PEST

ALERT University of Missouri Extension Asian Chestnut Gall Wasp Dryocosumus kuriphilus Yasumatsu Chestnut species affected: • Chinese chestnut (C. mollissima) • Japanese chestnut (C. crenata) • European chestnut (C. sativa) • American chestnut (Castanea dentata) • Chinquapin (C. pumila) Photo: Gyorgy Csoka, Hungary Forest Research Institute, Bugwood.org Adult Asian chestnut gall wasp

Distribution and hosts Tree damage The gall wasp was introduced into This insect pest lays eggs in the buds North America in 1974 on imported chest- of chestnut shoots, and galls develop on nut cuttings. A native of China, the gall the shoot tips, leaves and catkins. These wasp is also considered a major pest in galls greatly reduce nut production and Japan and Korea. suppress shoot growth. After adult insects The gall wasp has been identified in emerge, the dried, blackened galls become Georgia, Alabama, North Carolina, Vir- woody and can persist on older limbs for ginia, Maryland, Pennsylvania, Maryland, several years. In cases of severe infesta- Kentucky, Tennessee and Ohio. Although tions, interior portions of the tree canopy the gall wasp has not been found in the die and trees are killed. Midwest, it is likely to be found in addi- tional areas as detection surveys continue. Biology D. kuriphilus may be established in an area Female adult wasps, one-eighth-inch for some time before it is identified. long, lay three to five eggs in a cluster The distribution of this pest in the Unit- inside chestnut buds in early summer. ed States is primarily due to the transport Multiple adults may oviposit in a bud, of infested seedlings to new areas and the with as many as 25 eggs per bud. Eggs exchange of infested scion wood used to hatch in 40 days and the larvae remain graft new trees. dormant until the following spring. As

PA100 Who to contact buds growth begins, larvae induce gall If you observe galls formation on developing plant tissues. on chestnut trees in a Larvae feed on the inner gall tissue for 20 previously non-infested to 30 days before pupating. Adult wasps site, please contact: emerge from the galls in late May and early June. Dispersal by wasp flight has Michele Warmund been at a rate of 23 km per year, however, MU Extension Horticulture Specialist dispersal of adult insects has been aug- 1-31 Agriculture Bldg. mented by prevailing winds. Division of Plant Sciences A new gall forms on a chestnut shoot tip during University of Missouri Prevention of further pest flowering. Columbia, MO 65211 dispersion 573-882-7511 Because the dormant larvae are not [email protected] easily detected on chestnut twigs, infested plant material, especially that used to propagate new trees, may escape detec- tion. Pruning and burning infested plant material may retard further movement of this pest. Chemical controls are not fea- sible on trees where nuts are harvested for human consumption. Currently, Univer- A gall develops on a leaf in July. sity of Missouri researchers are studying insect monitoring, trapping and disinfes- tation strategies. The purchase of seedling trees or scion wood from nurseries where the gall wasp has been identified should be avoided to limit the spread of this seri- ous pest.

Multiple galls develop on terminal shoots following gall wasp infestation.

A healthy, mature Chinese chestnut tree Older galls persist on chestnut shoots after adult at harvest. gall wasp emergence.

■ Issued in furtherance of the Cooperative Extension Work Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. Director, Cooperative Extension, University of Missouri, Columbia, MO 65211 ■ an equal opportunity/ADA institution ■ 573-882-7216 ■ extension.missouri.edu PA100 New 12/09; Revised 10/12/Web