Phoma
Phoma Cycle
Symptoms
These first appear in the autumn as pale brown, white or greenish leaf spots (5-20mm in diameter) which contain many ‘pin-head’ black spots called pycnidia. Infection can occur anytime from crop emergence, but is commonly seen from 2-4 leaves onwards; the earliness of infection is related to the rainfall during August.
The infection grows down the leaf petiole and infects the stem. Subsequently, brown lesions (cankers) appear in the late spring, associated with the leaf scars at the stem base.
These gradually enlarge, may girdle the stem and cause premature ripening and lodging.
Control
Strategies involve cultivations to bury crop residues before emergence of the new crop, use of resistant varieties and fungicide sprays. The spray threshold for Phoma is when 5 -10% plants are infected with at least one lesion.
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