Effectiveness of spring spraying targeting diapause egg production for controlling redlegged earth mites and other pests in pasture

Abstract

Earth mites are a complex of related species introduced into Australia in the early part of last century that cause economic damage to crops, especially canola, and to pastures. A general method of chemical control aimed at interrupting the life cycle at the most effective stage, by spraying in the spring before the mites enter diapause, has recently been adopted for controlling earth mites, particularly the redlegged earth mite Halotydeus destructor (Tucker). Here we use paired-paddock treatments and field enclosures to test the effectiveness of this method on pest populations of H. destructor as well as on other pests over two seasons at multiple pasture sites in Victoria. Halotydeus destructor numbers at the start of the winter growing season were suppressed by up to 85%, but this control level was not sustained. The numbers of H. destructor and other pests were similar to or higher than those in the unsprayed areas by spring. Spring spraying is, therefore, a useful means of suppressing H. destructor in early autumn, but its effects disappear relatively quickly over time in Victoria. This strategy also has little impact on the control of the blue oat mite Penthaleus major (Duges) and other phytophagous invertebrate pests.