| Onion thrips (OT), Thrips tabaci Lindeman, is a serious pest of onion. In recent years, Ontario onion growers have experienced economic losses and severe control problems due to this pest. In 2000, this project was initiated to create a comprehensive OT-management program for growers. In order to develop such a program, a better understanding of OT biology, the effectiveness of currently available control agents and the potential of replacement control tactics was required.; Based on monitoring research, adult OT were captured on white sticky traps placed in commercial onion fields in Thedford-Grand Bend Marsh as early as mid-May in 2001, 2002 and 2003. However, OT were not recorded on plants in the monitored fields until late June to early July. Pole trap monitoring revealed that the majority of OT fly within 0.5 m of the plant canopy. However, thrips were captured on traps as high as 4.95 m above the canopy.; Ontario growers are concerned about the efficacy of recommended insecticides. In 2001, six of eight field-collected OT populations were resistant to lambda-cyhalothrin, five were resistant to deltamethrin and three of four were resistant to diazinon. In 2002, nine of 12 field-collected populations were resistant to deltamethrin and seven of 11 populations were resistant to diazinon. In 2003, 15 of 16 field-collected populations were resistant to both lambda-cyhalothrin and deltamethrin while six populations were resistant to diazinon. Laboratory experiments revealed that thiamethoxam, imidacloprid, fipronil and spinosad were effective alternatives.; Foliar trials in both commercial onion and research fields revealed that spinosad, acephate, novaluron and pyriproxifen significantly reduced OT populations. Field trials revealed that imidacloprid as a seed-, planting-water- or tray-drench treatment delayed the development of OT populations.; Onion thrips tend to congregate deep within the axils of onion leaves making delivery of control agents difficult. Track and field sprayer trials revealed that the TeeJetRTM XR8004 flat fan nozzle provided the best coverage of inner onion leaves. Coupling treatments with Sylgard RTM 309, an organo-silicone non-ionic surfactant, at 200 L/ha significantly increased inner onion leaf coverage. The use of non-ionic surfactants Agral RTM 90 or LI-700RTM also increased coverage of inner onion leaves. |
