Cause Several fungi with the most important in Oregon being Phoma sp., Pseudopeziza trifolii (common leaf spot) and Polythrincium trifolii (sooty blotch). Other fungi causing leaf spots in Oregon include Ramularia sp., Stemphylium sp., and Stagonospora meliloti. Colletotrichum sp. (anthracnose) have been reported to cause leaf spot in Washington. Most of the fungi listed above survive in infected plant stubble and residue. Leaf spots are more severe on the early crop and tend to disappear on the second cutting during the summer. Leaf spots, though conspicuous, seldom cause serious losses.
Symptoms Light brown to black spots on the leaves.
Cultural control
- Plant recommended varieties.
- Cut early to reduce leaf loss and fungal inoculum.
Chemical control Foliar fungicides effectively reduce disease severity and may be considered for clover seed crops.
- 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.
- Regalia (Group P5) is registered for use on clover for other pathogens and can be used for common leaf spot on clover in Oregon. Apply at 1 to 4 quart/A on 7- to 10-day intervals starting prior to infection. Under high-disease pressure, use in combination with another fungicide. Does not benefit from the addition of an adjuvant. 4-hr reentry. O