by Courtney Llewellyn

The U.S. has nearly 1,000 farms producing chestnuts on more than 3,700 acres, per USDA-NASS data. The top producing states are Michigan, Florida, California, Oregon and Virginia. Demand for fresh and processed chestnuts is high and likely to increase, both nationally and internationally. However, as chestnut acreage increases and distribution of chestnut orchards expands, the availability of hosts for insect pests also increases.

Discussing potential ways of eliminating these emerging pests of commercial chestnuts through their research are Max Ferguson, Daniel Guyer, Louise Labbate and Deborah G. McCullough, all of the Department of Entomology at Michigan State University. They noted a native insect, the native lesser chestnut weevil, and an invasive insect, the Asian chestnut gall wasp (ACGW), have become growing concerns for Michigan producers. The research team is seeking to better understand the biology and impact of both pests to develop management options to mitigate damage in chestnut orchards.

The research team wanted to evaluate the efficacy of post-harvest heat treatment of potentially infested chestnuts and how the high temperatures would affect the crop. Their findings were presented at the 2021 Great Lakes Expo.

In 2020, the Michigan State team harvested nuts from four infested orchards on four separate harvest dates. These chestnuts were submerged in 120º F water for 20 minutes, 30 minutes or left untreated. The treated nuts were held for five weeks to monitor any larvae emergence. A subset of these nuts were dissected immediately after treatment to assess their quality. Additional subsets of treated and control nuts were returned to cold storage and dissected at four-week intervals to monitor treatment effects on nut quality.

The good news: On average, larval emergence was reduced by about 85% in chestnuts submerged for 20 minutes. This treatment delayed emergence by 11 days compared with the untreated nuts. Nuts submerged for 30 minutes had no larvae emerge. The bad news: Internal quality was affected in the 30-minute group.

What’s next? The researchers are conducting post-harvest heat treatments to assess the efficacy of submerging chestnuts in water heated at 110º to 140º for five to 30 minutes (at five-minute intervals). A thermoprobe inserted into the nuts will monitor their internal temperatures. The treated and control nuts will again be held for five weeks to assess larval emergence and the treatment effects on nut quality.