Very little progress has been made in 50 years worth of work with chemical application equipment, Herb Willcutt told growers attending a recent corn short course in Greenwood, Miss.
Willcutt, an agricultural engineer at Mississippi State University in Starkville, Miss., says, “Sprayers were introduced prior to 1960, and to this day there is not a better nozzle than the flat fan tip nozzle. Granted there have been improvements, but we've made very little progress overall.”
Growers should not whole-heartedly buy into the idea that drift-reducing nozzles will make an application safe under adverse conditions, cautions Willcutt. “Yes, they can reduce droplet size in the spray, but I'm not sure they can do all that manufacturers claim. The only real improvements we've made in nozzle tips are to slightly change the shape of fan-tipped nozzle, and to make nozzles that produce a pattern at lower pressures.”
In 2003, 46 drift claims were filed across Mississippi, with 23 complaints involving aerial applicator drift, seven claims of drift from a ground applicator, and 16 complaints for which the source was not identified. The complaints were primarily related to applications of glyphosate.
The good news is that the 2003 number represents about half of the number of drift complaints Mississippi officials received in each of the previous few years, Willcutt says.
Variables contributing to drift from ground applicators include the downwind distance or the distance between the applicator and target crop; nozzle height; wind speed; air temperature; nozzle pressure; and downward droplet speed. Willcutt calls the nozzle flow rate and droplet size “statistically non-significant,” as a contributor to drift from ground application equipment.
The number one cause of drift from ground rigs is the downwind distance from the applicator, he says. The shorter the distance to a susceptible crop the greater the risk of chemical drift.
For example, if a 10-gallon per acre application would be expected to cause a drift deposit of 14.5 ounces per acre when 10 feet beyond the target swath under spray conditions, moving the applicator 110 feet further upwind from the non-target susceptible crop would reduce drift to about 0.05 ounce per acre. That's 290 times as much drift at a distance of 10 feet as compared to 110 feet downwind. This level of drift for some materials may still cause crop injury.
To increase the downwind distance, Willcutt recommends waiting until the wind is blowing away from the non-target crop, or working with your neighbors to plant similar crops in close proximity to property lines.
The “other biggie” in drift, he says, is wind speed. Comparing wind speed at 1 mile per hour with wind speed of 10 miles per hour, the same 10-gallon-per-acre application would be expected to produce a drift deposit of 0.18 ounce per acre, while a 10-mile-per-hour wind would result in 9.29 ounces per acre of drift deposit, or 51 times the amount of drift at one mile per hour.
“When the wind starts getting up, you should know that product is going to get up and go. That should be no surprise to anyone,” Willcutt says.
The average wind speed over a 15-minute interval at noon was nearly 10 miles per hour on those spring days in 2003 when drift resulted in one or more of the 46 complaints, according to data from Mississippi's Beasley Lake weather station.
“If wind speed averaged 10 miles per hour, there likely were gusts well above 10 miles per hour. That means applications are being made when they shouldn't,” says Willcutt. “Pesticides should generally be applied when the wind speed is 3 to 6 miles per hour, and blowing away from sensitive crops.”
To further reduce the potential for drift when applying pesticides by ground, Willcutt suggests staying downwind of sensitive crops and keeping the boom low to the ground. He also suggests slowing down when you are near sensitive areas, crossing drainage furrows and making turns, because large tires on some floater rigs can become fans, moving spray material high into the air immediately behind the applicator. Leaving booms raised after crossing drainage furrows to prevent dragging in crops or the ground greatly increases drift potential, he says.
Choose chemicals, equipment and nozzles carefully, properly maintain your equipment, and calibrate your spray equipment, recommends Willcutt. “Some materials are safer to adjacent crops and may give similar control to other chemicals that are less selective in the targeted crop.”
Growers also should not be lulled into a false sense of security. Hooded and shielded sprayers can magnify drift when the wind is too high, and especially when the wind is parallel to the direction of travel.
Drift control additives reduce the percentage of the fine drops in a spray application, but Willcutt says it will not keep an application from drifting if weather conditions are adverse for the application to be made. “Drift control additives are not miracle products,” he says. “When in doubt about weather and other conditions being safe to make an application, it is better to leave the material in the jug and the sprayer in the shed.”
Continued incidences of drift could result in restrictions or bans being placed on some herbicides including: greater restrictions on when materials may be applied; greater restrictions on methods of application; greater bookkeeping requirements; greater legal impacts; and the loss of label for some pesticides.
When it comes to aerial applications, Willcutt says that small droplet size is the number one cause of drift, followed by drift distance, wind speed and then boom height.
Research studies analyzing the amount of spray reaching a targeted swath as a percentage of the spray applied indicates that below a 4200 micron droplet size, 40 percent or less of an aerial spray is reaching its intended target within the swatch. Other material may be deposited in adjacent swaths, dissipated into the atmosphere, or deposited on non-targeted crops.
That number increases slightly as droplet size increases, according to laboratory studies. In comparison, even with larger droplet sizes, ground applicators reach their intended target with greater than 90 percent of the spray being deposited within the intended swath in greater than 90 percent of cases, Willcutt says.
Minimizing cases of pesticide drift from aerial application means working with your aerial applicator, matching crops and field locations, keeping neighbors in mind and planting similar crops adjacent to property boundaries. It also means choosing pesticides carefully, watching weather conditions, considering application options, and being flexible.
“Don't force aerial applicators into making an application when the applicator knows conditions may cause drift problems. Some food for thought: The Arkansas Plant Board holds the farmer and the applicator equally liable for drift complaints,” Willcutt says. “If you are going out there at winds of 15 miles per hour with a ground rig, you're playing Russian Roulette. I know some of your do it, and those are the ones that are causing the problems for everyone,” he says.
For more information on drift reduction, Willcutt urges growers to attend the Pesticide Application Stewardship Program March 23 in Stoneville, Miss., and March 24 in Clarksdale, Miss.
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