A distinguishing characteristic of X. pelargonii stem rot, slimy bacterial ooze exuded from a cut stem, is never associated with Pythium blackleg. Disease Development X. pelargonii is commonly introduced into the planting medium on cuttings taken from infected plants. There is also some evidence which suggests that the pathogen might be seed transmitted. The bacteria can spread through the rooting medium to healthy cuttings if plants are being rooted close together and the moisture level is high. The pathogen is frequently spread by contaminated tools and by physical contact between blighted and healthy leaves.
Bacteria can enter a plant wherever wounds occur.
Once X. pelargonii is inside the host, it spreads through the vascular system producing the stem rot and leaf symptoms. When the temperature becomes elevated, symptoms normally associated with X. pelargonii develop. Generally latent infections will occur when geraniums are grown at or below 68 degrees Fahrenheit. Latent infections might be expected in geraniums grown as house plants, especially when they originate from cuttings taken in late summer or fall. The cooler fall and winter temperatures may prevent symptom development until the following spring.