What Are the Causes of Damping-Off in Begonias?

Black Root Rot

• Established begonias can fall victim to damping-off caused by black root rot. This disease is caused by fungi present in the soil, and can be controlled by planting your begonias in acidic soil. Symptoms of black root rot include dry areas of brownish discoloration on roots occurring where lateral roots meet the tap root. These diseases may also affect tubers in tuberous begonias. Black root rot fungi can live up to 10 years in affected soil. Monitoring the pH of soil is helpful for preventing or controlling fungi causing damping-off in begonias. As you water your plants, their soil becomes increasingly alkaline, which promotes the growth of fungi causing rot and related diseases.

Phytophthora Root Rot

• Phytophthora root rot affects the roots of seedlings and established begonias. Unlike black root rot, phytopthora root rots cause affected roots and stems to deteriorate with moisture-soaked brown or black rot. The causal agent is a fungus that enters begonias through the root tips; it can survive for years in soil and plant debris. Removing dead leaves and debris helps with controlling this fungus. The symptoms of phytophtora infestation resemble those of pythium, a group of fungi also causing damping-off, root, and stem rot in begonias.

Pythium

• Overwatering encourages pythium fungi to flourish. This type of rot is wet, but odorless. It typically occurs in cool, damp soil. Visual symptoms include a wet brownish to black rot that destroys lower stems, roots and tubers. Pythium spores thrive in soil and plant debris; keeping your garden areas clear of debris promotes air circulation that dries soil surrounding your begonias. Soggy soil is a primary cause of pythium fungus infections in begonias; fungi spores can be transferred by water flowing from one plant to another.

Prevention and Treatment

• The longevity of fungi causing damping-off in begonias and the fungi's presence in soil and plant debris make eradicating them unlikely. Providing enough room between seedlings and root cuttings is helpful for controlling plant diseases causing damping-off. Clean gardening tools in a solution of 1 part bleach to 4 parts water for avoiding fungal contamination between plants; apply fungicides to plants via spray or drenching their soil. Ask a local nursery or your state's cooperative extension service for recommendations for using fungicides. Fungicides contain hazardous chemicals and should not be used on seedlings or in areas accessible to children, pets and wildlife.