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

Sorghum rust is a fungal disease of sorghum and other grass species. This disease is one of the most serious diseases of sorghum and can cause significant yield losses. It is an economically important disease in many parts of the world, especially in subtropical and tropical regions.

Sorghum producers must understand the disease cycle, its environmental interaction, and risk factors to prevent and manage this disease. Control measures for sorghum rust include good crop management practices, using resistant cultivars, and applying fungicides. This article will provide an overview of sorghum rust disease, including its symptoms, biology, and control.

Rust Disease Management in Sorghum

The Causal Organism of Sorghum Rust Disease

Puccinia purpurea, a member of the family Pucciniaceae, an obligate parasite, has a wide host range, which means it can infect many different sorghum species.
The uredospores are deep brown, pedicellate, ellipse, or ovoid, with thin walls and spiny edges.
The teliospores are bi-cellular, spherical at the peak, and range between red to brown. Every cell consists of one germ pore. Teliospores grow into promycelium and basidiospores on germination.
The alternative host, Oxalis corniculata, is infected by basidiospores, on which pycnial and aecial phases develop.

The Disease Cycle of Sorghum Rust Disease

Uredinia, small, raised, reddish-brown pustules on plant leaves, start the cycle. Uredinia have haploid urediniospores and diploid teliospores.
These spores can survive for months or years, enabling the fungus to overwinter and stay dormant until the next growing season.
Telia, bigger, darker pustules on an infected plant stem, form in the second stage.
Telia has two teliospores. These spores survive longer than urediniospores.
Teliospores germinate, and basidia, spore-producing structures on the telia’s upper surface, form in the third stage.
Haptloid basidiospores from basidia invade healthy plants.

Mode of spread and survival of the pathogen in sorghum crop

Insects, wind, or rain spread fungal spores, infecting crops anytime.
Uredospores remain inert in soil and plant residues for longer.
Oxalis corniculata, an alternate host, helps perpetuate the fungus.

Causes / Conditions Favorable for Sorghum Rust Disease Spread in the field.

Rainfall – The rainy weather condition facilitates the disease incidence.
Temperature – Cooler temperatures of 10-12 °C facilitate teliospores’ germination.

Symptoms of Sorghum Rust Disease

Sorghum Rust Disease causes severe defoliation, reduced grain quality, and yield losses.
The disease is characterized by yellow-orange pustules or spots on the leaves, stems, and other parts of the plant, which can turn brown and eventually become powdery.
The presence of small flecks on lower leaves and reddish powdery masses of uredospores. The pustules or spots may also be present on the leaf sheaths and the stalks of inflorescence.
The leaves may also become distorted, and the grains may be affected. In severe cases, the plant may die completely.

Percentage of yield loss due to Sorghum Rust Disease in Sorghum crop

The yield losses caused by sorghum rust can be significant. The percentage of yield loss due to the disease can range from 5-30%.
Yield losses may be higher in areas with more severe diseases, such as in certain parts of Africa and India.

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Diagnosis of Sorghum Rust Disease in Sorghum crop

The first step in diagnosis is to examine the leaf for rust spores.
The next step is to identify the species of rust by collecting and examining samples of the rust spores under a microscope. Depending on the species, the spores may be single, clustered, or cylindrical.
Once the species of rust has been identified, the next step is to determine the severity of the disease. It is done by measuring the size of the lesions and the number of pustules present.

Cultural Control Measures of Sorghum Rust Disease

Sanitation: It involves removing crop residues from the field and cleaning equipment after harvest to reduce the number of spores and fungi available to cause infection.
Crop rotation involves planting sorghum in a field not planted with the same crop the previous year. It reduces the number of spores and fungi available to cause infection in the sorghum crop.
Variety selection: Growing resistant sorghum varieties can help reduce the impact of Sorghum rust disease. Varieties resistant to the disease are available and should be selected for planting.
Alternative host: Removal of the alternate host Oxalis corniculata prevents the perpetuation of the disease in the crop.
Roguing out: Removing and burning the infected plants is necessary to prevent the spread of this disease throughout the field.

Biological Control Measures of Sorghum Rust Disease

Biological control uses natural enemies such as the fungus Trichoderma harzianum, which acts as a natural fungicide. When applied to the sorghum plant, the fungus produces antifungal compounds inhibiting the rust fungus, reducing its spread and severity. Another beneficial organism that can be used is the nematode Steinernema carpocapsae, which feeds on the rust fungus and is known to reduce its spread.

Biological control is not a one-time solution but requires regular monitoring and maintenance. Additionally, the beneficial organisms must be regularly reapplied to ensure that the rust fungus does not gain a foothold in the environment.

Chemical Control measures of Sorghum Rust Disease

Generally, Mancozeb is sprayed at a concentration of 2 kg/ha.
The most common fungicides used for rust control in sorghum are triazoles, strobilurins, and mancozeb.
Triazoles are a class of fungicides that inhibit the synthesis of an enzyme necessary for producing fungal cell membranes.
Strobilurins are a class of fungicides that act by disrupting the production of energy in fungal cells.
Mancozeb is a fungicide that prevents the production of spores, which are the main cause of the spread of rust in sorghum.

Preventive Measures for Control of Sorghum Rust Disease

Monitor fields regularly – Monitoring fields for signs of disease will help catch and manage it early before it spreads.
Choose disease-resistant varieties – When selecting sorghum varieties, choose those resistant to rust.
Practice crop rotation – Rotating sorghum with other crops such as corn, soybeans, or wheat helps reduce the risk of sorghum rust.
Practice good sanitation – Sanitation is key to preventing the spread of sorghum rust.
Use Fungicides – Appropriate fungicides are mandatory for proper disease control.

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Conclusion

Strategies for preventing and managing the disease Finally, it is important to remember that sorghum rust is a highly dynamic disease and that its management strategies must be continually monitored and adapted to ensure successful management in the future.

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

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