September 8, 2017

Red Root Rot​

 

Key Points

  • Red root rot is generally a late-season disease of corn that is most often found in fields with high yield expectations.
  • Premature plant death is common with red root rot and can occur quickly and result in yield losses up to 20 percent.
  • Rotation to other crops, such as soybean or cereal crops, can help break the disease cycle.

What To Watch For

 
Figure 1. Roots showing red coloration from red root rot.

Red root rot is generally a late-season disease; however, it has been found as early as midsilking. Red root rot doesn't develop every year but it can be quite serious when conditions are favorable for development. Plant death near maturity caused by red root rot has resulted in yield losses as high as 20%.1 

Impact On Your Crop

 
Figure 2. Discoloration of basal stalk tissue due to red root rot. Photo source: Steve Koenning, North Carolina State University.

Plants infected with red root rot have roots that are reddish-pink in color and infected plants can easily be pulled from the ground because of decayed roots (Figure 1). The reddish color is similar to that of Fusarium or Gibberella and should not be confused with these diseases. You will need to dig up the plant and look at the fine roots to see symptoms of the disease. Reduced root growth or feeder root development may be evident in addition to the discoloration. Leaves become grayish green and wilted as if killed by frost. The internal tissue of the lower stalk becomes deep red to purple and deteriorates as the plant dies (Figure 2). Plants displaying stalk rot symptoms and those with stalks that are easily collapsed when squeezing are susceptible to lodging. Stalk lodging can occur easily and quickly with strong winds, rain, or other unfavorable harvest-time conditions (Figure 3). Fields should be scouted 2 to 4 weeks prior to harvest to help determine harvest priority. 

Red root rot is most often found in fields with high yield expectations. High plant populations, high fertility, and irrigation are common factors. Moderate temperatures of 75 to 80°F favor plant infection. In many cases, red root rot is a secondary disease that invades the plant after infections from previous diseases, such as Pythium and gray leaf spot. Weakened roots are easier for the pathogen to enter the root tissue. Red root rot has often been problematic in the infrequent cases where corn follows crops of onion. The fungus also causes pink rot of onion; levels of inocula can be particularly high in fields with pink rot.

Tips To Manage

 
Figure 3. Stalk lodging resulting from red root rot.

Disease development varies among seed products. Genetic resistance to red root rot is not common and breeding for resistance is difficult. However, there appears to be some products that are more tolerant to the disease than others. Where red root rot occurs, careful product evaluation can help identify products with multiple genes for resistance. Because the pathogen can overwinter in the soil, rotation to other crops, such as soybean, can help break the disease cycle. Degradation of the infected crop residue is also important for reducing disease inoculum levels.

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Sources:

Sources: 1Compendium of Corn Diseases. 4th Edition. Edited by White, D.G. American Phytopathological Society Press. 1999; Red Root Rot. Field Crop Diseases. University of Illinois. http://cropdisease.cropsci.illinois.edu.; Johnson, G. 2008. Red Root Rot in Corn. University of Delaware. Kent County Agricultural Extension Blog. https:\\extension.udel.edu.
Web sources verified 08/15/2017. 131014060650