Susceptibility of Apple and Pear Varieties to Damage by Certain Organic Fungicides

Abstract

Fungicide programmes, designed to control both scab and mildew, have been compared for phytotoxicity in several seasons on apple and pear varieties. Dodine acetate was found to cause russeting of the fruits of several apple and pear varieties. In one year, frost at a spraying time seemed to interact with dodine acetate application to produce unusual russet on Sunset apples. Crops of Conference and of Doyenne du Cornice pears were reduced in some years when dodine was applied. The fungicide based on nitrated octylphenols, DNOPC, caused no undesirable effects on the apple varieties, but tended to reduce cropping on pears; the effects of the unesterified mixture, DNOP, were more serious. Both dodine acetate and DNOPC caused reductions of fruit bud formation on Cornice, an effect already reported for organomercurial fungicides on Conference and for didecyldimethylammonium bromide (DDAB) on both varieties. It is suggested that freedom from this effect should be a criterion to be satisfied in the evaluation of any new pesticide for pears.