Reduce shade and improve soil aeration and water drainage. Avoid dry spots, over fertilizing with nitrogen, and maintain as high a cutting height as possible. Avoid prolonged leaf wetness by irrigating in pre-dawn, or early morning hours. If possible, increase air movement. 

Follow good management practices to prevent the development of leaf spot. Fungicides are usually not warranted.

Cultural control

Reduce shade and improve soil aeration and water drainage. Avoid dry spots, over fertilizing with nitrogen, and maintain as high a cutting height as possible. Avoid prolonged leaf wetness by irrigating in pre-dawn, or early morning hours. If possible, increase air movement.

Treatment decisions

Leaf spot usually is not serious enough in most places to warrant the use of fungicides although they may be used where leaf spot is severe. On landscape plants remove all affected parts and rake up and discard or burn any leaves that have already fallen to reduce the chance of re-infecting the plant again. This is especially true with rose bushes.

After removing all infected leaves, apply a fresh mulch around the base of the plant to reduce the chances of the fungus being splashed up on the leaves during rainfall or watering.