P-104 - Repeated fungicide application improves wound protection in early pruned grapevines from Botryosphaeria dieback

Botryosphaeria dieback is one of the dominant Grapevine Trunk Diseases (GTDs) causing cankers globally and in Oregon vineyards. Delayed pruning and use of wound protectants soon after pruning are effective strategies to manage GTDs. However, late pruning is often challenged by labor shortages, and rain during typical pruning time in Oregon. A study was done to assess the need of repeated application of fungicides when vines were pruned in December, January, or February. Freshly pruned vines were treated with thiophanate-methyl and sealant. December pruned vines received either three, two or one-time application, January pruned vines received either two or one, and February pruned vines received one application of each fungicide. Dothiorella iberica (2.5 x 10^4 spores/ml) was spray-inoculated on treated wounds. Wound tissues collected at the end of August were cultured in half strength PDA amended with antibiotics for pathogen isolation. Percent recovery of D. iberica was calculated and subjected to analysis of variance. In all months, one time application of thiophanate-methyl reduced pathogen recovery as much as repeated applications with average recovery ranging from 0 to 18.8%. Three times (12%) and two times (19.3%) application of sealant significantly reduced pathogen recovery compared to one time application (29.7%) and non-treated control (57.3%) in December. Results suggest that single application of thiophanate-methyl is sufficient to reduce D. iberica infections while repeated application of sealant can further reduce infections compared to single application.