Root Rot Subtly Robs Yield

While an early frost or a lingering drought can cause sleepless nights, it can be hidden challenges that eat away at profits, such as common root rot, a stealthy disease that lingers in fields and can be easily misidentified or undiagnosed.

Because root rot damage is at or below ground level, growers may fail to recognize there is a problem until severe damage has been done. Although instances of significant yield loss are rare, the greatest threat this disease poses is a quiet 5 to 15% yield loss that can go mostly unnoticed year after year. According to North Dakota State University, long-term average yield loss attributed to root rot is around 5% for wheat and nearly 10% for barley across the state.

Identification
Common root rot (Cochliobolus sativus) survives in the soil or in infected debris from previous crops. Because it survives as spores in the soil, it persists longer than other root diseases. Fusarium and Pythium often can cause secondary infections, adding to the disease spectrum and increasing the severity of the disease.

Infection can occur at any stage of plant growth. Symptoms include subtle, elongated brown spots or lesions. Severe infections result in the entire crown, sub-crown internode and root system turning dark brown and dying. Roots may break off easily from severely infected plants. Severe infections are aggravated by hot weather following cool weather, which can lead to a condition called “prematurity blight” where heads frequently appear nearly white. Seeds are shriveled or heads may contain no seed at all.

Root rot is also influenced by water stress. If drought stress increases during the season and is accompanied by relatively high temperatures, root rot will be more prevalent.

“In droughty situations, the root system of infected wheat plants can’t sustain the growth of the plant,” notes Bob Stack, plant pathology professor at NDSU. “In a wet year, even a crippled root system can support the plant. Without rain, roots can’t get moisture, the entire plant will suffer and grain fill is affected.”

Management
Stack says crop rotation is the most important method to control common root rot. “Continuous cereal production favors root rot and therefore has been a concern, especially in central and western North Dakota where continuous wheat crops are more common,” Stack explains.  Rotating to other crops lessens infection levels in the soil. In addition, tillage, appropriate nitrogen levels and good seedling vigor reduce the severity of root rot.

“There are three factors that growers should look at when evaluating root rot – whether the land has been in continuous cereal production, how susceptible are the planted varieties and if the land has a history of root rot. The disease survives better in some soils than others,” he says.

Research shows that a seed treatment (such as Dividend Extreme or other products) can significantly reduce common root rot ratings on plants grown from treated versus non-treated seed, especially under continuous wheat or barley. Seed treatments help protect the root system from diseases such as common root rot, and help improve stand establishment and early season vigor.

More information about common root rot online at http://ndsuext.nodak.edu/extpubs/plantsci/smgrains/pp785w.htm.

The Importance of an Early Start -- NDSU Research at Langdon illustrates the effect of planting date on yield – generally the earlier you can plant, the better.  However, it’s often recommended to use seed treatments with early-planted wheat, to improve stand establishment and seed vigor. Graphics: Terry Gregoire, NDSU Extension Service, Devils Lake.