In Washington State, aging vines and winter injury can be a recipe for grapevine trunk diseases. While eutypa cankers are the most common of trunk diseases, there are other causes of dead arm in vineyards, says a Washington State University pathologist.
Canker diseases are reported in both vinifera and labrusca cultivars of grapes, with eutypa (Eutypa lata) and Botryosphaeria spp. common causes of dead arm, said Dr. Gary Grove, WSU pathologist and AgWeatherNet director. Ten years ago, eutypa was the common cause of trunk cankers in Washington, he said. "But now, bot cankers (Botryosphaeria) are also involved with trunk diseases in the Pacific Northwest."
Two species of bot canker were recently found in British Columbia, Canada, vineyards, reports the Pacific Agri-Food Research Centre in Summerland. Several different species have been found in California.
Both cankers, caused by fungi, are generally seen in vines older than five or six years, Grove said.
Both diseases require predisposition, he said. "The vine needs to be predisposed to infection by some environmental factor or man-made factor, such as being hit by a tractor. In our area, the predisposition usually comes in the form of winter damage."
Symptoms of both diseases include delayed shoot emergence in the spring, tattering of leaves, and chlorosis early in the season, he said, adding that a wedge-shaped canker can be seen when the trunk is cut in a cross section. Yields are eventually reduced from the dead wood of the vine.
"You cannot distinguish these two diseases in the field by looking at the symptoms," Grove said. "The only way to distinguish between the two—and by and large it’s academic because they’re both managed in the same way—is through direct isolation on the growth medium or by PCR