Promise in new pyrethroids for one-shot grass grub control

Press, 10 December 1982, Page 22

Promise in new pyrethroids for one-shot grass grub control

A new range of pyrethroids becoming available in New Zealand could be an effective means of grass grub control. Research of Ruakura Soil and Plant Research Station on control of the pasture pets has recently concentrated on single spray applications of long-lasting pyrethroid formulations. Two Raukura scientists Drs Denis Lauren and Ron Henzell, have studied grass grub eradication over the last eight years. They now feel they know the requirements for chemical control and are looking for an economically effective formulation.

Dr Lauren said multiple applications of Cypermethrin emulsfiable concentrate (E.C.) provide effective control. Three sprays are given at six day intervals based on a predicted “ideal treatment date” calculated from estimated mating dates. “Unfortunately there are practical problems with this multiple spray treatment,” he said. “For best control the second and third applications must be at exact time intervals. Wind or rain could easily disrupt the schedule.” To overcome this problem the scientists have examined longer-lasting pyrethroids. Best results have come from Deltamethrinwettable

powder (W.P.). Trials have shown that a single application of this gives similar control levels to those obtained from three applications of Cypermethrin EC. “At an application rate of 100 grams a ha, Deltamethrin WP gave a grass grub population reduction of 81 to 84 per cent. This was as good as the 82 per cent control from three application at IOOg a ha of Cypermethrin EC,” Dr Lauren said. The emulsifiable concentrate of Deltamethrin gave controls of 67 and 78 per cent on two separate trials one week apart. Dr Lauren said emulsifiable concentrates tended to lose activity after

six to seven days as they were absorbed into the plant. “Were not sure why the wettable powder works so well in the field. It certainly seems to last longer on the soil and can kill the grubs before they get onto the grass,” he said. Dr Lauren said the work at Ruakura on available synthetic pyrethroids was “just the tip of the iceberg.” “Use of Deltamethrin itself probably won’t be possible,” he said. “We have found out that it is not going to be commercialised and applications at the rate we’ve been using would make it uneconomic.” The good news, however, is that many other synthetic pyrethroids are becoming available. Dr Lauren said any promising new ones which met the established control requirements would be tested. "We are now at the practical stage of research where we are looking for an economic pyrethroid which is effective as a single spray treatment.” There is already one type of pyrethroid available in Australia which may hold promise. Applications of 100 g a ha Deliamethrin WP would cost about $lBO a ha. The Australian pyrethroid applied at the same rate would cost $6O a ha.