FEATURE ARTICLES
Wild oat herbicide rates, water volumes & nozzles
Chemical response to different water volumes and spray quality
Posted: April 16, 2006
There is increasing interest in improving the efficiency of a spray operation by reducing water volumes. At the same time, many applicators are switching to low-drift nozzles to reduce drift or to extend the time available for spraying. Applicators need to know if and when they can expect a loss of performance with coarser sprays and lower carrier volumes.
Dr. Tom Wolf, from Agriculture and Agri-Food Canada, explored this idea in a recent research project. The interactive effects of water volume and spray quality on the efficacy of selected wild-oat herbicides on tame oats were studied in a three-year test. Sprays were applied in three spray qualities (Medium, Coarse, and Very Coarse), and each of these spray qualities was applied using water volumes of 45, 85, and 125 L/ha (4, 8 and 11 gpa). Results showed that individual herbicides differed in their response to these variables.
Of the Group 1 products, Horizon was the most tolerant, with good weed control at the Medium and Coarse spray qualities at all three water volumes. Weed control was reduced at the lowest water volume when the Very Coarse spray was used.
Assure was the most sensitive Group 1 product, showing reduced control with Very Coarse sprays at all water volumes, and acceptable control for Coarse sprays only at 85 L/ha (8 gpa) or greater.
Puma was intermediate in its response, with acceptable control using Medium and Coarse spray qualities (but not coarser) at all water volumes.
Everest, a Group 2 product, did not show any sensitivity to water volume or spray quality, likely due to post-spray rainfall that provided additional soil activity.
For Group 1 products, Wolf recommends that low-drift sprays should be applied in no less than 85 L/ha (8 gpa) and that Very Coarse sprays should be avoided. Group 2 products with soil activity do not need this restriction if rain is expected.
More information can be found in the complete research report (PDF).
See related article "Four Rules of Nozzle Selection."
