NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665
May 4, 2000
In crop spraying, it's the end result -- dead weeds, reduced disease and healthier crops -- that count, reminds a North Dakota State University agricultural engineer.
"We've done a considerable amount of research on ground and aerial application equipment by measuring the area of spray coverage of leaf surfaces," says Vern Hofman of the NDSU Extension Service. "Some people may have misinterpreted this to mean that higher coverage translates into higher yields. That's not correct, and producers should be aware that the study did not contain any method of measuring pesticide performance or the effect on yield."
The NDSU research to measure the coverage on plant surfaces was done by using a fluorescent dye mixed with water that was applied to potato and sugarbeet leaves and wheat heads. After spraying, leaves or grain heads were collected from plants and exposed to an ultra-violet light that caused the dye to glow. A low light camera captured an image for analysis by computer which calculated the percentage of leaf area covered with spray.
"One of the key issues for producers is that the research only measured differences in initial coverage, not product performance," Hofman says. "The trials only measured the area of coverage on the leaves, not the amount of active ingredient."
Why is that distinction important? Consider the concentration of the spray for example, Hofman says. When comparing droplets of equal size, a 5 gallon per acre (GPA) droplet will contain four times more active ingredient than a droplet produced at 20 GPA. The 20 GPA application must therefore place four times more droplets on each leaf to deposit the same amount of active ingredient as a 5 GPA application. The trials did not find that 20 GPA consistently provided four times the amount of coverage as 5 GPA. "Delivery of the active ingredient is vital to maximize performance," he says.
"Timing of a pesticide application also is extremely important," Hofman says. Maximum economic performance is achieved with the proper timing of an application. Delaying a pesticide application for too long may reduce performance and may not generate an economic return. "Irrespective of the type of equipment used, the application needs to be done during the most effective time period."
To compare performance between application equipment, replicated yield trial results may be best. In 1999, NDSU researchers applied Folicur to a field by aircraft, by conventional ground equipment and with a modified front and back nozzle arrangement. While there were measurable differences in initial coverage, no significant difference was found in harvested yields.
"One year's trial does not constitute conclusive evidence," Hofman says. NDSU has committed to additional trials this year to compare the performance of various types of application equipment as measured by harvested yields.
"Until the research is complete, growers need make decisions based on proven techniques and their own experience," Hofman says. "Producers need to make sure their applicator is competent and is using equipment that produces a good spray pattern. If equipment is in good condition, calibrated and operated properly, both ground and aerial application can be accomplished with good success."
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Source: Vern Hofman (701) 231-7240
Editor: Tom Jirik (701) 231-9629