Key Features
- Stunting and yellowing
- Leaf scorch, browning edges
- Brown roots and lower stem
Symptoms
Pythium is regularly found in soil and decomposing vegetation. The first symptoms of Pythium infections include stunting, yellowing, and dieback. A soft, watery rot may develop or a covering of fine, white mycelium may be seen on the crown and lower stem infections. Careful examination of the root system will show dead tips, wet-looking soft roots, and the outer layer of some roots falling off. This is not a conclusive symptom, but one to note. These symptoms can also be caused by other soil-borne pathogens as well as drought or poor soil fertility. Sending root samples to a plant disease diagnostic lab is the best way to determine which root rot pathogen is causing the damage.
Biology
Pythium grows, infects, and colonizes a plant much like a fungus. However, they aren't true fungi, so they are not controlled by most fungicides available to homeowners! Pythium survives as soil-borne spores in the absence of a host. Swimming spores are produced in warm, wet soil and are capable of moving short distances towards plant roots while the soil is wet. Pooling or flowing water allows these spores to move far greater distances. Infection is through root tips or wounds at the soil line. Seedlings, new transplants, and stressed plants are most at risk. Vigorously growing, established plants are relatively resistant to the disease. All Pythium species favor wet conditions and high soil soluble salts.
Management Recommendations
Accurately diagnosing this disease is essential because fungicides labeled to control other root rot pathogens (such as Thielaviopsis, Fusarium, or Rhizoctonia) will not be effective against Pythium root rot. Poorly drained soils, over watering, and plant stress are the most common factors driving Pythium root rot. Increase soil drainage through soil amendments or install drain tile in clay soils. Water and fertilize to meet, but not exceed the needs of the plant. Pythium diseases are also more severe on over-fertilized plants. No general use chemicals are currently labeled for Pythium control. If cultural methods do not control the disease, host plants may need to be replaced with non-host species.
Effective Pesticides
Pesticides are neither available nor recommended for managing this disease.
Resources
