Black rot control and bud cold hardiness of "Noiret" winegrape

Abstract: Black rot, caused by Guignardia bidwellii (Ellis) Viala and Ravaz, and bud cold hardiness are both management issues in eastern U.S. viticulture. Black rot infections lead to vine stress, resulting in premature defoliation and rotten fruit, potentially compromising cold acclimation of the vine. No studies have targeted bud cold hardiness in relation to severity of prior season black rot infection. Thus, in 2011, �Noiret�, a hybrid winegrape, was subjected to four black rot control treatments: conventional (C), organic 1 (O1), organic 2 (O2), and no spray (N). Leaves and fruit were scored for black rot severity. The O1 and N treatments had the highest level of leaf and fruit disease severity and were not significantly different. The C treatment had the least amount of leaf and fruit disease severity and the O2 treatment was intermediate and significantly different from the O1, N, and C treatments. Bud samples were taken in January, February, and March 2012 and exposed to subzero temperatures (-21 �C, -23 �C, -26 �C, -29 �C) in an ethylene glycolbath to assess if prior season black rot infection impacted primary bud hardiness. In January and March nearly all buds were still alive at -21�C and -23�C, but -29�C caused more damage. Black rot control treatments were not a statistically significant factor in the bud hardiness experiment. This could be due to black rot severity being below a critical threshold for impact or the vines had enough time to recover in late summer and fall to reach full mid-winter hardiness.