ARS | Publication request: Evaluation of Actigard and Fungicides for Managing Phytophthora Fruit Rot of Watermelon, 2010

Submitted to: Plant Disease Management Reports
Publication Type: Research Notes
Publication Acceptance Date: January 30, 2011
Publication Date: March 28, 2011
Citation: Kousik, C.S., Thies, J.A., Harrison Jr, H.F. 2011. Evaluation of Actigard and Fungicides for Managing Phytophthora Fruit Rot of Watermelon, 2010. Plant Disease Management Reports. 5:V058.

Technical Abstract: Phytophthora fruit rot caused by Phytophthora capsici is an emerging disease in most watermelon producing regions of Southeast U.S., and has been considered as a top research priority by the National Watermelon Association (NWA). Managing Phytophthora fruit rot can be difficult because of the long duration of contact between the soil and the fruit, and the difficulty in getting fungicides through the plant canopy to the fruit. We evaluated several old and new fungicides for managing Phytophthora fruit rot at the US Vegetable Laboratory farm in Charleston, SC, in 2010. The seedless mini-watermelon cultivar Vanessa was used in these experiments and plots were sprayed weekly for a total of five applications with various fungicides. Plots were inoculated with a mixture of mefenoxam sensitive and insensitive isolates after the first three sprays. Fruit rot data was recorded in the field two weeks after inoculation. Symptomless fruit harvested from the plots were then inoculated by placing a 7-mm agar plug from a 3-day old actively growing isolate of P. capsici and placed in a room maintained at high relative humidity (RH>95%). Five days after inoculation the lesion diameter and sporulation intensity on each fruit was measured. Significant fruit rot was observed in the field on non-treated control plots to consider the trial effective. Highly significant differences were observed among the fungicide treatments. The rotation of Presidio and Revus was the best treatment in the field in 2010. Application of Actigard every week also significantly reduced fruit rot. Forum, Zampro, Prophyt + Kocide and Revus rotated with Prophyt + Kocide treatments significantly reduced fruit rot compared to non-treated control in the field. Ridomil Gold treatment was not significantly different from the control. In further studies conducted with harvested fruit, Zampro, Forum and rotation of Presidio with Revus offered extended protection to the fruit compared to the non-treated check. However, the treatments containing Actigard or Prophyt + Kocide were not significantly different from the non-treated check in the humid chamber. Further studies to confirm the effectiveness of these fungicides will be conducted in 2011.