By Chuck Ingels, Paul Verdegaal, Doug Gubler, and Ria DeBiase: UCANR

For many years, Eutypa dieback, caused by the fungus Eutypa lata was thought to be the main dieback disease of grapevines, causing death of spurs and cordons.

The disease resulted in a gradual but severe decline in yields. Although Eutypa is still present, its effects are complicated by other aggressive pathogens, mainly species in the Botryosphaeriaceae family, some of which are able to colonize wood tissue three times faster than E. lata. Nine Botryosphaeria species have been isolated from grapevine cankers from California. The disease they cause is referred to as “bot canker”.

Symptoms

Like Eutypa dieback, typical symptoms caused by bot canker on grapevines in California are the wedge-shaped canker in cross-cut cordons and dead spur positions. Eutypa dieback causes stunted shoots and leaves that are chlorotic, tattered, and cupped, but bot canker produces no foliar symptoms – i.e., the spur dies before spring push. Both diseases can be found on vines about seven to eight years of age and older or are common in vineyards older than 10 years. In susceptible varieties infection may occur after only four to five years when large cuts may be made during pruning.

Spore release

Eutypa lata overwinters in diseased wood and produces fruiting bodies called perithecia under conditions of high moisture (areas with rainfall exceeding 16 inches). Sexual spores (ascopores) are discharged from perithecia soon after rainfall. Infection occurs through pruning wounds, which remain susceptible much longer in December than in February.

Pruning wounds can be susceptible to infection by E. lata for seven weeks or more in late fall, but this varies with the time of pruning, size of the wound, and age of the wood pruned. With Botryosphaeria, asexual spores (conidia) are produced from black fruiting bodies called pycnidia during the entire season, including and perhaps especially in spring when temperatures are more conducive for sporulation. Another important source of pycnidia may be the shredded prunings or portions of arms and spurs left in the vineyards.

Varietal susceptibility

Wine grape varieties differ in their susceptibility to these diseases. In a 2003-2004 California survey, Botryosphaeria was isolated most often from Sauvignon Blanc (64 percent recovery from cankers tested) followed by Chardonnay (55 percent). Cabernet Sauvignon had the most cankers with Eutypa (58 percent).

Petite Sirah is extremely sensitive to infections as is Chenin Blanc, while Zinfandel and Syrah are moderately susceptible.