Geranium bacterial leaf spot Xanthomonas campestris pv. pelargonii
IDENTIFICATION — Bacterial leaf spot is sometimes known as bacterial blight, bacterial stem rot or bacterial wilt. No matter what you call it, it’s bad news. This disease has two phases; the first phase infects the leaves and the second infects the stem and roots.
The first symptoms of this disease may not be obvious. They are small, distinct, water-soaked or brown spots on the undersides of the leaves. The leaves quickly wilt, die and may or may not fall off. In some cultivars “V”-shaped yellow or dead areas develop from the margin to the veins.
In the second phase, the bacteria have moved to the water-conducting tissues of the stem and roots. The water-conducting tissues turn brown to black and the roots are blackened although not yet decayed. This leads to the rapid decline of the entire plant.
CONTROL — Prevention is the best policy. This disease is favored by warm and moist conditions with limited air movement. Space plants to improve air circulation, and don’t overhead water – the infection can be splashed in water drops. Remove all plant debris because these bacteria can survive for three to six months. If you take cuttings from your geraniums, sterilize all your tools in a 10-percent bleach solution. Also use sterile containers and potting mix.