EFFICACY OF REDUCED-RATE INSECTICIDE APPLICATIONS FOR THE CONTROL OF THE CARROT FLY (PSILA-ROSAE F) IN NEW-ZEALAND

Two field experiments were conducted in 1993-94 to investigate the eff icacy of the insecticides phorate, diazinon and furathiocarb at field rates and at a range of lower rates for the control of carrot fly larv al damage. Phorate granules drilled with the seeds effectively control led the first generation larvae, even at one third the recommended rat e (0.73 kg a.i./ha); recommended (2.2 kg a.i./ha) and half rate were e qually efficient in controlling second generation larvae. Third genera tion damage (the most important economically) was not significantly re duced by any rate of phorate granules applied at drilling. Phorate app lied as mid- or late-season granules gave better control of second-gen eration damage, even at half rate, than did full rate at drilling. The furathiocarb seed-coated treatment at 4% (40 g a.i./kg seed) controll ed the first generation damage, but had no significant effect on the s econd generation. Furathiocarb seed coated at 2% (20 g a.i./ha) did no t prevent either first or second generation damage. This crop was harv ested before third generation damage occurred. A diazinon midseason sp ray controlled third generation damage at field rate (0.8 kg a.i./ha) but not at half, one third and one eighth field rates. Prospects for t he reduction of insecticide rates in New Zealand carrot crops are disc ussed with reference to these and other methods.