Improving spray distribution and coverage on avocado trees in low volume, concentrate sprays

Abstract

Avocado trees in New Zealand orchards are planted on squares spaced 7-14 m apart with tree heights of up to 14 m. Large trees present considerable difficulties with regards to pesticide application. A series of studies was undertaken on 6-8 m high trees to optimise formulation prescriptions for airblast application of copper sprays. Treatments included standard (up to 3000 litres/ha) and low volume (600-1000 litres/ha), concentrate spray applications applied with the addition of varying rates of an organosilicone superspreader adjuvant. Spray deposits were measured on foliage in the inner and outer sections of the lower, mid and upper tree canopies. Low volume concentrated sprays with the superspreader adjuvant added gave higher and more evenly distributed spray deposits on positions throughout the canopy than standard sprays. Three times concentrate sprays were more effective than five times concentrate sprays because of the large canopy volume of the trees. The adjuvant maximised coverage and evenness of spray deposits.