Phomopsis is a common disease of grapevines in all of the major grape producing regions of the world. It is the first of the major diseases to infect vines at the start of the season and is one of the "Big Five" diseases with which all vineyards in the Midwest and Eastern U.S. must contend (the others being black rot, powdery mildew, downy mildew, and bunch rot). Though it is commonly referred to as Phomopsis Cane and Leaf Blight it actually attacks all green tissues of the vine including the bunch stalk or "rachis" and the immature berries. While the level of susceptibility varies with the grapevine cultivar, all cultivars are susceptible to some degree. Many common cultivars grown in Missouri are moderately or highly susceptible to Phomopsis, including Concord, Catawba, Vignoles, Chambourcin, Chardonel, Seyval blanc, Vidal blanc, and Traminette.
The most common forms of Phomopsis infection are the cane and leaf blights. These infections take place shortly after growth commences in the spring and first appear 3 to 4 weeks later as small black lesions on the basal 2-3 internodes of the young shoot or as small chlorotic or pale green spots with dark centers on the basal leaves. The lesions on the shoots gradually enlarge and may coalesce into larger wounds that crack and give the basal area of the shoot a rough appearance. If enough lesions coalesce the shoot may be weakened and break under the stress of high winds. If heavily infected, the leaf infections can cause the basal leaves to pucker or become distorted, taking on a ragged appearance. The cane and leaf forms of Phomopsis infection do not cause serious economic damage in themselves, but since the basal internodes of the canes are the portion retained during winter pruning to become the fruiting units of the vine if they become infected the disease will overwinter on them and they will serve as the source of inoculum for the next spring. More importantly, new cane and leaf infections can also serve as sources of inoculum for berry and rachis infections in the current season.
Phomopsis overwinters in the vineyard on infected canes, including dead wood not removed from the vines during winter pruning, as well as any infected rachis left on the vine at harvest. So the first step in Phomopsis control is sanitation, i.e. the removal of any infected wood or tissues, including old, dead spurs. This is particularly important on old vines, where non-thorough pruning over the years may have left a lot of dead or infected canes or spurs, causing the buildup of a large amount of inoculum. There is some research evidence indicating that late dormant applications of liquid sulfur or lime sulfur may reduce the amount of overwintering inoculum, but not enough to prevent problems from developing. The most important step in Phomopsis control is the timely first application of a protectant fungicide. Phomopsis infections can take place when the shoots are only about 1¼ to 1½ inches in length, so the first fungicide application should be made when the new shoots are about 1 inch long. This timing is critical since the only fungicides that are highly effective against Phomopsis are the protectant materials mancozeb, captan, and ziram. We see Phomopsis lesions on basal internodes and leaves every year in many Missouri vineyards because the first fungicide application in those vineyards is not properly timed. And unlike black rot, powdery mildew or downy mildew for which there are materials that have a retroactive ability to stop young infections, there are no materials with retroactive or "rescue" ability against Phomopsis.
REVISED: December 1, 2011