Bacterial blight is most serious on white flowered varieties. The young shoots develop black stripes or one side of the shoot turns black. Spots develop on the leaves, forming a water-soaked blotch.
Young leaves turn black and die quickly.
On older shoots, the spots enlarge more slowly. The flowers wilt and darken. The disease is worse when wet weather occurs as the new shoots are developing. Thin plants to increase air circulation. Remove and destroy diseased shoots and avoid excessive nitrogen fertilizer.