Per reports from Chestnut Hill Nursery in Florida, chestnuts can make growers a tidy little profit. They report wholesale prices for large, high-quality chestnuts range from $3 to $5/lb. (and higher for organically grown chestnuts). Retail prices can range from $3 to $10/lb.

However, just like any other crop, there are pests to contend with. One particular pest, the lesser chestnut weevil (LCW), is a serious one.

Researchers from Indiana University – C. Cheng Kao and George Hegeman (retired) – are seeking to identify a non-pesticide method to reduce LCW development and damage in harvested chestnuts without harming nut quality. They shared their work at the most recent Great Lakes Expo.

Their work is important because chestnut growers are optimistic about market expansion for the nut and are actively planting new orchards of blight-resistant trees (per reporting in 2023).

Culinary historian Michael Twitty wrote of chestnuts, “This was one of the most bountiful foods that America has ever known.” They can be roasted or used in savory dishes or desserts. Chestnuts can be processed into flour and used in baked treats or to make pasta.

And, interestingly, chestnuts, which are low in fat and high in vitamin C, are more similar to fruits than true nuts. They are versatile and profitable, so reining in LCW damage is crucial.

The LCW, about a quarter-inch long, is endemic to the eastern U.S. – but LCW infection of chestnuts has expanded westward with the planting of new orchards. In some areas, entire crops can become damaged and unmarketable.

Adult LCWs begin emerging from the ground in spring and summer, when they feed on chestnut pollen. After mating, the females lay eggs in chestnut kernels when the burrs start to dehisce (burst open). These eggs will develop into larvae that will feed on the kernels for 10 to 15 days, finally chewing their way out of the nuts to then enter the ground for further development.

The weevil larvae can do extensive damage to chestnut kernels. The damage, however, is not easily detectable until the nuts are prepared for human consumption.

Scouting for adults emerging from the soil is somewhat effective with a dark-colored pyramid trap. These traps should be set one per acre well before chestnut bloom occurs and checked twice a week, according to research from Michigan State.

The most effective way to identify weevil presence in an orchard is via limb-tapping over a light-colored sheet. LCWs will drop when a branch is jarred. A silver lining – adult weevils are considered poor dispersers, with an average flight distance of 700 feet.

Kao and Hegeman said LCW populations can be reduced by applying pesticides such as Carbaryl before burr dehiscing occurs. Carbaryl can harm a wide range of insects, however.

What else can a chestnut grower do? There are a few post-harvest treatments that have been used to handle the weevils: Soaking harvested chestnuts in water for 10 days or heating chestnuts to 120º F for 20 to 30 minutes can reduce or eliminate LCW emergence. But both methods can compromise chestnut quality.

Long soaking can cause the chestnuts to ferment; heat treatments can partially cook the chestnut kernels. Better treatments of harvested chestnuts are needed.

Kao and Hegeman looked to earlier work from Ferguson, McCullough et al. at Michigan State that suggested water curing for a shorter time could reduce LCW emergence (in their study “Post-harvest treatments to reduce lesser chestnut weevil larval emergence and damage in commercial chestnuts”). The Indiana University team is seeking to identify scalable processes that can inhibit LCW development without harming chestnut quality.

So they tested sequential water curing for five days, followed by carbon dioxide infiltration, with the goal of inhibiting LCW larvae development and maintain chestnut quality.

In 2023, 39% of the chestnuts harvested in a Bloomington, IN, orchard were infected. The IU researchers tested water curing them for five, six, 10 or 15 days before decanting the water and counting the number of larvae and examining the chestnuts for quality. They also looked for any fermented odors. (Note: Changing the water at days 2 and 4 will reduce scents of fermentation.)

It was discovered that water curing for just five days can inhibit LCW emergence without affecting kernel quality. However, water curing for up to 15 days will still not completely eliminate LCW development.

Previous testing proved using CO2 infiltration for 24 hours terminated all LCW development without harming kernel quality. So they combined that with the water curing.

The result? Water curing for five days and following that with CO2 infiltration can terminate LCW development and maintain nut quality as well. The combination a much shorter, more impactful post-harvest practice.

In addition, Kao and Hegeman noted that treated chestnuts can be stored in refrigeration – after water/CO2 treatment – for at least three weeks without a detectable loss of quality.

For chestnut growers looking to lessen the impact of the LCW and have more salable nuts, this information is priceless.