Efficacy of Organic Fungicides for Control of Powdery Mildew, Downy Mildew, and Plectosporium in Pumpkins

Increased agritourism in the state of Virginia has led to an increase in the pumpkin planting acreage for pick-your-own operations across the commonwealth. Virginia pumpkin producers face yield losses from numerous sources, including several fungal diseases. The objective of this research was to compare the efficacy of certified organic fungicides against a conventional fungicide program for the control of powdery mildew, downy mildew, and plectosporium. Cultivar Warty Goblin pumpkins were grown in Rockville, Virginia during the 2016 crop season. Five different treatments (water, Kaligreen, Nordox, Regalia, and Bravo +Quintec/Proline) were assessed for their control of powdery mildew, downy mildew, and plectosporium. Disease observations and treatments were made weekly from August 12 – September 15. Disease ratings for powdery mildew showed that conventional fungicides provided the greatest control, with organic products Kaligreen and Nordox providing next-best control, statistically equivalent in some analyses. Regalia did not provide significantly better disease control than untreated water controls. Plectosporium disease severity was reduced the most in plots receiving conventional fungicides, with Nordox being almost as effective. Kaligreen provided no control of plectosporium. Regalia provided modest control, which in some analyses was significantly better than the untreated control. Downy mildew pressure was extremely limited, and no significant differences in disease incidence were seen among the treatments. In conclusion, several of the tested organic materials proved to be statistically as effective as the conventional fungicides in controlling both powdery mildew and plectosporium, although conventional fungicides provided numerically superior control for all diseases.