- Perhaps the most common clover disease that causes black spots on clover leaves is Pseudopeziza leaf spot, caused by the fungus Psuedopeziza trifolii. Infections of this disease are most common during cool weather. The black spots are small, round and angular with a reddish tint and white center. The most effective control method for this disease is to simply prune away and discard diseased parts of the clover plant to prevent spreading the infection.
- Black spots associated with sooty blotch, a fungal disease caused by Cymadothea trifolii, have a velvety or shiny appearance. They're most common on white and alsike clover. The black spots will appear mostly on the undersides of the leaves. If the disease is left untreated, these leaves will wither and defoliate prematurely. Treat sooty blotch with approved fungicides or by pruning away diseased parts of the clover.
- Cercospora leaf spot is more commonly called summer black stem, since infections are most frequent in the warm, moist climates in which clover grows naturally. Cercospora zebrina is the disease agent of summer black stem. Depending on where the spots occur, their black color may be tinged by gray, red or brown. Treat summer black stem with an approved fungicide or cultural practices such as harvesting clover leaves early to prevent spread of the disease.
- Spring black stem, or Ascochyta leaf spot, is caused by the fungus Phoma trifolii. Black and brown spots occur along the leaf veins, while larger black spots appear on the stems. Leaves will also wither and defoliate if the disease is not treated. Again, the most effective means of controlling the disease is to harvest clovers early to limit the spread of the disease. Severe infections can be treated with an approved fungicide.
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