Take this three-question quiz. If you ace it, consider yourself a spraying wizard. Pass or fail, this information could help you minimize spray drift.

Are these statements true or false?

Unless you answered that all three questions are false, you aren’t a wizard. Either way, keep reading!

Spraying and the environment

“Things you can’t control in the environment are one of three key factors which determine spray drift potential,” says Austin Pearson, a climatologist with the Midwestern Regional Climate Center based at Purdue University. “We’re talking about wind, temperature and humidity impacts, and temperature inversions.”

Mother Nature deals the hand related to weather. Deciding whether it’s best to spray, to wait or to adjust is up to the farmer.

Here is a closer look at weather factors, using the opening questions as a guide:

1. Wind speed. The best option is spraying when winds are 3 to 10 miles per hour, Pearson says. Robert Wolf, a Kansas State Extension specialist who’s now retired, determined that if winds are light, they are more unpredictable, particularly related to wind direction. Plus, if it’s dead calm, it could mean there is a temperature inversion, where cool air at ground level meets warmer air instead of cooler air at the next level. Air doesn’t mix, and fine spray particles can move.

Related:Armyworms on the march

Wolf also discovered that even on a normal day, wind speed increases as height above the crop canopy increases. If it is 5 mph at canopy level, expect it to be 7 mph at 6 feet above, 8 mph at 10 feet above and 10 mph at 20 feet above.

Wolf demonstrated that wind direction is critical. Spray when the breeze is gentle, steady and blowing away from sensitive crops.

2. Wind speed and particle size. Your choice of nozzle and wind speed intersect, Pearson explains. For example, 100 micron particles drift several times farther than 600 micron particles, but just how far depends on wind speed.

At 5 mph, 100 micron particles move about 20 feet, 200 micron particles move less than 10 feet, and 600 micron particles move only a couple of feet. Ramp up to 10 mph winds and the smallest particles go nearly 50 feet, while the largest move less than 10 feet. At 15 mph, very fine particles travel over 70 feet. That’s nearly 50 rows into a 15-inch-row soybean field.

Related:Importance of selecting the right soybean seed treatments

3. Temperature inversion. If winds are stronger than 3 mph, a temperature inversion is less likely, Pearson notes. They’re more likely in late evening or early morning under the same conditions that produce mist, dew, fog and frost. If smoke moves parallel to the ground instead of upward, there is likely a temperature inversion.

In his work, Wolf determined that small particles are most susceptible to moving during an inversion. Minimizing small droplet size lowers potential for drift issues if an inversion occurs.