For example, an oil with 21 carbon atoms per molecule is less likely to be phytotoxic than an oil with 25 carbon atoms per molecule. The situation is complicated by the fact that all oils have a range of molecules with different numbers of carbon atoms. As the range of molecules with different numbers of carbon atoms is reduced, there is less chance that the oil will contain a number of molecules of sufficient size to damage the plant. Do not spray on days when maximum shade temperature is likely to exceed 35 o C. Do not spray when soil is dry. Ensure that the oil-water mixture in the spray tank is well agitated to prevent separation.
Argentine ants cause an increase in scale numbers on fruit trees.
The ants feed on the honeydew secreted by the scale insects. This feeding disturbs the tiny wasps that lay their eggs inside the scale and the level of parasitism is considerably reduced. Argentine ants are present at Harvey and they may be one reason why Chinese wax scale is such a problem there. A butt treatment with an insecticide such as Lorsban , good weed control and skirt pruning to prevent any other access to the tree may be necessary to prevent the ants infesting the trees and interfering with biological control agents. Acknowledgements Photographs were provided by Kevin Richards and Bill Woods.