PHOMOPSIS CANE AND LEAF SPOT AND FRUIT ROT
Description
Symptoms
Disease Cycle
Control

Description:
Phomopsis is a fungal disease of canes, leaves and fruit and was previously referred to as "dead arm". However, "dead arm" is now known to be two different diseases, Phomopsis canker and Eutypa dieback, which often occur together. Eutypa dieback is characterized by cankers and dieback of the cordons while Phomopsis lesions and cankers on stems are shallow and do not result in dieback of the cordons. Bunch grape varieties vary in their susceptibility to phomopsis fruit rot (Table 1). The disease is not common on muscadine grapes.

Symptoms:
Phomopsis infections can occur on all green tissues. Distinct black elliptical lesions on shoots (Fig.1) are the most common symptoms observed. . If shoot lesions become numerous, they coalesce and appear blackened and scabby (Fig.2). Cracks may form in large lesions during periods of rapid shoot growth. Lesions on leaves are usually circular, while those on the petioles are elongated. Both appear brown or black and are often surrounded by a small yellow halo. Rachis infections are common and are characterized by necrotic circular to elongated lesions. Fruit rot does not occur in many grape growing areas, but in warmer regions of the Southeast, the pathogen may infect fruit, causing it to turn brown and become covered with black, pimple-like fruiting bodies (Fig.3). These fruit eventually shrivel into mummies that are often confused with black rot mummies.

Disease Cycle:
Phomopsis viticola, cause of phomopsis cane and leaf spot and fruit rot, overwinters as black fruiting bodies (pycnidia) on canes, wood, and fruit infected the previous season. In springtime, when weather is cool and wet, tiny spores (conidia) are released from pycnidia and are splashed by rain to young shoots and leaves. Distinct black lesions form on shoots and leaves, and if wet weather continues, serve as an additional source of inoculum for infections of rachises and young fruit. These infections may occur from just prior to bloom until fruit is pea-sized, at which time the fungus becomes latent due to the warmer summer temperatures. At harvest when grapes mature, the latent infections become active in ripening fruit, which eventually rot, turn brown and shrivel into mummies. Fruit infections can also arise from lesions on the rachis or pedicels, which expand into the ripening fruit. Pycnidia are produced over the surface of the rotting fruit.

Control:
Cultural - Good horticultural practices that affect canopy microclimate in conjunction with sanitation are key to successful management of phomopsis disease. Dead wood, rachises, diseased canes and mummified fruit on the vine and ground are all overwintering sites for P. viticola. Thus, it is essential to prune and carefully clean up during the dormant season to reduce the inoculum carried over to the next season.

Chemical - Refer to the Winegrape Spray Program in the North Carolina Agricultural Chemicals Manual for current recommendations for phomopsis control

(http://ipm.ncsu.edu/agchem/chptr7/706.pdf). Successful management of this disease is dependent upon application of fungicides during early-season infection periods. The prebloom through postbloom sprays are most critical for preventing fruit infections. In problem vineyards, fungicides may need to be started at 1-inch shoot growth.