Importance of the timing of chlorfenvinphos and fenitrothion sprays for the control of corbie and winter corbie in Tasmania

Abstract

Two field trials, one each on the insecticidal control of corbie (Oncopera intricata Walker) and winter corbie (O. rufobrunnea Tindale) were conducted in Tasmania in 1968 and 1969 respectively and the results are presented and discussed. In both trials chlorfenvinphos at 46, 69 and 92 g active ingredient (a.i.) ha-' and fenitrothion at 131 164, and 196 g a.i. ha-1 were applied at three times. All treatments significantly reduced larval numbers. The effectiveness of the sprays was not directly influenced by the incident of rain or temperature. In both trials the later sprays reduced numbers more than earlier sprays. However, it was notable that there was considerable natural mortality in the untreated plots during the experiments. It is concluded that chlorfenvinphos and fenitrothion are suitable replacements for DDT in the control of corbie and winter corbie. However, when chlorfenvinphos is used against heavy populations of small larvae the rate of application should be higher than that used later in the season against larger larvae and care should be taken to ensure that the pasture is short at the time of spraying.