Itch Mite Problems

— Written By Michael Waldvogel
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Fall is the time of year when hay/straw bales are used extensively for decorations at fairs and retail stores, hay rides and for covering areas that have been seeded to establish lawns for next year. It’s also the time of year we get calls and emails from people breaking out in rashes after handling or sitting on these bales.

The culprit is the “straw itch mite”, Pyemotes tritici, which commonly breeds in stored grain, dried beans and peas, wheat straw, as well as hay and other dried grasses used as animal feed. The mites are actually beneficial because they attack insects that feed on stored grain and similar materials. Anyone handling mite-infested materials will be attacked. The bites of straw itch mites are characteristically found on the trunk of the body and on the arms (where they’ve been holding the bales as they carry them).

Unfortunately, control options are limited. One of the best control strategy is to eliminate the mite’s host insects in the infested material. While it’s probably too late at this point, cleaning storage areas thoroughly and treating them with a pesticide, such as cyfluthrin, can help but is not likely to stop the problem entirely. The problem is complicated because there aren’t many chemical options for treating the bales. People have tried spraying soapy water (similar to the way we use insecticidal soap) or a horticultural oil but technically, these are off-label applications. Even if there were chemicals appropriately labeled, treating the straw is difficult because the mites are not just on the surface; they are deep inside the bales as well. So, surface treatments will not rid the bales of either prey or predators. Landscapers using potentially infested bales can apply repellent to their shirts, pants and arms to provide some relief from the mites’ attack. They can also treat the straw and after spreading it; although the value of such treatments are marginal since the major problem occurs when  handling the bales before they’re used.

If necessary, stored commodities can be fumigated with a product such as Phostoxin®. Fumigation should be performed by individuals holding a North Carolina F-phase structural pest control license or certification. Fumigation has many potential pitfalls on which I will not elaborate here since it’s unlikely that most people handling hay and straw would use it.

There really isn’t much we can offer in advice for people who may sit on infested bales at exhibits or hay rides. If users find that bales are infested, placing a plastic tarp over the bales before anyone sits on them may help somewhat.

– Mike Waldvogel