Spray deposition with conventional nozzles, low-drift nozzles, or permanent sprinklers for controlling apple orchard pests
Panneton, B., Philion, V., Chouinard, G. (2015). Spray deposition with conventional nozzles, low-drift nozzles, or permanent sprinklers for controlling apple orchard pests, 58(3), 607-619. http://dx.doi.org/10.13031/trans.58.10916
© 2015 Her Majesty the Queen in Right of Canada as represented by the Minister of Agriculture and Agri-Food Canada. Field experiments were conducted to compare deposition of spray on leaves in a high-density apple orchard for different spray application systems. A permanent sprinkler system was installed for pesticide applications. Sprinklers were installed above the canopy centered on the tree row and compared to a conventional radial sprayer with reduced airflow and fitted with conventional or low-drift nozzles. The ratio of bottom to top of leaf deposit was closer to 1 with the low-drift nozzles, greater than 1 with the conventional nozzles, and close to 0 with the sprinklers. Leaf coverage with the low-drift nozzles was not statistically different from deposits with conventional nozzles in all tree locations on both top and bottom surfaces of the leaves except in the lower part of the trees close to the trunk, where low-drift nozzles produced higher deposits. Overall, the low-drift nozzles produced less variability in deposits among the positions in the trees. On the trees as a whole, sprinklers and low-drift nozzles deposited more spray than conventional nozzles. Contrary to our initial hypothesis, differences in spray application technique efficacy were more important for insect control than for apple scab control but were generally small. Insect control with conventional nozzles proved slightly better than with lowdrift nozzles, which were in turn slightly better than the sprinklers. Apple scab control under severe infection conditions was equivalent in all three systems, which suggests that pesticide coverage with sprinklers, which is close to a rain pattern, effectively reached infection sites despite minimal coverage of the abaxial leaf surfaces. The absence of pesticide residue on the abaxial surfaces of sprinkler-treated leaves may also serve as a refuge for predatory mites. These results show that perfect coverage is not an absolute requirement for good pesticide efficacy, as exemplified by our results on the efficacy of sprinklers for applying pesticides. Pesticide efficacy results from appropriate coverage of the target, with the target defined by pest epidemiology, crop status, and meteorological conditions.
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