Green gram powdery mildew is a fungal disease caused by the fungus Erysiphe polygoni.
It is one of the widespread diseases of several legumes in green gram with a characteristic symptom of whitish, superficial, powdery fungal growth, mainly on leaves.
Infection not only causes the foliage to curl and distort making it unsightly but the fungus also lowers photosynthetic efficiency that results in reduced plant growth and vigour.
DISEASE CYCLE
- polygoni is an obligate parasite and survives as cleistothecia in the infected plant debris. Primary infection is usually from ascospores from perennating cleistothecia, and the secondary spread is carried out by the air-borne spores. Rain splash also helps in the spread of the disease.
Unlike many other fungal diseases, extended periods of leaf wetness are not necessary for the germination of spores, and therefore the disease is often a problem during dry weather conditions.
High humidity is favourable for spore production and infection, and crops growing in areas with poor air flow, which allows the accumulation of humid air, are likely to be attacked. Plants grown in these situations are also more likely to experience dry soil, which is another factor that increases susceptibility.
After landing on the plant tissue, a spore of E. polygoni germinates, enters a stoma and then grows. Fruiting bodies grow out of the stomata and release spores into the air, to be carried to other plants or plant parts, causing infections.
It takes about a week from the time of infection to development of symptoms on the crop
SYMPTOMS & SIGNS
These are usually easier to identify because powdery mildew forms patches of whitish mycelium on upper and lower leaf surfaces, petioles, and stems.
- White powdery patches appear on leaves and other green parts which later become dull coloured
- These patches gradually increase in size and become circular covering the lower surface also
- When the infection is severe, both the surfaces of the leaves are completely covered by whitish powdery growth
- Infected leaves also show necrotic symptoms.
- In severe infections, foliage becomes yellow causing premature defoliation
- Diseased plants are stunted, mature late and produce very few flowers and pods.
- Pods of infected plants are reduced in size and turn yellow in colour.
- The disease also creates forced maturity of the infected plants which results in heavy yield losses.
DISEASE MANAGEMENT
Strategies for the control of the disease involve an integrated approach using a combination of several practices.
Healthy and vigorous plants grown under a good nutritional program and suitable sanitary conditions are less susceptible to powdery mildew infection than plants under stress.
Chemical control
A successful fungicide program requires controlling the pathogen on both leaf surfaces. This can be achieved by use of fungicides with systemic or translaminar properties.
Systemic fungicides, due to their single site mode of action, are prone to resistance development and the fungus has the ability to develop resistance to these fungicides. Resistance management can be achieved by alternation of several fungicides within a crop’s season.
The following fungicides are recommended for use in control and/or management of powdery mildew on green grams;
- ABSOLUTE 375SC 10ml/20l
- RANSOM 600WP 15g/20l
- EXEMPO CURVE 250SC 15ml/20l
- EXPLORER 3 SL 10ml/20l
- CHARIOT 500SC 20ml/20l
- MILESTONE 250SC 10ml/20l
- JUPITER 125SC 15ml/20l
- TOMAHAWK 250EC 10ml/20l
- MEGAPRODE LOCK 525WP 30g/20l
Spraying the crop with BIODISTINCTION XTRA helps in preventing and suppressing the activity of the fungus.
Non-chemical control
- Use resistant varieties
- Ensure a proper crop spacing to promote free air circulation
- Ensure field sanitation/hygiene, e.g. by removal of affected plants and debris
- Choose planting sites with good air movement and free of shade.
- Practise rotations with non-host crops
- Minimize field movements from infected areas to non-infected areas
- Avoid overhead irrigation to keep foliage dry
- Ensure a regular plant nutrition to encourage strong growth
Note;
- Whenever spraying, mix the fungicide with INTEGRA 3ml/20l, which improves the efficacy of the fungicide by acting as a sticker, spreader and penetrant.
- Timely control of the disease helps to reduce/prevent losses attributed to its infection.
- Fungicides should be reapplied after 1-2weeks.
