Autumnapplied urea and other compounds to suppress <i>Venturia inaequalis</i> ascospore production

Abstract

The effect of urea applied to apple leaves in autumn on production of ascospores of Venturia inaequalis (black spot) was quantified in four studies Autumn urea at concentrations from 020 reduced ascospore production in spring in proportion to the log of the urea concentration A single application of 5 urea sprayed onto fallen leaves gave an 88 decrease in ascospore production Urea applied to apple trees before leaf fall significantly reduced black spot disease on leaves the following spring in cv Fuji but not in cv Royal Gala Ascospore production was reduced by the fungicide cupric hydroxide but was not affected by a low concentration of fish fertilizer Three methods of ascospore assessment were used to detect differences in ascospore production