Posted: July 14, 2006
The AgTech Centre studied the effect of water rates to find answers
Growers have questioned water rates for many years considering some sprayers and aerial applications have been using less than 56 L/ha (5 gpa). Industry generally believes high water rates provide the proper coverage and penetration needed for most applications. "But farmers would like to use lower water rates for economic and practical reasons," says Brian Storozynsky, sprayer technology specialist with the AgTech Centre in Lethbridge.
Current water rates used by growers in Southern Alberta to apply foliar fungicide, for example, range from 10 to 20 gpa (112 to 224 L/ha) and to apply herbicides, rates range from 5 to 10 gpa (56 to 112 L/ha). In some desiccation applications rates up to 40 gpa (448 L/ha) are recommended. High water rates certainly reduce spray drift and provide extra coverage.
Overall, water application rates of 10, 20 and 30 gpa (112, 224 and 336 L/ha) in the 2005 fungicide study in dry beans did not significantly affect disease incidence. This trend was similar to studies done between 1999 and 2001, with other foliar fungicides on dry beans using water rates of 5 and 15 gpa (56 and 170 L/ha).
Over four years, water rates of 5 and 20 gpa (56 and 224 L/ha) used to desiccate potato crops prior to harvesting were studied. Again, no significant difference resulted from using less water as both treatments still resulted in requiring a second application to completely desiccate the potato vines.
Five years of testing using herbicides in field peas showed similar results in water rates. At recommended chemical rates, results were similar for 10 gpa (112 L/ha) and 5 gpa (56 L/ha) with all nozzle types. Only one year of a five-year study using a contact herbicide in a canola crop showed applying 5 gpa (56 L/ha) had less weed control than at 10 gpa (112 L/ha). "This may be attributed to moisture conditions and weed populations being abnormally high that spring," says Storozynsky. All nozzles used in these studies were operated at manufacturers recommendations.
In extreme growing conditions such as advanced weed stage and high weed populations, plots sprayed at 10 gpa (112 L/ha) showed weed control was usually more consistent than at 5 gpa (56 L/ha). "This is an indication that things can go wrong if recommended water and chemical rates are not adhered to with some chemical types," says Storozynsky.
Most spraying technologies performed similar at low and high water rates when appropriate nozzles were selected and used as recommended. Herbicide efficacy depended more on herbicide rate, weed growth stage, population and growing conditions rather than water rates. "The take-home message is to follow the manufacturer recommendations for the nozzle you are using," says Storozynsky.
During extremely wet growing conditions or heavy weed populations, using recommended chemical rates, spraying at early stages and using higher nozzle pressures improved efficacy, especially for venturi-type nozzles.
In terms of the sprayer type used, air assist systems showed more potential in fungicide applications, while electrostatic sprayers were more effective in pre-burn applications.
More information on the spray technology research at the AgTech Centre can be found in the June 2006 edition of the Innovator newsletter.
Reprintable with credit. Available for reprint, with acknowledgement of Canada Sprayer Guide.
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