Powdery mildew of peas is a fungal disease caused by the fungus Erysiphe pisi.
It is a serious disease of field peas, whose infection causes significant yield losses. Severe pod infection can lead to poor seed quality and premature ripening may result in shrunken seeds.
Seeds from infected pods may be discoloured and less palatable, which reduces their market value. Such grains are not fit for consumption.
Crops grown late are more likely to be affected by this disease than early sown crops, and when the disease is severe, the peas become stunted, turn yellow, and defoliate.
BIOLOGY
The fungus over-winters on infected pea trash and produces spores which are blown by wind into new crops to cause infections. Under favourable conditions the disease may completely colonise a plant in 5 – 6 days and once a few plants become infected it rapidly spreads to adjacent areas.
Warm, humid environmental conditions for 4 – 5 days late in the growing season during flowering and pod filling are favourable for the development of powdery mildew disease. Although rainfall is not favourable for the disease, because it washes the spores off plants, dewy nights are sufficient for disease development. The disease may also be seed-borne, although this source of infection may be less important.
SIGNS & SYMPTOMS
All aerial parts of the plant (Leaves, stems and pods) may become infected resulting in withering of the whole plant, but disease symptoms first appear on the upper surfaces of the oldest leaves.
Symptoms consist of a light, greyish, powdery growth on the leaves, pods and occasionally on the stems. This powdery growth is easily rubbed off. As the plant ages, tiny fruiting bodies of the fungus often form in the powdery growth.
Heavily infected foliage turns blue-white in colour and the tissues below these infected areas may turn purple. Severe pod infection can cause a grey-brown discolouration of the seeds. These seeds develop an objectionable flavour which lowers the quality of the grains.
MANAGEMENT
Chemical method
An effective management of the disease can be achieved by use of fungicides which have systemic or translaminar properties, because infection may occur at both sides of the leaves.
Systemic fungicides, however, due to their single site mode of action, are prone to resistance development and the pathogen has the ability to develop resistance to these chemicals. Resistance management can be achieved by alternating several fungicides (with different active ingredients) within a crop’s season.
The following fungicides are recommended for use in control and/or management of powdery mildew on peas;
- ABSOLUTE STAR 400 SC 8ml in 20L
- RANSOM 600WP 12g in 20L
- EXPLORER 3 SL 20ml in 20L
- JUPITER 125SC 15ml in 20L
- CHARIOT 500SC 20ml in 20L
- MILESTONE 250 SC 10ml in 20L
- CADILLAC 800WP 50g/20l (prevention purposes)
- BIODISTINCTION XTRA 700 SC 15ml in 20L (copper-based solution which prevents & suppresses the activity of the fungus).
- AFFAIR TOP 800 WDG 5g in 20L
Non-chemical approaches
- Plant tolerant varieties
- Rotate with non-host crops such as potato, maize, wheat or other grains
- Ensure proper spacing between plants for free air circulation
- Plant crops in rainy seasons because there is less powdery mildew invasion
- Early seeding is recommended because powdery mildew infection is more damaging on late-maturing pea crops.
- Maintain field sanitation/hygiene
- Avoid heavy application of fertilizer.
- Minimize field movements from infected areas to non-infected areas
- Overhead sprinkling may help reduce powdery mildew because spores are washed off the crop.
Tips!
- When using a pesticide, always wear protective clothing and follow the instructions on the product label, e.g. Dosage, timing of application, and pre-harvest interval.
- When spraying, mix the fungicide with INTEGRA 3ml in 20L, which improves the efficacy of the chemical by acting as a sticker, spreader and penetrant.
- Timely control of the disease helps to reduce/prevent losses attributed to its infection.
- A repeat of fungicide spray should be done 1-2weeks.
