Integration of host resistance, disease monitoring, and reduced fungicide practices for the management of two foliar diseases of carrot

Abstract

Commercial carrot (Daucus carota subsp. sativus) producers in Wisconsin and throughout North America rely on repeated fungicide applications to control two foliar diseases caused by Alternaria dauci and Cercospora carotae. New fungicide chemistries, combined with disease monitoring strategies and the incorporation of host resistance, are likely to improve management of these foliar diseases while simultaneously reducing fungicide inputs. An integrated pest management field trial examined the efficacy of combined management practices to control A. dauci and C. carotae, using lengthened fungicide spray intervals. Field scouting and a 1% disease severity threshold for fungicide initiation were combined with four cultivars varying in disease susceptibility and an alternating reduced-input fungicide program. A resistant cultivar, 'Carson', and two moderately susceptible cultivars, 'Gold King' and 'Recoleta', required less fungicide than a susceptible cultivar, 'Fontana', for equivalent disease control. Foliar disease symptoms were observed later in 'Gold King' and 'Carson' than in 'Fontana', allowing fungicide programs to be initiated 1–2 weeks later on these cultivars. In addition, calendar fungicide application intervals could be lengthened from 1 week to 2 weeks without significantly compromising disease control. Integration of a reduced-input fungicide program with cultural management techniques and the benefits of host resistance provided foliar-disease control and root yields comparable with the Wisconsin industry standard of weekly (calendar) fungicide applications.