Chesnut gall wasp: A threat to Michigan growers

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.   

The Michigan Department of Agriculture (MDA) recently announced the establishment of the Chestnut Gall Wasp Quarantine to protect Michigan’s chestnut industry from the devastating effects of a pest known as the chestnut gall wasp. This exotic insect has become established in nine states across the Southeast and Eastern United States. Chestnut gall wasp, Cynipidae: Dryocosmus kuriphilus Yasumatsu, is a tiny insect, which seriously damages all species of chestnut (Castanea), including the commercially-grown Asiatic and European species, as well as the once plentiful American chestnut. The gall wasp does not affect horse chestnut, which is not a true chestnut at all.

Female adult chestnut gall wasps lay eggs inside chestnut buds in early summer. After the eggs hatch, the larvae remain dormant until the following spring, making this pest difficult to detect during the initial year of infestation. During the following spring, the larvae induce gall formation on developing plant bud tissues. The galls suppress shoot elongation and reduce fruiting. Chestnut trees with severe infestations lose their vigor and often die.

MDA and Michigan chestnut growers met earlier in the year to discuss ways to prevent the introduction of this pest into Michigan, and thus assure the health of chestnut groves statewide. The exterior state quarantine, which was effective May 17, prohibits chestnut nursery stock coming from infested states unless strict regulatory requirements are met. The infested states include Alabama, Georgia, Kentucky Maryland, North Carolina, Ohio, Pennsylvania, Tennessee and Virginia. Growers that receive chestnut trees or scion wood from these states may not sell or further distribute the stock unless a written release is issued by MDA, similar to requirements used under the Hemlock Woolly Adelgid Quarantine.

Additional information about chestnut gall wasp quarantine is available on the Michigan Department of Agriculture web site at www.michigan.gov/mda.

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