Project Number: 2072-22000-045-035-G
Project Type: Grant
Start Date: May 1, 2023
End Date: Oct 31, 2024
1. Evaluate the efficacy of biological fungicides for management of grape powdery mildew. 2. Develop a comparison table of biological fungicides registered on grapes in the PNW.
Tank mixes of biological fungicides and sulfur will be used for grape powdery mildew (GPM) management at the Botany and Plant Pathology Field Laboratory in Corvallis, Oregon. The treatments will be focused on evaluating whether tank mixes of several different biological fungicides and a low rate of Microthiol Disperss (MD) micronized sulfur would provide better control than using the low rate of MD alone. Treatments will be arranged in a randomized complete block design with each treatment replicated on four sets of at least five vines. Treatments will be applied using a hooded boom sprayer at 150 psi at a rate of 50 to 100 gal water/A depending on canopy growth. Fungicide treatments will be applied every 7 to 10 days starting at pre-bloom (BBCH 55) or when powdery mildew is first observed. Leaf and cluster data will be taken on the middle three vines of each experimental plot by randomly examining either 25 clusters or leaves on both the east and west side of the row for a total of 50 units examined per plot. The incidence and severity of powdery mildew will be recorded regularly during the season. Incidence and severity data will be analyzed by calculating the area under disease progress curve (AUDPC). This is calculated by multiplying the mean incidence from two observation dates by the number of days between observations where Yi is incidence of mildew at ith observation and Xi is the day of the ith observations) and adding together the values. AUDPCs will be calculated using the agricolae package and modeled with a generalized least squares linear model. Cluster severity percentages will be modeled using a generalized linear mixed model with block fitted as a random effect. Cluster severity treatment contrasts will conducted using the emmeans package and model fit checked with the DHARMa package. Information on the features and compatibility of various biological fungicides with sulfur and other common organic production materials will be collected from labels, company brochures, publically available efficacy trials and discussion with company representatives. Information will be simplified and placed in a table for easy comparison among products on topics such as tank mix compatibility. The table will be distributed at grower meetings and on the internet. Additional refinement of the table will incorporate grower testimonials and experiences with these products.