Pesticide interactions in the management of onion maggot, Delia antiqua (Meigen) and onion smut, Urocystis cepulae frost, in Ontario
Onion maggot (OM) and onion smut (OS) are economical pests of onions in Ontario. Efficacy and interaction of combinations of insecticides: chlorpyrifos, cyromazine, tebupirimphos+cyfluthrin, and fipronil; and fungicides: carbathiin+thiram, mancozeb and carbathiin+thiram+mancozeb, were evaluated. Fipronil and cyromazine combinations were most effective against OM, but less effective against OS. Chlorpyrifos and tebupirimphos+cyfluthrin combinations were most effective against OS, but less effective against OM. Chlorpyrifos demonstrated static activity against OS. Fipronil provided best season-long OM control. Best control of OM and OS occurred with carbathiin+thiram+mancozeb combinations. An alternative method to chemical control of OS involving the use of germination stimulants by reduction of soil inoculum also was investigated. Soil applications of dipropyl disulphide (DPDS) and onion juice at 60 L/ha and 120L/ha, in 500 L water, respectively, showed a potential for OS management. The information learned from this study may be incorporated into the existing onion Integrated Pest Management program.