Efficacy for powdery mildew on acorn squash of conventional and organic fungicide programs with biopesticides that induce systemic resistance, 2018

摘要

An experiment with field-grown squash was conducted at the Long Island Horticultural Research and Extension Center (LIHREC) in Riverhead, NY, in a field with Haven loam soil. The main objective of this experiment was to assess benefits of adding a biopesticide that triggers an induced systemic resistance (ISR) response in plants (Regalia or LifeGard) to a conventional fungicide rotation for powdery mildew on cucurbits. There was a parallel treatment with Serifel, another biopesticide, and a treatmentwith only organic-approved fungicides. The cultivar selected has intermediate resistance to powdery mildew. The field was plowed on 29 May.Weeds were managed between the mulched beds by applying Strategy 3 pt/A, Sandea 0.5 oz/A, and Roundup PowerMax 22 oz/A prior to seedling emergence on 29 Jun using a tractor mounted sprayer.The following fungicides were applied throughout the season to manage Phytophthora blight: Presidio 4 fl oz/A on 25 Jul, Ranman 2.75 fl oz/A on 30 Jul, Orondis Ultra 7 fl oz/A on 4 Aug, Revus 8 fl oz/A on 7 Aug, Omega 1.5 pt/A on 13 Aug, Orondis Ultra 7 fl oz/A on 23 Aug, Orondis Ultra 7 fl oz/A on 30 Aug, Omega 1.5 pt/A on 6 Sep, and Ranman 2.75 fl oz/A on 15 Sep. A randomized complete block design with four replications was used. Treatments were applied on a 7-day schedule using a tractor-mounted boom sprayer equipped with twinjet (TJ60-11004VS) nozzles spaced 17 in. apart that delivered 72 gal/A at 50 psi and 2.3 mph. Applications of Regalia, LifeGard, and Serifel were begun on 19 Jul, at least two weeks before plants were anticipated to begin producing fruit, which is when powdery mildew typically starts to develop. Plots were inspected for powdery mildew symptoms on upper and lower leaf surfaces on 24 Jul; 1, 7, 16, 24 and 31 Aug; and 17 Sep. For each assessment 5 old to middle age leaves and 5 young leaves were evaluated per plot.Colony counts were converted to severity values using the conversion factor of 30 colonies/leaf = 1% severity. Average severity for the entire canopy was calculated from the individual leaf assessments. Area Under Disease Progress Curve (AUDPC) values were calculated from 1 Aug through 17 Sep using the formula: Jji i=1[(Ri+1 + Ri)/2] [ti+1 - ti], where R = disease severity rating (% of leaf surface affected) at the ith observation, ti = time (days) since the previous rating at the ith observation, and n = total number of observations. Two measurements were taken per plot and averaged. Mature fruit were harvested on 19 and 20 Sep. All fruit was taken from each plot and counted (excluding rotten fruit caused by Phytophthora blight). Fruit was sorted based on marketability criteria: larger than 3.5 inches in diameter, fully ripe, andno large surface defects. Marketable fruit was weighed. Yield per healthy plant in each plot was calculated and used in analysis. Five representative fruit from each plot were analyzed for sugar content (Brix) using a refractometer. Data was analyzed with oneway ANOVA and Tukey's HSD to separate means using JMP statistical software. Average monthly high and low temperatures (oF) were 85/70 in Jul, 84/72 in Aug, and 77/66 in Sep. Rainfall (in.) was 3.76, 6.04, and 5.81 for these months, respectively. Dueto the atypically high amounts of rainfall in Aug, Sep, and Oct, Phytophthora blight was prevalent in the experiment despite efforts to control it. As the growing season progressed multiple plots were completely killed by Phytophthora blight and other plots were heavily impacted by the disease. As a result, one treatment had to be left out of statistical analysis because it did not have enough replications. Means from this treatment are presented from an observational context. Yield data was also heavily impacted by Phytophthora blight, rotten fruit was excluded from all yield measurements in an attempt to limit the impact of the disease on yield estimations.