To prevent Pythium blackleg, use sterilized pots and potting media. Properly space cuttings, avoid overwatering, and keep rooting media warm. Destroy affected plants immediately.

Bacterial Blight
Bacterial blight is also known as leaf spot and bacterial stem rot. This disease is caused by the bacterium Xanthomonas hortorum pv. pelargonii. Symptoms first appear as small water-soaked spots on the underside of leaves. Within a few days, the spots become well defined on the lower and upper leaf surfaces. The spots are round, sunken, and brown to black in color. Occasionally, plants may show symptoms of wilting along the leaf margins. The leaves usually die from the margins inward in angular patches, which are bounded by veins. Although wilting leaves can be caused by other factors, the angular patches are always associated with the bacterial blight organism. Eventually, infected leaves turn yellow and drop. Bacteria can spread from the leaves, through the petiole, to the plant's vascular (water conducting) system. Infected stems may blacken, shrivel, and rot.

The stem rot phase of the disease is often referred to as "black rot." The exterior of the stem will appear dull and gray, while the interior will have a brown to black discoloration. In cuttings, stem rot may be confused with Pythium blackleg. However, Pythium often kills the plant within a week, while bacterial stem rot progresses slowly, often killing the plant after several weeks.

This disease is extremely infectious and can be spread by physical contact, splashing water, and whiteflies. Use sterilized soil, disinfected cutting tools and pots, and avoid overhead watering. Remove and destroy infected plants. Place cuttings in individual containers. Rotate geraniums in the garden, since the bacterium can survive three months or more in moist soil. Geraniums should not be planted in infected beds for at least one growing season.

Viral Diseases
Geraniums are subject to several different viral diseases. The symptoms will vary, depending on the virus involved and environmental conditions. Symptoms of viral infection include yellow and light green mottled leaves, spotted foliage, light colored veins, leaf distortion, reduced vigor, and increased flower abortion.

Viral diseases on geraniums are usually spread by infected cuttings or seed, and rarely by insects. Symptoms on infected plants may disappear, but cuttings taken from these plants will develop viral symptoms. Infected plants should be destroyed.

P128G
Revised 2/2000
Chad Behrendt, Crystal Floyd