Eutypa dieback is a progressive disease of the woody tissues of the grapevine. It is mainly found in older vineyards. Symptoms may not show for several years after infection. Initial symptoms usually appear on one arm and are best observed in mid- to late spring when shoots are 10 to 12 inches (25 to 30 cm) long. Leaves are cupped, yellowish and smaller than normal. Shoots are stunted and have fewer and smaller fruit clusters.
Severely infected arms or vines develop fewer shoots each year and eventually die. Below the bark, a canker can usually be found surrounding an old pruning wound.
The fungus releases spores from the canker once the bark has weathered off. Most spores are released during late winter and early spring when temperatures are above 32ºF (0ºC) and more than 1/25 inch (1 mm) rainfall or snowmelt occurs. The fungus infects vines primarily through pruning wounds, which remain susceptible for a month or more.
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