Red root rot has been a problem in the Atlantic coast states since the late 1980s and has increased incidence in Colorado, Nebraska, Missouri and Oregon since the late 1990s. Yield losses as high as 15 to 20 percent have been reported in the Delmarva region. In addition to the yield losses are the losses due to harvest difficulties as a result of the root lodging.

Red root rot is caused by a complex of soil fungi that includes Phoma terrestris, Pythium species and Fusarium species, of which Phoma terrestris is the primary pathogen. The optimal temperature range for disease infection is 70 to 80 degrees Fahrenheit around the time corn begins to senesce. High plant populations, high fertility and irrigation can be common ingredients in infected fields.

Red root rot symptoms typically appear just before senescence. Roots and basal stalk tissue (lower three internodes) infected with red root rot have a reddish-pink discoloration. Roots become a deeper red color as the disease progresses. The reddish coloration can be confused with Fusarium or Gibberella stalk rots, but red root rot has a darker red color. The root tips and roots may be shredded or frayed, similar to insect damage. The root mass can be small, making severe lodging more likely. Combining may be difficult because the entire root ball may be pulled up as plants are harvested. During the late stages of ear filling, the disease can cause rapid, premature death of the plant. Foliar symptoms can occur over a four to five day period and plant death of the most susceptible plants can occur within a week. Other above ground symptoms include a grayish green discoloration of leaves and stalks or a wilted appearance, which is also characteristic of other stalk rot diseases.

Management options for red root rot are limited. Crop rotation with a non-host such as soybean can provide some control. Environmental stress during the season may contribute to disease infection and severity so minimizing stress throughout the season will be beneficial. At present there is no specific resistance to red root rot available in current hybrids but hybrids do vary greatly in the rate of disease development. The problem with developing resistant hybrids is that the inheritance of resistance is a polygenic trait with additive gene action, which complicates the breeding and selection efforts. This is in addition to the difficulties of screening the material to detect resistance. The conditions of the occurrence of the disease and the combination of organisms involved in the disease makes screening for the disease resistance difficult.

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