Petal blight is more severe in cool, moist springs. Petal blight is caused by an airborne fungus which over-winters on the spent flowers. Remove old mulch and replace with new in early spring. Drench soil area under plants with Terracolor in January. Spray with Thylate or Benomyl when blooms begin to open.
Good coverage is essential.
Bayleton may be used when the buds show color. See ovulinia petal blight for a more detailed discussion. The undersides of the leaves become discolored by excrement and cast skins. Repeat application every 10 days until control is obtained. Chlorosis Leaves turn light green to yellow, then creamy white between the veins, while the veins remain green.