Red Rot

  • Symptoms

  • Trigger

  • Biological Control

  • Chemical Control

  • Preventive Measures

Red Rot

Glomerella tucumanensis

Fungus


In a Nutshell

  • Red to brown blotches of different sizes on stalks.
  • Red rotten areas within the white pith.
  • Red oval spots on leaves, particularly visible on the midrib.
  • Grain rot in the form of red, brown or gray discolorations and sour odor.

Hosts:

Sorghum

Maize

Sugarcane

Symptoms

Infected stalks have a dull color and show large red blotches on the surface, more or less important depending on the variety. A longitudinal section of the stalk show red rotten tissue in the otherwise white pith. In resistant plants, the red, diseased areas are often confined to the internodes. As the disease progresses, cavities may form within the pith and bundles of hardened fibers are also visible. Leaves wilt and shrivel. Plants start to emit a foul odor and stalks are easily broken under adverse weather conditions. On leaves, small red oval or elongated lesions develop on the midrib, sometimes along its full length. Sheaths may have reddish patches and small dark spots develop only occasionally on leaf blades.

Trigger

Symptoms are caused by a fungus called Glomerella tucumanensis, which can survive only short periods of time (months) in the soil. Although it is not a true soil-borne pathogen, spores washed into the soil from crop debris may produce infection in recently planted seeds or seedlings. After that, the disease spreads via spores produced in the midrib or stalks of infected plants and transported via wind, rain, heavy dew, and irrigation water. Cool, wet weather, high soil moisture and monocultures favor the disease. Drought also increases the susceptibility of the plant. Besides sugarcane, the fungus can also infect minor hosts such as maize and sorghum.

Biological Control

Hot water bath (for example 50°C for 2 hours) can be used to kill the pathogen on seeds and control the incidence of red rot. Biological control agents can also be used to treat seeds. These include species of fungi of the genera Chaetomium and Trichoderma and some species of the bacteria Pseudomonas. Foliar sprays based on these solutions are also effective in reducing the spread of the disease.

Chemical Control

Always consider an integrated approach with preventive measures and biological treatments if available. Treat seeds with hot water mixed with a fungicide at 50-54 °C for 2 hours to kill the pathogen (thiram for example). Chemical treatments in the field are not effective and should not be recommended.

Preventive Measures

  • Plant resistant varieties, if suitable for your area.
  • Use healthy seeds and seedlings from a certified source.
  • Obtain planting material from fields with no disease.
  • Change sowing time to avoid either too hot or too cool temperatures during the season.
  • Regularly monitor the field and rogue diseased plants or clumps.
  • Avoid the ratooning of diseased crops.
  • Remove any plant debris from the field after harvest and burn them.
  • Alternatively, plow the field several times to expose fungal material in the soil to sunlight.
  • Plan a good crop rotation with non-susceptible plants for a 2-3 years.