5 December 1997

Try a switch to spray-on types

GRAIN store pest control could be much improved by switching from dust to spray-on formulations, according to early results from MAFF-funded research.

"Results achieved so far indicate pesticide efficacy can be enhanced by formulation choice," says Debbie Collins, stored product entomologist at CSL.

"In some cases shorter chemical exposure of a particular formulation results in longer periods of insect protection and reduced residue levels."

Four different formulations are currently under review: Microencapsulated (mc), emulsifiable concentrate (ec), ultra low volume (ulv) and dust.

Best product

"The mc suspension has so far proven to be the most effective formulation against saw-toothed grain beetle, grain weevil and rust red flour beetle," explains Miss Collins. "After seven days of exposure to doses of 2mg/kg, complete insect mortality is achieved for 36 weeks, with residue levels of just 0.7mg/kg remaining at the end of the period.

"Slightly lower levels of control are achieved using the same rate of ec, but higher residues suggest the formulation is less effective.

"ULV and dust formulations provide just 20 weeks of insect mortality at 2mg/kg, and require almost twice as much chemical in order to achieve comparative control.

"At the start of the project all four formulations were available commercially," says Ms Collins. However, mc and ulv formulations have both now been withdrawn. Of the remaining formulations available, ec is considerably more effective than dust, she says.

&#8226 A spokesman for Actellic (pirimiphos-methyl) manufacturer Zeneca says the difference in performance between formulations was not sufficient to maintain the availability of an mc formulation.