capture an impressive number of beetles, what are found in the traps is actually just a small number compared to how many Japanese beetles are actually out there. Research from the University of Kentucky has shown that these traps actually attract more Japanese beetles than they capture; plants in these areas often suffer more damage than they would have without the traps.

If you are interested in using an insecticide, consider a low impact product like Neem. Neem does not actually kill them, but causes them to stop feeding. While this can be effective on small to medium numbers of beetles, it is less effective against large numbers. Another option is pyrethrins (containing piperonyl butoxide). Pyrethrins do not contain any residual; it is only effective on what it directly contacts and repeat applications are likely necessary.

If you would like to use a product with a longer residual, consider a pyrethroid, such as permethrin, bifenthrin, lambda cyhalothrin, or cyfluthrin. Another option is carbaryl (Sevin). Depending on the Japanese
Japanese beetles on basil.  Be sure to check to insecticide
the label to be sure the plants you wish to treat are listed.
Photo: Michelle Grabowski, UMN Extension
beetle numbers, you may need to make more than one application. Be careful not to apply one of these insecticides when bees are active.

Another option is the use of imidacloprid, a type of systemic insecticide (dinotefuran is a similar systemic insecticide but is less effective against Japanese beetles). It’s easy to apply and is long lasting so only one application during the summer is necessary. It does not kill Japanese beetles quickly but it does cause them to stop feeding, then they die a little later. It is important to note that this product is very toxic to bees. Avoid treating flowering plants (or plants that may still flower later this summer) that are attractive to bees.

When applying insecticides, be sure that the plant you wish to treat is listed on the insecticide label. This is especially important when treating fruits and vegetables. If the plant you wish to treat is not on the label, then do not make an application to it. Instead, find a product that is cleared for the plants you are trying to protect.

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