Phenology of hazelnut big bud mites in Canterbury and implications for management

Abstract

Eriophyoid big bud mites are key pests of hazelnuts throughout the world, although little is known of the identity and impact of the species on New Zealand hazelnut crops. The key objectives of this study were to determine the species of mite present on New Zealand crops, explore a method of monitoring mite emergence from overwintering big buds, determine the phenology of mites in relation to tree phenology and weather, and identify the optimum timing for control measures. The presence of both Phytoptus avellanae (Nalepa 1889) (Acari: Phytoptidae) and Cecidophyopsis vermiformis (Nalepa 1889) (Acari: Eriophyidae) was confirmed, the latter species being a new record for New Zealand. Preliminary diagnostic DNA sequences were determined for both species. A sticky band technique was developed to monitor mite emergence from overwintering big buds, and mite emergence was found to occur between early and late spring. Mite emergence and movement occurred when daily temperatures were greater than 15 degrees C and when mean temperatures were greater than 9 degrees C, with mite emergence increasing with temperature. It proved difficult to relate the phenology of hazelnut to mite emergence, however, the development of new buds during mite emergence was a crucial factor in the infestation of new buds. An accumulated heat sum model (DD), started at Julian date 152 and using a lower threshold temperature of 6 degrees C, predicted the onset of emergence on two cultivars and at two sites as occurring at approximately 172 DD. A regression model based on leaf number, bud height, bud width, DD and Julian date provided a more satisfactory prediction of percent accumulated mite emergence. It is recommended both peak mite emergence and the appearance of hazelnut buds should be used to optimise the time to apply control measures. Therefore, a control should be applied before buds measure 0.5 x 0.5 mm (width x height), are enclosed within the axil, and have a rounded tip, or, when 50% accumulated mite emergence has occurred, which ever occurs first. A preliminary field experiment tested the application of sulphur (40 g/10 litres of 800 g/kg No Fungus Super Sulphur) at 2, 50 and 80% accumulated mite emergence. The greatest reduction in mite numbers was achieved with an application at approximately 50% emergence. Considerable variation in mite emergence occurred between years, therefore optimum timing of controls would need to be determined by monitoring mites, new buds and weather conditions each year. Field collection of mites also identified the presence of Typhlodromus doreenae Schicha (Acari: Phytoseiidae) which would warrant further study for inclusion in an integrated mite control programme.