Management of Heliothis punctigera on field peas in south-eastern Australia

Abstract

Cypermethrin was found to be an effective substitute for DDT in controlling Heliothis punctigera in field peas. A single spray of cypermethrin prevented significant damage by larvae to field peas in trials in South Australia and Victoria over 3 seasons. Endosulfan was not as effective as cypermethrin. Bioassays of leaf discs dipped in cypermethrin showed that residues of 0.1 mg a.i. kg-1 caused 50% feeding inhibition, 0.43 mg a.i. kg-1 caused 90% feeding inhibition and concentrations above this caused increasing acute mortality to fourth instar larvae. Residues from field pea crops sprayed at 40 g a.i. fell to 0.43 mg a.i. kg-1 2-3 weeks after application. Two to 3 weeks protection is probably the maximum time for residual activity to be useful because the crop outgrows the sprayed foliage. To ensure that larvae are exposed to the maximum area of treated surface, the spray should be timed to coincide with the appearance of larvae in the crop, rather than spraying at a particular growth stage of the crop.