Efficacy of biopesticides for managing downy mildew in organically-produced cucumber, 2009.

摘要

The goals of this study were to evaluate biopesticides and fungicides approved for organic production using a cucumber cultivar that has exhibited relatively low susceptibility to downy mildew compared to other cultivars in cucumber evaluations conducted at North Carolina State University since 2005. This integrated approach was taken because downy mildew is considered a difficult disease to manage organically. K-Phite was the only biopesticide evaluated that is not approved for organic production. The biopesticides were compared to an organic standard treatment, the copper fungicide NuCop, and a conventional fungicide program of Manzate Pro-Stick during the vegetative period followed by Bravo during the harvest period. Only protectant fungicides were used for the conventional fungicide standard because the organic fungicides also lack targeted activity and mobility. Most biopesticides were tested alone. Organocide was tested at a low label rate tank-mixed with NuCop at a low label rate. Cucumber was seeded on 17 Jul and transplanted on 29 Jul into beds with black plastic mulch and drip irrigation in a field with Haven loam soil at the Long Island Horticultural Research and Extension Center in Riverhead. A late planting date was used to increase the likelihood of downy mildew developing during the experiment. Organic production practices were used. A blend of Pro-Gro 5-3-4 organic fertilizer at 1000 lb/A plus peanut meal at 625 lb/A was spread on 23 Jul over the rows to be planted and then incorporated by disking before laying plastic mulch. Neptune's Harvest hydrolyzed fish emulsion fertilizer (0.094 fl oz in 6 fl oz water) was poured into the transplant hole before planting. Weeds were controlled by hand weeding. Plots consisted of single 27-ft rows spaced 11 or 17 ft apart with 18 plants at 18-in spacing. The plots were 10 ft apart in the row. A randomized complete block design with four replications was used. Fungicides were applied weekly for 7 weeks beginning on 25 Aug, one day after symptoms were first observed, using a backpack CO2-pressurized sprayer equipped with an 8002E nozzle that delivered 74 gal/A at 50 psi. It was intended that the treatments be applied on a preventive schedule. Therefore, to obtain some initial suppression ofdowny mildew, a conventional fungicide with some curative activity but limited residual activity, Curzate 60DF (2.75 oz/A), was applied early on 26 Aug to the entire experiment. Downy mildew severity was assessed on 24 and 31 Aug; 8, 15, and 23 Sep; and8 Oct by estimating incidence of symptomatic leaves in each plot and rating severity on nine representative affected leaves. Incidence and average severity for symptomatic leaves were used to estimate canopy severity. Marketable fruit and culls were harvested on 5 and 13 Oct. Average monthly high and low temperatures (oF) were 83/68 in Aug, 74/58 in Sep, and 62/47 in Oct. Rainfall (in.) was 2.01, 2.39, and 5.78 for these months, respectively.