Efficacy of reduced volume and reduced dose rate spray programmes in apple orchards

Abstract

Four large-scale randomized block experiments in commercial apple orchards (cv. Cox) in Kent, Southern England, compared the efficacy of very-low-volume (VLV) spraying using Micron X1 spinning-disc nozzles at a volume rate of 50 l ha −1 with low-volume (LV) spraying using small-orifice hollow-cone hydraulic nozzles at a volume rate of 100 l ha −1 and conventional medium-volume (MV) spraying using standard hydraulic nozzles at a volume rate of 440–500 l ha −1. A range of fungicides, insecticides and plant growth regulators and nutrients was used in a full season's spray programme in each experiment, the full and one-quarter of the manufacturer's recommended dose rate being investigated. Conventional MV spraying with full manufacturer's dose rates was the most liability effective merthod of applying the full range of crop protection chemicals, but VLV and LV spraying at the full dose rate were often as effective, or nearly as effective, and satisfactory for commercial purposes. Exceptions were control of blossoms wilt ( Sclerotinia laxa f. sp mali) with sprays of vinclozolin, and extension growth cotrol with the plant growht regulator paclobutrazol where VLV spraying was significantly less effective than MV spraying. Reducing dose rate by 75% resulted in a significant, though small, reduction in efficacym and greatly reduced dose rates of calcium chloride application resulting from VLV (approximately one-tenth dose rate) and LV (approximately one-fifth dose rate) spraying at the same concentration as MV spraying were identified in raising the concentration of calcium in the fruits. Commercial success with greatly reduced dose and volume rates will require careful orchard monitoring for pests and diseases, coupled with a flexible management strategy of adjust choice of pesticide, frequency of application and dose and volume rate suit prevailing conditions.