Evaluation of Herbicide Damage to Grapes in a Unique Growing Season

The 2012 growing season presented a rare combination of extremes, a record mild winter followed by the earliest date for spring bud break on record.  Bud break of three to four weeks before normal averages recorded for numerous locations in Nebraska contributed to serious problems related to early bud break.  In a few parts of the state, a cold temperature event caused damage to shoots that had broken bud, but the most serious problem for many vineyard locations was damage to shoots from herbicide drift of volatile herbicides.  In most cases, this damage was attributed to 2,4-D.  This was the case for one of our research vineyard locations and led to our evaluating relative damage among a range of 5-year-old grape cultivars and genotypes.  Shoots were rated for foliar damage and stunting of shoots, and following a second herbicide drift occurence ratings for damage to flower clusters and fruit set were also recorded.  Significant differences were found for different cultivars and genotypes.  The most severe damage was sustained by 'Sabrevois', 'Marquette', and MN 1235.  The least injury was noted for 'Chambourcin', 'Seyval Blanc', 'Vidal Blanc', and MN 1258, with 'Frontenac', MN 1220, 'Valiant' and 'Saint Croix' intermediate in their symptoms.  In most cases, yield reductions were consistent with the damage ratings, i.e., the most yield depression was experienced by the genotypes that had the most severe damage ratings and the genotypes with the least damage rating produced a nearly full crop.