Woolly apple aphid - chemical control

There are three approaches to chemical control. Since the 1960s, chemical control has been based on the use of organophosphates. These highly toxic products have provided effective control of woolly apple aphid and other pests but they have had the disadvantage of toxicity to many natural enemies. More recently, the carbamate pirimicarb (Pirimor®) has become available. This combines toxicity to woolly apple aphid with safety to many important beneficial species. Pirimor® is not toxic to any other pipfruit pest. In addition, the neonicotinoid, thiacloprid (Calypso^TM ), has been registered for use on pipfruit for the control of several pests, including woolly apple aphid. Green tip spraying to control woolly apple aphid with Pirimor® or organophosphate normally involves a combination with oil. High volume application is very important to ensure good spray coverage. The woolly apple aphid parasite, Aphelinus mali, is so important for control of this pest in IFP and organic production that care should be taken in the choice of pesticides.

IFP aims to eliminate the use of organophosphates in apple orchards and replace these with more selective chemicals, such as insect growth regulators and neonicotinoids. However, Pirimor® and the organophosphate chlorpyrifos are not suitable for postbloom use on fruit destined for the U.S.A. market. All three chemicals are permitted in IFP at present but with a strong preference for the use of the more selective chemicals, Pirimor® and Calypso^TM . Where organophosphate sprays are still required for the control of woolly apple aphid in summer (e.g. emergency use of diazinon based on monitoring), or where Calypso^TM is used, these uses must be efficiently integrated with the control of other pests, such as leafrollers and scale insects. There are no reports of woolly apple aphid in New Zealand developing resistance to insecticides, although this has been reported overseas (e.g. to vamidothion).

Organic production - Woolly apple aphid does not usually require control in an organic orchard because the pest is kept at low levels by natural enemies. If this is not the case, the cause of disruption of biological control needs to be tracked down and changed.