How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Phomopsis cane and leafspot appears as tiny dark spots with yellowish margins on leaf blades and veins. Spots first show 3 to 4 weeks following rain. Leaf death may occur if large numbers of spots build up. Basal leaves with heavy infection become distorted and usually never develop to full size. On shoots, small spots with black centers similar to those found on leaves occur usually on a basal portion of the shoot. After spots lengthen a few millimeters, the epidermal layers of the shoots usually crack at the point of infection. Heavy infection usually results in a scabby appearance of the basal portions of the shoot. On clusters, spots similar to those that occur on shoots occur on the flower cluster stems.

Lesions on leaves, shoots, and clusters become inactive during the summer heat but rain just before harvest can cause light brown spots on clean berries and spots quickly enlarge and become dark brown. Berries may shrivel and become mummified. Infected canes appear bleached during the dormant season. Severely affected canes or spurs exhibit an irregular dark brown to black discoloration intermixed with whitish bleached areas. The black specks visible in the bleached areas are pycnidia that develop during the dormant season.

COMMENTS ON THE DISEASE

This disease is most severe in northern grape-growing regions (North Coast and northern San Joaquin Valley) where spring rains are common after budbreak; moisture is required for infection. Infections generally occur when shoots begin to grow. Spores are released in large quantities from the overwintering pycnidia on diseased canes and spurs. These are splashed by rain onto early developing shoots and infection occurs when free moisture remains on the unprotected green tissue for many hours.

MANAGEMENT

Spur and cane lesions provide most of the inoculum for new infections. Reducing the source of the disease is important. In table grapes, mark areas in the vineyard exhibiting poor budbreak in spring. Later examine these areas for disease symptoms. A treatment of liquid lime sulfur before rainfall in fall will reduce the viability of pycnidia as well as reduce overwintering Botrytis sclerotia and powdery mildew spores.

In all areas, spring foliar treatments are advisable if rainfall is predicted after budbreak. Apply materials before the first rain after budbreak and before 0.5 inch shoot length (and again when shoots are 5 to 6 inches in length). Contact materials such as copper, sulfur, ziram, mancozeb, and maneb must be reapplied after significant rainfall in order to protect shoots up to 18 inches in length. If several rains are predicted, use systemic fungicides (azoxystrobin and kresoxim-methyl).

PUBLICATION

UC IPM Pest Management Guidelines: Grape
UC ANR Publication 3448
Diseases
W. D. Gubler, Plant Pathology, UC Davis
R. J. Smith, UC Cooperative Extension, Sonoma County
L. G. Varela, UC IPM Program, Sonoma County
S. Vasquez, UC Cooperative Extension, Fresno County
J. J. Stapleton, UC IPM Program, Kearney Agricultural Research Center, Parlier
A. H. Purcell, Environmental Science, Policy and Management, UC Berkeley
Acknowledgment for contributions to Diseases:
G. M. Leavitt, UC Cooperative Extension, Madera County

Top of page