The effect of insecticide treatment on the yield and botanical composition of sown pastures in Western Australia

Abstract

The yield and botanical composition of established, sown pastures were measured after applying insecticides to control the red-legged earth mite. Halotydeus destructor (Tuck.), the lucerne Flea, Sminthurus viridis (L.) and the webworm, Talis spp. The response to treatment depended upon the pest involved, the numbers present, and the vigour of the pasture. Control of H. destructor resulted in an average response of 3.9. cwt an acre of extra dry matter in the spring. To consume this, it is sugested that stocking rate should be increased by about 1/4 sheep per acre. This could be raised to 1/3 sheep per acre by careful selection of treatment areas. Slightly greater responses, up to perhaps 1/4 sheep per acre, can be expected when S. viridis is plentiful. Heavy webworm attack reduced carping capacity on average about one sheep per acre. The economics of insecticide treatment are examined in the light of these results. A formula is given whereby the farmer can calculate the likely return from treatment on his own property. It is concluded that in a large number of cases treatment is near the borderline of profitability. Farmers should make certain that insecticide treatment is the best way of spending their money. Having decided to use insecticides they should (a) treat only those areas where obvious damage is being done and avoid any blanket spraying programme and (b) ensure that some positive use is made of the increased herbage following treatment.