Agriculture

Leaf Blight Disease Management in Sorghum: Symptoms, Treatment, Chemical, Biological, Natural, and Organic Control

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Sorghum leaf blight is a fungal disease that causes substantial mortality in tropical and subtropical areas. It is a major sorghum disease in India and other nations. In the past, the disease has resulted in substantial yield declines in sorghum. It remains a significant danger. To avoid and control this disease, sorghum producers must comprehend the disease cycle, its interaction with the environment, and risk factors.

Leaf Blight Disease Management in Sorghum

Cultural techniques such as crop rotation, thorough plowing, and the use of disease-resistant cultivars, as well as chemical treatments, are used to control the disease. This article will summarize sorghum leaf blight, including symptoms, biology, and control.

Leaf Blight Disease Management in Sorghum

The Causal Organism of Sorghum Leaf Blight Disease

  • Exserohilum turcicum, previously known as Helminthosporium turcicum, an obligate plant pathogen, causes leaf blight disease in sorghum. It will develop mycelium that is limited to the infected lesions.
  • Conidiophores arise via stomata and are simple in structure, olive green, septate, or compartmentalized and geniculate.
  • Conidia are olive green or brown, containing 3-8 septa, and are thick-walled.
  • The pathogen is also capable of causing seed rot and seedling blight in sorghum.

The Disease Cycle of Sorghum Leaf Blight Disease

  • The fungus begins as microscopic spores that propagate via breeze and water. When spores settle on a sorghum plant, they germinate and penetrate it via the stomata (leaf openings).
  • The fungus colonizes the plant, creating a mycelium and developing inside the leaf tissues.
  • This mycelium creates toxins that cause the disease’s signs, such as yellow-brown lesions on the leaves and stalks.
  • The lesions become darker as the illness advances and can extend to other areas of the plant.
  • The fungi also create fruiting bodies, which discharge spores back into the environment, thus continuing the infection cycle.

Mode of Spread and Survival of the Pathogen in Sorghum Crop

  • Wind-borne ascospores spread the disease and can survive in the atmosphere for several weeks.
  • Seed-borne conidia, responsible for the seedling infection, are the main means of disease transmission.
  • Secondary disease spread occurs via wind-borne conidia, and the pathogen that survives in contaminated plant residues is another cause of disease spread.

Causes/Conditions Favorable for Sorghum Leaf Blight Disease Spread in the Field.

  • High Rainfall & Humidity – In the atmosphere, approximately 90% humidity and high rainfalls can spread the disease.
  • Weather – Cool and moist weather will increase the intensity of the disease incidence.

Symptoms of Sorghum Leaf Blight Disease

  • Leaf chlorosis, early defoliation, and stalk rots are symptoms of the disease.
  • The disease is distinguished by tiny, brown spots on the foliage encircled by a yellow halo, after which the leaves turn yellow and die out.
  • In its early stages, the infection appears as slight, extended, thin patches that eventually spread throughout the base of the leaves.
  • On mature plants, the clinical signs are massively elongated diseased patches with darkened edges that are straw-colored in the middle.
  • Once the spores are released, the straw-colored area turns black.
  • Many patches that form and merge on the foliage could destroy significant portions of fresh leaves, leaving the plant with a burned impression.

Percentage of Yield Loss Due to Sorghum Leaf Blight Disease in Sorghum Crop

  • Overall, the percentage of yield loss due to sorghum leaf blight disease can vary greatly depending on environmental conditions, crop management practices, and the implementation of control measures.
  • In severe cases, yield losses can reach up to 50% of the crop planted.

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Millet Field

Diagnosis of Sorghum Leaf Blight Disease in Sorghum Crop

  • The first step in diagnosing sorghum leaf blight disease is observing the affected plants’ symptoms. If the leaves have yellow-brown lesions, leaf spots, or holes, the plant is likely infected with Exserohilum turcicum.
  • The plant should be inspected for fungal spores or hyphae to confirm the diagnosis. If present, the spores or hyphae can be collected and analyzed under a microscope to confirm the presence of the fungus.
  • Once the fungus is confirmed, additional steps can be taken to diagnose the severity of the disease. For example, a soil sample can be taken to determine the fungus population in the soil.
  • Additionally, a leaf sample can be taken to estimate the amount of infection on the leaf. The infection can be measured by counting the number of lesions or spots on the leaf.

Cultural Control Measures of Sorghum Leaf Blight Disease

  • Sanitation involves removing infected plants and residue from the area and decreasing the number of overwintering hosts.
  • Crop rotation reduces the number of pathogens in the soil and the frequency of crop disease.
  • Planting resistant types are one of the most effective ways of controlling SLB, as some variations are more immune to the illness than others.
  • Planting disease-free seedlings reduces the chance of agricultural infection.
  • To avoid spreading this illness, infected plants must be destroyed and burned.

Biological Control Measures of Sorghum Leaf Blight Disease

  • Fungi such as Trichoderma, Gliocladium, and Penicillium species can cover the surface of sorghum stalks and fight for resources with the pathogen. They also generate antibiotics and other substances that can inhibit the pathogen.
  • Bacteria used for biological control create enzymes that degrade pathogen cell wall components, stopping the pathogen from colonizing the plant. They can also generate compounds that prevent pathogen development.
  • Bacillus subtilis and Pseudomonas fluorescens are two microorganisms that have been used. Viruses also control sorghum leaf rot. These viruses infect and destroy pathogens, limiting their capacity to cause disease.
  • Viruses that have been used include the bacteriophage phiX174 and the bacilliform virus. In addition to these helpful microbes, other microbial products can be used.
  • Chitinases, glucanases, and proteases are examples of these enzymes. These enzymes can degrade the pathogen’s cell wall and other components, decreasing its capacity to cause disease.
  • However, it should be noted that this strategy’s success depends on the correct selection and implementation of beneficial microorganisms and their related microbial products.

Chemical Control Measures of Sorghum Leaf Blight Disease

Seed Treatment – Treating seeds with fungicides Captan or Thiram at 4 grams/kg of seed.

Apply fungicides such as Mancozeb at 1.25 kg/ha or Captafol at 1 kg/ha at the start and middle of the season.

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Millet Plantation

Preventive Measures for Control of Sorghum Leaf Blight Disease

  • Avoiding Overcrowding: A large number of sorghum plants in a single field increases the chances of infection. Therefore, it is advised to avoid overcrowding the sorghum field.
  • Proper irrigation of the field helps reduce the chances of infection.
  • Early Detection: Early detection of the disease can help to take preventive measures in time.

Conclusion

Sorghum Leaf Blight is a major problem in many parts of the world, particularly in Africa, South Asia, and the United States. In some countries, the disease can cause up to 40% yield loss in sorghum crops. To reduce the losses caused by sorghum leaf blight disease, farmers should practice good crop management, such as avoiding overcrowding, rotating crops, and controlling weeds. Additionally, fungicides may be used to control the spread of the disease by using a proper approach toward the crop.

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Author: Reddy

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