Three Alternaria species which are found on leaves and fruit. Isolates related to A. aborescens are mostly associated with leaf blotch. Isolates of A. tenuissima and A. alternata are associated with fruit spot.
Leaf blotch symptoms start as irregular light brown-reddish shaped lesions on the leaves. These symptoms may appear similar to other leaf damage and disease symptoms making diagnosis difficult. Under favourable conditions the leaf blotches will continue to expand and cause severe defoliation due to the spread of the leaf blotch symptoms.
The Alternaria life cycle has some similarities to apple scab because the major source of inoculum is infected leaves on the orchard floor. Bud and twig infections also carry over some inoculum. Alternaria infections are triggered by rain events which cause spore release and spread.
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