The 2012 ASHS Annual Conference

Captan is an effective protectant fungicide commonly used on a broad range of crops. When combined with surfactants and under conditions that enhance absorption Captan can cause severe phytotoxicity on grapes. A spray application error, resulting in an off-label application to a cultivar evaluation trial (part of the NE1020 Multi-state project), provided an opportunity to evaluate differences in sensitivity among cultivars to injury from Captan mixed with an emulsifiable concentrate (Danitol). Three- and four-year-old vines were sprayed with a tank mix of Captan (1 lb/A) and Danitol (16 fl. oz/A) on 4 August. Environmental conditions were favorable for uptake (warm, high humidity) before and at the time of this application. Injury to leaves, stems, and fruit was evaluated by three raters two weeks and three weeks after application. Damage ratings for all cultivars increased similarly across rating dates for all cultivars. Cultivars had significantly different injury ratings on leaves (P = 0.0124), stems (P < 0.0001), and fruit (P = 0.0002).  The most severely affected cultivars were hybrids (NY 81, and 'Chambourcin') while the least affected was a V. vinifera ('Carmenere'), but overall severity ratings overlapped substantially between hybrids and V. vinifera cultivars. All cultivars were severely affected and ultimately many vines died. Leaf chlorosis was apparent within one week of application. Leaf necrosis, longitudinal stem splitting and necrosis, adventitious root formation, fruit shriveling, and death all occurred later. The effect was lethal and systemic, affecting the trunk below the graft union and the root system. Captan should not be applied with or near in time to oils, emulsifiable concentrates, oil-based adjuvants, or any chemical that enhances uptake.