What are the best organic methods for dealing with a blister beetle infestation?
Answer: For many market farmers, blister beetles can wreak havoc on crops in a very short time. The beetles seem to prefer tomatoes, potatoes, and chard, but easily move on to peppers and eggplants. More importantly, they infest hay and are poisonous to animals feeding on the hay, even if the beetles are no longer alive, due to the presence of a toxic chemical in their bodies called cantharidin. Handling the adults should be avoided, as cantharidin can irritate or blister skin on contact. If handled gently, this may not be a problem.Populations tend to appear suddenly in June and July and usually will feed together in groups. Blister beetles usually overwinter as last-stage larvae and prey on either grasshopper eggs or bee eggs, so keeping grasshopper populations low is necessary to effectively reduce blister beetle populations. If grasshopper populations are high one year, there is increased likelihood that the following year will see higher than normal blister beetle populations.Some effective options to control the adults are pyrethrum, a broad-spectrum botanical insecticide, and a kaolin clay product sold under the brand-name Surround. Surround is not directly toxic to the beetles but acts in two ways: it changes the color of the plant, thereby confusing the insect, and it also causes most insects that land on a kaolin clay-coated plant to spend much time grooming themselves to remove the clay particles. This reduces the time they spend feeding. Keep in mind that many plants can withstand considerable defoliation before there is a decrease in yield. Neem-based products (containing Azadirachtin) have also reportedly been effective against blister beetles, though if you have a large infestation of blister beetles, you might consider using a formulation of spinosad. Other management strategies include early planting and harvest of crops to avoid the June/July peak blister beetle season. Row covers are also an option, but you must be sure that no beetles will emerge beneath (inside) the row covers. If your plot is relatively small, then the beetles, which tend to congregate in one area, can be knocked into a bucket of soapy water, which will kill them. Using a preferred crop or even a preferred wild host like passion vine as a trap crop is also an option; the trap crop can then be treated for the beetles. Lastly, creating environments attractive to blister beetle predators, including robber flies and birds such as meadowlark, bluebird, and scissor-tailed flycatcher, can help reduce the population.See ATTRA’s ecological pest management database and sourcing information for the above-mentioned biorationals.For more information, see the following ATTRA publications:Biointensive Integrated Pest ManagementFarmscaping to Enhance Biological ControlGrasshopper ManagementThe mention of specific brand names does not constitute an endorsement by ATTRA, NCAT, or USDA.