Effective Control of Powdery Mildew in Vineyards: Insights from UC Davis

Powdery mildew, caused by the fungus Erysiphe necator, is a persistent challenge in viticulture, affecting grape quality and yield. The W.D. Gubler Lab at the University of California, Davis, has conducted extensive research to identify effective fungicide treatments for controlling this disease. Here, we present key findings from their 2006 grape powdery mildew fungicide trial, providing valuable insights for vineyard managers and growers.

Grape Powdery Mildew Trial Overview

The trial was conducted at Herzog Ranch near Courtland, Sacramento County, California, focusing on the “Chardonnay” grape variety. The primary objective was to evaluate the efficacy of various fungicides in controlling powdery mildew. The experimental design involved field applications to 3-vine plots in a randomized complete block design with four replicates. Applications were made using high-pressure hand gun sprayers and backpack sprayers.

Key Findings and Results

The trial included a range of treatments, with notable results summarized below:

  1. Untreated Control:
    • Disease Severity: 98.5%
  2. KeyPlex 350 DP (10-14 days, 1 qt/acre):
    • Disease Severity: 95.5%
  3. KeyPlex 350 DP (10-14 days, 2 qt/acre):
    • Disease Severity: 93.3%
  4. Foliar Supreme (14 days, 5 pt/acre):
    • Disease Severity: 91.3%
  5. Sulfur Dust (14 days, 5 lbs/acre):
    • Disease Severity: 90.2%
  6. Quintec alt Rally (21-24 days, 5 fl oz/acre):
    • Disease Severity: 83.2%
  7. BioNatrol-M + Latron B-1956 (10 days, 1.7 l/acre):
    • Disease Severity: 81.2%
  8. JMS Stylet Oil (14 days, 3.3 l/acre):
    • Disease Severity: 75.0%
  9. BioNatrol-M + Latron B-1956 (2.2 l/acre):
    • Disease Severity: 73.8%
  10. BioNatrol-M + Latron B-1956 (14 days, 1.7 l/acre):
    • Disease Severity: 66.8%
  11. BioNatrol-M + Latron B-1956 (2.2 l/acre):
    • Disease Severity: 39.6%
  12. Elexa 4% + Silwet L-77 alt Flint (7-14 alt 14-21 days):
    • Disease Severity: 13.0%
  13. BAS 56000F alt Sovran (14 days):
    • Disease Severity: 11.5%
  14. Quintec alt Rally (14-21 days, 4 fl oz/acre):
    • Disease Severity: 10.4%
  15. Elexa 4% + Silwet L-77 alt Flint (7-14 alt 14-21 days):
    • Disease Severity: 7.6%
  16. BAS 56000F (14 days, 10.24 fl oz/acre):
    • Disease Severity: 6.7%
  17. Foliar Supreme alt Quintec (14 alt 17 days):
    • Disease Severity: 6.7%
  18. Elexa 4% + Silwet L-77 alt Quintec (7-14 alt 14-21 days):
    • Disease Severity: 5.3%
  19. Pristine + Latron B-1956 (14 days, 8.42 oz/acre):
    • Disease Severity: 3.3%
  20. V-10118 (14 days, 0.03 lb ai/acre):
    • Disease Severity: 2.3%
  21. Difenoconazole (14 days, 75 g/acre):
    • Disease Severity: 1.0%
  22. Difenoconazole (14 days, 50 g/acre):
    • Disease Severity: 0.8%
  23. BAS 56000F alt Pristine + Latron B-1956 (14 days):
    • Disease Severity: 0.8%
  24. Pristine (14 days, 12.5 oz/acre):
    • Disease Severity: 0.5%
  25. V-10118 (14 days, 0.02 ai/acre):
    • Disease Severity: 0.1%

Conclusion

This comprehensive trial demonstrates the varying effectiveness of different fungicide treatments in controlling powdery mildew in grapes. Notably, treatments involving combinations of Elexa 4%, Silwet L-77, Flint, Quintec, and BAS 56000F showed the highest efficacy, significantly reducing disease severity. Vineyard managers can leverage these findings to implement effective disease management strategies, ensuring healthier grape crops and improved yields.