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.
- 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.
- Quadris Flowable (Group 11) at 6 to 15.5 fl oz/A. Use of an adjuvant is recommended. Do not apply more than 15.5 fl oz/A per cutting. Preharvest interval is 14 days for grazing or harvest for forage and hay. 4-hr reentry.