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Poster: Biology & Disease Mgmt: Chemical Control


Interruption and reduction of Erysiphe necator cleistothecia development utilizing fungicidal oil
L. THIESSEN (1), W. Mahaffee (2) (1) Oregon State University, U.S.A.; (2) USDA-ARS, U.S.A.

Ascospores are the primary inoculum source of Erysiphe necator in most regions that grapevine is grown and overwinter within cleistothecia that are formed prior to leaf drop. Preventative fungicides are concluded at véraison (BBCH 83), and E. necator has ample time to colonize large portions of the leaf tissue, mate, and produce cleistothecia. Interruption of E. necator sexual reproduction post-véraison using a fungicidal oil may reduce overwintering inoculum. Chardonnay vines were sprayed once with 1% Organic JMS Stylet Oil (Vero Beach, FL) in 2014 and 2015. Fungicide application treatments were made when cleistothecia primordia were observed on leaves (BBCH 89), then 7, 14 and 21 days after primordia were observed. Cleistothecia development was monitored by weekly sampling of 10 leaves, approximately 1.4 m from the ground, per plot beginning at harvest (BBCH 89). Cleistothecia were enumerated along a transect on the leaf, and treatments were assessed using pairwise comparisons. Stylet oil applications significantly reduced cleistothecia in both years (P < 0.05) with no effect of application timing in either year (P > 0.4). Despite a reduction in the number of cleistothecia produced, cleistothecia were present in all plots prior to leaf drop, indicating that there may be limited utility of a late season curative fungicide application for disease management.