Rust Management in Green Gram: Symptoms, Identification, Treatment, Chemical, Biological, Natural, and Organic Control

Globally, green gram or mung bean (Vigna radiata) are prone to the common and destructive fungus disease rust. It is caused by the fungus Uromyces vignae and can result in substantial yield declines in the growth of green grams. Small, yellow-orange pustules on the lower leaf surface are the initial symptoms of rust disease; as the condition worsens, they enlarge and change brown. Premature leaf drop is another disease that lowers the plant’s ability to photosynthesize, resulting in stunted growth and decreased yield.

Green gram rust disease management can be done through strategies that combine cultural, chemical, and biological techniques. Planting resistant cultivars, crop rotation, and ensuring proper plant nutrition and spacing are examples of cultural techniques. Fungicides such as azoxystrobin, trifloxystrobin, and propiconazole are used in chemical control.

The use of fungicides should be limited, though, as it could result in the emergence of pathogen strains that are immune to them. Utilizing helpful microbes like Trichoderma harzianum, which can inhibit the growth and development of the rust pathogen, is a key component of biological control. Also, good sanitation practices like clearing and destroying infected plant residue can help prevent rust disease from spreading.

Rust Management in Green Gram

The Causal Organisms of Rust Disease

Rust disease caused by Uromyces phaseoli typica (Syn: U. appendiculatus) is a long-cycle rust that affects several plants, including green gram. It is an autoecious pathogen meaning all spore stages occur on the same host. The disease is characterized by yellowish-brown, unicellular, globose or ellipsoid uredospores with echinulations and chestnut-brown unicellular teliospores pedicellate with warty papillae at the top. The disease also produces yellow pycnidia on the upper surface of leaves and orange cupulate aecia on the lower surface of leaves. Aeciospores are elliptical and unicellular.

The Disease Cycle of Rust Disease

The rust disease cycle starts with the pathogen’s survival as teliospores in the soil and as uredospores in crop debris. Primary infection occurs when sporidia develop from teliospores, while the secondary spread is via wind-borne uredospores. The fungus also survives on other legume hosts.

During the season, the spores produced in the pustules of green gram infect gramma grasses (Bouteloua spp.) around the fields, causing elongated brownish or black spots on their leaves. The spores produced on these grasses infect cotton plants at the beginning of the next season, completing the cycle.

Causes/Conditions Favorable for Rust Disease in the Field

Specific environmental conditions favor rust disease in green gram. The disease-causing spores penetrate plant cells directly, especially in high humidity, moderate to warm temperatures and leaf wetness. The disease thrives in cloudy and humid weather conditions, with temperatures between 21-26°C. In addition, nights with heavy dews provide the ideal environment for the disease to develop and spread.

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Symptoms of Rust Disease

Rust disease in green gram is characterized by circular reddish-brown pustules that appear mainly on the underside of leaves.
The spots are small and numerous, with a pale brown center and reddish-brown margin. The disease can also affect branches and pods, reducing crop yield.
Severe leaf spotting and defoliation can occur during flowering and pod formation, especially under favorable environmental conditions such as high humidity.
When leaves are severely infected, rust pustules fully cover both surfaces, resulting in shriveling and defoliation and significant yield losses.

Rust Disease Yield loss in Green gram

Rust disease in green gram can cause significant yield losses, with severe infections leading to up to 80% crop yield loss. The disease affects plant growth and development, leading to defoliation and reduced photosynthetic activity, which can significantly impact the overall productivity of green gram.

Rust Management in Green Gram by Cultural Method

Cultural practices can help manage rust disease in green gram.
Planting tolerant varieties can reduce the severity of rust infestations.
Removing and destroying infected plant debris can prevent the spread of rust spores.
Crop rotation can also help prevent rust disease by disrupting the disease cycle.

Rust Management in Green Gram by Biological Method

Biological control is an eco-friendly and cost-effective approach to managing rust disease in green gram. Several fungi and bacteria have been found to have antifungal properties that can inhibit the growth of rust spores. These biocontrol agents can be applied to the plant’s roots or sprayed on leaves to prevent and manage rust disease in green gram.

Rust Management in Green Gram by Chemical Method

Fungicides like hexaconazole and propiconazole should be applied 75 days after sowing at 15-day intervals up to 120 days to limit yield losses. Mancozeb at 0.25% can be sprayed before the formation of spores from gramma grass, and Mancozeb 1000g or wettable sulfur 1500g/ha can be sprayed at the onset of disease and ten days later. For severe infestations, Mancozeb 12 kg, Carbendazim 500 g, or Propiconazole 1L/ha can be sprayed immediately on the appearance of the disease and repeated after 15 days.

Rust Management in Green Gram by Organic/Natural Method

Rust in green grams Using organic/natural methods, the essential oils of Corymbia citriodoria (1%), Cymbopogon nardus (0.5%), and Thymus vulgaris (0.3%) have been found effective. These oils can be combined with other natural products to reduce the severity and occurrence of rust.

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Preventive Measures for Control of Rust Disease

Rust is a common fungal disease that can severely affect the yield of various crops. To prevent rust disease in green gram, several measures can be taken. Planting early-maturing cultivars or planting late to avoid rainy seasons can reduce the risk of rust infestations.

Wider row spacing can help the canopy dry faster, reducing the moisture that promotes the growth of rust spores. Regularly monitoring plants is crucial, and any infected plant or weed host, particularly gramma grasses, should be removed promptly. These preventive measures can reduce the incidence and severity of rust disease in green gram and promote healthy plant growth.

Conclusion

Green gram yield decreases due to rust disease can be substantial. The disease can be contained through early detection and prompt management using a variety of chemical, biological, and cultural strategies. Using tolerant varieties in combination with preventative steps can significantly lessen the impact of rust infestations.