Effects of Postinfection Applications of Ergosterol Biosynthesis-Inhibiting Fungicides on Lesion Formation and Pseudothecial Development of Venturia inaequalis

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Abstract
The ergosterol biosynthesis-inhibiting (EBI) fungicides, bitertanol (150.0 .mu.g/ml), etaconazole (18.7 .mu.g/ml), fenarimol (34.2 .mu.g/ml), and triforine (142.0 .mu.g/ml), applied 120 hr after inoculation of apple (Malus domestica Bork. McIntosh) foliage with conidia of Venturia inaequalis, resulted in the formation of chlorotic lesions 2 wk after application. Some normal sporulating lesions were observed in the bitertanol and triforine treatments after 2 wk and in all fungicide treatments 5 wk after application. Sporulation was also observed around the edges of chlorotic lesions after 5 wk. A postsymptom application of benomyl (150.0 .mu.g/ml) was more effective than the EBI fungicides in reducing the recovery of V. inaequalis on acidified potato-dextrose agar from lesions 5 wk after application. All postsymptom fungicide treatments failed to prevent continued sporulation from treated lesions. Germination of conidia recovered from treated lesions was low compared to that of conidia recovered from untreated lesions. A single postharvest application of the EBI fungicides resulted in the production of fewer pseudothecia in overwintered leaves. Pseudothecia that developed in treated leaves were smaller and contained fewer acospores compared to pseudothecia from untreated leaves. Histological studies indicated that fewer pseudothecia were initiated in treated leaves after leaf fall when EBI fungicides were applied.