Interruption and reduction of Erysiphe necator cleistothecia development utilizing fungicidal oil

Authors: THIESSEN, LINDSEY - North Carolina State University; Neill, Tara; Mahaffee, Walter - Walt

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2018
Publication Date: 5/1/2018
Citation: Thiessen, L., Neill, T.M., Mahaffee, W.F. 2018. Interruption and reduction of Erysiphe necator cleistothecia development utilizing fungicidal oil. Plant Health Progress. 19:153-155. https://doi.org/10.1094/php-11-17-0070-rs.
DOI: https://doi.org/10.1094/php-11-17-0070-rs

Interpretive Summary: The research test whether disruption of overwintering inoculum using timely horticulture oil applications is effective in disease management of grape powdery mildew. While there was significant reduction in overwintering inoculum development, it is not sufficient to reduce the potential for overwintering. Thus, it is not likely economical to utilize post-veraison oil applications to reduce the potential of inoculum overwintering.

Technical Abstract: Grape powdery mildew epidemics, caused by Erysiphe necator, are initiated by the release and subsequent germination of ascospores from mature cleistothecia. Interrupting the development of cleistothecia prior to overwintering may reduce or prevent the overwintering of E. necator in vineyards thereby reducing initial disease incidence observed the following growing season. At the end of the grape growing season in 2014 and 2015, one application of Organic JMS Stylet Oil (Vero Beach, FL) at a rate of 10 ml/L was applied at 4 treatment dates using an air-assisted backpack sprayer onto Chardonnay grapevines within a vineyard. Leaves were collected weekly and cleistothecia enumerated from the first observation of cleistothecia primordia development until the onset of rains (approximately 5 weeks). In 2014, all stylet oil treatment plots developed significantly fewer cleistothecia than non-treated control plots in 2014 (P = 0.04) and there were no differences in treatment date observed. No treatment differences were observed in 2015. Since cleistothecia were still produced despite stylet oil treatment, a single post véraison stylet oil application to interrupt cleistothecia development would not be an economical management option for reduction of grape powdery mildew.