The 2011 ASHS Annual Conference

Spring frost events occur in the Midwest U.S. occasionally and can cause significant damage to grapevines. The extent of damage depends on the developmental stage of shoots at the time of the frost event. A very hard freeze usually kills all exposed green tissue, causing vines to develop shoots from secondary buds at count nodes, or latent buds from old wood. However, frost events that are at or near the critical temperature threshold can cause partial death of shoots resulting in development of lateral shoots from basal nodes. This leads to low vigor, non-fruitful shoots that become poor quality canes for the next season’s fruit production. After such a near critical temperature frost even in April 2010 we set up a trial to compare different methods of shoot manipulation on six grape varieties to determine the effects on current season’s crop and cane quality for the following season. On two varieties (Marquette and Sunbelt) shoots were either 1) tipped to remove the dead tissue (TIP), 2) cut back to the basal node (CUT), or 3) shoots and spurs completely removed back to old wood (RMVD). Control (CONT) vines were left untreated. On four varieties (Concord, Fredonia, Niagara and Catawba) only TIP, CUT, and CONT treatments were used. Fruit was harvested and yield, cluster number, cluster weight, and berry weight recorded. The following spring, canes were counted and graded by diameter as a measure of quality, with mid-diameter canes (8-12 cm) being most desirable. In 4 of 6 varieties tested, pruning treatments (TIP, CUT, RMVD) increased the number of high quality mid-diameter canes, and reduced the number of poor quality small diameter canes over CONT. This resulted in a much better situation for pruning the following season. Fruit yield was low and only Marquette and Catawba had enough fruit to harvest. On Marquette TIP resulted in highest yield and cluster number, while on Catawba, yield and cluster number was highest in CONT. We conclude from this study that growers should consider complete removal of frost-damaged shoots, if practical, to insure availability of high quality canes for the following season.