Symptoms and Control Methods of Black Stem Rot in Geraniums

Black stem rot of geranium is a disease that occurs on the stems of geraniums, causing the stems to rot and even the whole plant to wither and die.

Symptoms: The disease occurs on both cuttings and mature plants. Infected cuttings begin to rot from the base of the stem, and the rot gradually spreads upward, eventually leading to death. After mature plants are infected, the diseased part turns black and rots, gradually spreading upward, and eventually the leaves fall off. In severe cases, the diseased part girdles the stem, causing the plant to die.

Pathogen: The pathogen is Pythium splendens Braun, a fungus belonging to the phylum Mastigomycotina, class Oomycetes, order Peronosporales, genus Pythium.

Disease cycle: The pathogen survives in the soil as oospores. When conditions are suitable, the oospores germinate and produce germ tubes that invade the host. On susceptible hosts, it produces zoosporangia and zoospores, and the zoospores can cause secondary infection.

Control: 1. Use disease-free branches for cuttings on disease-free seedbeds. 2. When cultivating, change to a new site or replace the potting soil, and disinfect the soil if necessary.