Viticultural Information

Spotted cutworm, Amathes c-nigrum, larva feeding on bud.

The most common species attacking grapes are the variegated cutworm, Peridroma saucia (Hubner); the spotted cutworm, Amathes c-nigrum (L.); and the brassy cutworm, Orthodes rufula (Grote). These species can be found in both coastal and San Joaquin Valley grape-growing areas. Other cutworm species can occasionally cause damage. In vineyards these include the greasy or black cutworm, Agrotis ipsilon (Rothemburg), and the dark-sided cutworm, Euxoa messoria (Harris).

Cutworms have a broad host range that includes weeds and many types of useful plants including grapes. Damage to grapevines occurs from bud swell to when shoots are several inches long. Injured buds may fail to develop canes or clusters, which can cause significant yield reduction in some varieties. Temperature may lengthen or shorten the period of spring cutworm feeding. Grapevines can compensate for early season damage to buds or shoots by increased berry size and sugar. When primary buds are destroyed, secondary buds emerge. The fruitfulness of secondary buds varies according to variety. In certain varieties, such as Ruby Cabernet, secondary buds are as fruitful as primary buds, and the only damage that occurs if buds or short shoots are destroyed is delayed maturity. Other varieties, such as Thompson Seedless, are noted for having unfruitful secondary buds. Destruction of their primary buds can be expected to reduce the number of clusters in proportion to the number of buds destroyed. Less vigorous wine grape varieties also are expected to lose clusters in proportion to the number of buds destroyed.

When cultural practices, natural enemies, and climatic factors are not sufficient to hold cutworms to tolerable levels, insecticides may be used. Unfortunately, few modern chemicals are highly effective.