Browning Root Rot, Pythium Root Rot

Pythium spp.

Biology

All spring and winter cereals along with forage grasses can be infected with browning root rot. The rot is caused by one or more Pythium species. This disease was the cause of considerable losses in wheat crops that were grown after fallow in the 1950s. The cause was determined to be low or deficient levels of soil available phosphate.
Fungus spores can remain in the soil and crop residue for five years or more. The spores germinate, invade the roots and cause localized infections. New spores are produced in infected plant parts.

Browning root rot is found in wet soils that have low phosphorus and organic matter levels and a previous history of cereal crops.

Damage Description

This disease occurs in patches. Infected plants become pale green, and lower leaves turn yellow and then brown. Plants are slightly stunted. Diseased plants have fewer tillers, poor root growth and delayed maturity. Soft, wet brown lesions develop on the younger roots near their tips.

Infection during autumn or spring can kill young seedlings, but late season infection usually causes a temporary setback, which may not significantly affect yield.

A few isolated diseased areas in a field may be a warning sign of low amounts of organic matter and low phosphorous availability.

Diagnosis

A soil sample taken according to recommended procedures (that is, cores taken up to 15 cm deep at representative sites in the field) for laboratory analysis will reveal if the phosphorus levels and organic matter content are the cause of the problem.

Management Strategy

• Maintain adequate phosphate levels or balance the nitrogen: phosphate ratio to promote vigorous crop growth.

• Increase organic matter by incorporating straw or manure.