Cause A fungus, Erysiphe trifoliorum (formerly E. polygoni), which overwinters on the plant and on diseased crop residue. It seldom seriously reduces seed production, but it can reduce forage yield and quality. The disease is common on red clover and occasionally on white and alsike clovers.
Symptoms Leaf surfaces are covered with pale gray, powdery fungus growth. Severely infected leaves yellow and die.
Cultural control Plant recommended varieties.
Chemical control
- Azoxystrobin formulations (Group 11) including Azoxyzone, A-Zox 25SC, Quadris Flowable, Satori, Tetraban, and Trevo at 6 to 15.5 fl oz/A or Azteroid FC 3.3 at 3.9 to 9.7 fl oz/A. Do not apply more than two sequential applications of Group 11 fungicides before alternating with a fungicide that is not in Group 11. 4-hr reentry.
- Badge SC (Group M1) at 0.5 to 1.8 pints/A on 7- to 14-day intervals. Preharvest interval is 0 days. 48-hr reentry.
- Sulfur formulations including Super Six Liquid Sulfur, Sulfur 6L, Sulfur 80 WDG, Sulfur 90W, and Suffa Flowable Elemental Sulfur. May be applied up to the day of harvest. 24-hr reentry.