Pea
Blackspot of Field Pea
Mycosphaerella pinodes and Phoma medicaginis var. pinodella
Fungus
In a Nutshell
- Spotting of leaves and pods.
- Occurrence of irregular shaped dark brown to black lesions or flecks on infected leaves and pods.
- Sunken brown or purple-black discolouration.
Can also be found in
Pea
Symptoms
Blackspot causes lesions on the stems, leaves, pods and seeds. Under humid conditions, early symptoms are commonly observed under the plant canopy, on the lower leaves and stems. Irregularly shaped small, dark brown spots are found dispersed on the leaf surface. Under continued humid conditions, the spots enlarge and coalesce, causing the lower leaves to become completely blighted. Lower stem lesions appear as purplish-black streaks, which can cause rot at the plant base leading to crop lodging. Spots on pods are purplish-black and can merge to develop sunken areas. Infected seeds can be discoloured and look purplish brown.
Recommendations
Organic Control
Cultivate resistant varieties.
Chemical Control
Always consider an integrated approach along with preventive measures and available biological treatments. It is recommended that all pea seeds be treated with a fungicide like mancozeb.
What caused it?
Damage is caused by the fungus Mycosphaerella pinodes, Phoma medicaginis var. pinodella which may either be seed-borne, soil-borne or survive in pea trash. The disease usually becomes established when fungal spores, produced and stored on old pea stubble, are carried into the new crop by the wind. Infection may occur at any stage of plant growth. Spores produced on infected plants are transferred onto adjacent healthy plants by wind and rain splash. The disease can also become established by the sowing of infected seeds. During wet weather, the disease may spread rapidly. In a dry year, the planting of infected seeds may not produce a diseased crop, but under wet conditions severe disease is likely. The fungi can survive in the soil for several years.
Preventive Measures
- Practice clean cultivation.
- When planting, aim for the separation of at least 500 m from last year’s pea paddock.
- Avoid using old or damaged seeds that can reduce seedling vigour and increase susceptibility to infection.
- Avoid early sowing at high seeding rates as this increases the exposure of pea seedlings to the pathogens and produces crops with a large canopy, increased lodging and high humidity; all of which increase the risk of developing the disease.
- Practice crop rotation whenever possible.
- Peas should not be grown in the same paddock more than once in 3 years.
- If the disease occurs, the rotation should be extended to 1 in 4 or 5 years.
- Destroy infected pea trash and self-sown plants by grazing and burning.
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