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Outbreaks of Ascochyta Leaf Blight in Cool Season Landscapes

March 19, 2009
by Lee Butler

Lane Tredway and Lee Butler

Several cases of Ascochyta leaf blight have been observed in tall fescue and Kentucky bluegrass landscapes over the last two weeks. This disease has been observed with increasing frequency over the last few years. The disease seems to be brought on by periods of cool and wet weather in March and April, when these grasses are growing slowly.

Symptoms of Ascochyta leaf blight appear in distinct spots and patches, from 4 to 6 inches in diameter, that are tan or brown in color. In severe cases, the spots may coalesce together into large, irregular areas. On individual plants, the leaves die back from the tip, with the leaf tips becoming shriveled and twisted. Tiny black specks can be seen on the infected leaves - these are fruiting bodies produced by the fungus.

The good news is that this disease rarely causes severe damage to tall fescue or Kentucky bluegrass. Because it only infects the leaf tips, the turf will recover very quickly once the weather becomes favorable. 

Ensure that adequate fertility has been applied to speed up this recovery process.

Fungicides are rarely necessary to control Ascochyta leaf blight, and little information is available on which fungicides are effective. 

Products containing mancozeb (Fore, Dithane) and iprodione (26GT, Iprodione Pro) may be effective if the damage reaches unacceptable levels.