Resistant cultivar associated with a disease alert system: a viable way to reduce the number of sprays in controlling downy mildew of onion

Downy mildew is a production limiting factor for Brazil’s main onion producing region. In the present study we tested two management strategies, namely the utilization of a resistant cultivar and the implementation of a disease alert system. Our objective was to mitigate the frequency of systemic fungicide applications while concurrently sustaining optimal yield levels. By carrying out fungicide sprays only when the alert system indicated a severe risk and using the cultivar “SCS379 Robusta”, it was possible to reduce the number of sprays from 11 (calendar) to 5 (alert system), maintaining statistically similar yields (32.58 tonnes/ha – calendar; and 30.76 tonnes/ha – alert system). The reduction in spray applications using an integrated management strategy reduced the cost of spraying by more than half from BRL 0.069/Kg to BRL 0.033/Kg. This study demonstrates that implementation of an integrated management strategy can reduce chemical use and cost without compromising the protection of onion using alert system and more susceptible varieties.