The American Chestnut was once the dominant tree species in much of the eastern United States. Breeding efforts following the devastating chestnut blight in the early 1900s have made growing chestnuts an increasingly viable option for producers. Pest pressures still limit production, however. Lesser Chestnut Weevil (Curculio sayi) larvae feed inside of chestnuts rendering them unmarketable and causing substantial losses. This project evaluates the viability of two biological control agents, entomopathogenic nematodes and entomopathogenic fungi, for the control of Chestnut Weevil. The entomopathogens have proved effective in controlling other, related, weevils. We seek to establish their effectiveness as an attractive, environmentally friendly, control option for organic chestnut production. Success in this project would remove a primary barrier to productive chestnut production and facilitate economic development in this nascent industry.

Since the introduction of Chestnut blight more than 100 years ago, American Chestnuts virtually perished from United States forests. Demand for chestnuts remains high, however. Annually, the United States imports more than 3000 metric tons of chestnuts to support latent demand. Despite now being able to help chestnut production with the development of blight-resistant varieties, the United States lacks a vibrant chestnut industry. This absence is due in part to a lack of effective control options for chestnut pests. Chestnut Weevils feed on the nuts and can cause losses exceeding 90%.

Male and Female Chesnut Weevils

A male (upper) and female (lower) Chestnut Weevil

This project seeks to demonstrate that biological control using entomopathogenic fungi and entomopathogenic nematodes is a viable method for control of Chestnut Weevil in the Northeast. Success in this project will provide producers with an environmentally friendly, practical way of increasing organic and conventional chestnut production.

To evaluate the effectiveness of biological control of Chestnut Weevil (Curculio sayi) two field trials are in use: production plots and microcosms. Production plot trials assess the potential for biological control of Chestnut Weevil in production chestnut systems. The experimental plots established at Rose Valley Farm in Rose, NY, are in a mature chestnut grove with Chinese, American, and European Chestnut varieties. This farm has a history of Chestnut Weevil infestation and a track record of producing high quality, organic chestnuts.

We evaluated field soil samples before any treatment applications. No entomopathogenic nematodes were detected, but entomopathogenic fungi(EPF) were: Metarhizium and Beauveria. Chestnut Weevil populations at Rose Valley Farms peaked in late October during 2019. The pyramid trap design we used captured significantly more Chestnut Weevils than the trunk or cone trap designs. EPF treatment seemed to have consistently lower Chestnut Weevil compared to controls.

Pyramid Trap

A pyramid trap nestled next to a chestnut tree at
Rose Valley Farms in Clyde, NY

More research will help us to understand the biology of Chestnut Weevils. Knowing more about these organisms and how they are affected by and affect their environment can aid us in better utilizing biological control techniques.