Integrated control of apple pests in New Zealand 9. Development of European red mite populations under minimal control strategies

Abstract

Development of European red mite (Panonychus ulmi) populations was studied from 1975 to 1977 in an orchard released from regular application of acaricides and supporting insignificant numbers of natural enemies of the mite. Populations grew rapidly from mid January, and reached higher levels on Hawke’s Bay Red Delicious than on Cox’s Orange Pippin or Granny Smith. Extensive early defoliation occurred in all cultivars in response to heavy feeding pressure. Application of cyhexatin in February 1976 failed to control populations in Granny Smith and Cox’s Orange Pippin, and only temporarily suppressed populations in Hawke’s Bay Red Delicious. Removal of all acaricide applications in 1976–77 on Hawke’s Bay Red Delicious showed that high population levels (365 mites per leaf) could develop. Stratification of sampling in Granny Smith showed that population densities decreased from the tree centre, through outer fruiting clusters, to current season’s shoots. Winter egg deposition on apples was studied in relation to various P. ulmi densities. Early harvest of Cox’s Orange Pippin prevented large numbers of winter eggs being laid on the fruits in spite of high P. ulmi densities; late harvest of Granny Smith exposed fruit to greater winter egg deposition. The intermediate harvest date of Hawke’s Bay Red Delicious resulted in fewer winter eggs on apples than for Granny Smith, in spite of much higher P. ulmi densities. On Hawke’s Bay Red Delicious, oviposition preference was for calyces of fruits not exposed to direct sunlight. A relationship between maximum P. ulmi densities and numbers of winter eggs on fruits is demonstrated.