Control insects that carry the fungus spores from one plant to another. Plants should be spaced so that they have plenty of air. Avoid wetting the foliage when watering. Keep greenhouse temperature above 70 degrees F for several days and not below 60 degrees F at night. Where foliage is wet when watering, spray at weekly intervals with recommended fungicide.
Good coverage is necessary for best results.
Some resistant varieties are available. The small black fruiting bodies of the fungus develop on the upper surface of the leaves at the center of the spots. Ash-gray spots covered with the black pycnidia develop on stems. These spots enlarge rapidly and turn dark brown. If the spots entirely encircle the stem, the plants wilt and frequently die.