Phomopsis is commonly known as an early-season foliar and shoot disease that favors prolonged wet periods and cool temperatures. It also infects canes and was considered a part of the “dead arm” complex in the past. Lower internodes of shoots and basal leaves develop symptoms first. Leaves develop small (< 1/8 inches) yellow spots, which may become dark specks with yellow halos, and then the center of the lesion may eventually fall out to create a shot hole symptom. Dark sunken necrotic lesions on the shoots start as spots, but as the season progresses, they can elongate, sometimes coalesce, and become scabby.

Infection can happen on the rachis to cause premature berry drop and on berries to cause rot. Phomopsis symptoms on canes become visible during the dormant season. Often, infected canes look bleached in color, and fungal fruiting structures, which are the size of a ground black pepper and dark in color, may be observed in winter and spring.

(Photo Credit: Mizuho Nita)

Causal agent – Phomopsis viticola is the fungal species responsible Phomopsis cane and leaf spot on grapes. P. viticola can reside on previously infected canes and cordons to cause infection in the spring.

Management – Phomopsis spores are released in spring following bud breaking during prolonged wet periods with cool temperatures. Infection occurs 3-4 weeks before symptoms appear, therefore early season fungicide programs are essential for control of the disease. The application of mancozeb or captan products, starting when shoots are 1-2 inches in length, is often recommended. 
Fungicide applications should be considered when precipitation is expected after bud break. Depending on the frequency of rain events, a strict spray schedule (7- 10 days interval) may be applied until shoots reach approximately 6 nodes. After this period, many fungicides recommended for black rot and/or downy mildew can also be used to protect tissues from Phomopsis infection.
Cultural management practices involve reducing the amount of inoculum in the vineyard by removing symptomatic canes, dead spurs, and cordons. Canopy management practices that promote good air flow and reduce leaf wetness periods of vines are also important to reduce the risk of infection on green tissues in the spring.

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