Using partial resistance and a disease alert system to reduce the number of sprays to control onion downy mildew

Abstract

Downy mildew is a production limiting factor for Brazil's main onion producing region. In the present study we adopted two management strategies (resistant cultivar and disease alert system) with the aim of reducing the number of systemic fungicide sprays, maintaining satisfactory 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 ton./ha – calendar; and 30.76 ton/ha – alert system). Furthermore, considering only the value of the fungicide, the production cost was BRL 0.069/Kg – calendar, and BRL 0.033/Kg – alert system. Integrated management, using different control strategies, appears to be a viable alternative to mitigate the damage caused by onion downy mildew.