Effects of Organic Biofungicides versus Conventional Fungicides on Powdery Mildew in Pumpkins

There are challenges growing pumpkins (Cucurbita maxima)  in the southeast United States with weed, insect, and disease pressures. One of the major pests that infect pumpkins is powdery mildew (Phyllactina spp.), a fungal disease that can decrease photosynthesis and cause extensive early defoliation. Growers are advised to spray with fungicides every 7 days to achieve acceptable yields. With the increased interest in growing naturally/organically this study was initiated to trial the organic fungicides Oso (Polyoxin D zinc salt), Double Nickel (Bacillus amyloliquefaciens strain D747), and Cueva (Copper Octanoate) as compared to the inorganic standard Bravo WS (chlorothalanil) and Quadris (aoxystrobin). Three Pumpkin cultivars; ‘Early Giant’, ‘Mustang’, and ‘Gold Medal’  were direct seeded by hand 7 July at the North Mississippi Research & Extension Center in Verona Mississippi during the summer of 2014.  The treatments were initiated one week after emergence and applied as a foliar spray, at recommended label rates, on a 7 day interval using a motorized back pack sprayer until harvest. The experimental design was a randomized complete block with 4 replications. Plant beds were formed with a press-pan-type bed shaper, 6 in high and 30 in wide. In-row plant spacing was 2.0 ft and beds were spaced 12.0 ft apart, center-to-center. Every plot consisted of 18 plants, 3 from each cultivar, with each cultivar harvested separately. Plots were rated for percent disease on foliage every 14 days in August and September There were no significant disease foliage differences for the treatments.  However, among the cultivars Mustang had the best disease rating. The first harvest was 7 October, when the majority of the pumpkins were orange. Pumpkins were counted, weighed, and measured for height and circumference.  The treatments show that pumpkin weight, height, and circumference were reduced in the Double Nickel/Cueva mix. Also the standard treatment of Bravo WS/Quadris had the most number of pumpkins per plot, although not significantly different than Double Nickel/Cueva or the control.  The organic fungicides trialed demonstrated efficacy to be as effective as the conventional fungicides used in the current study.