Spray Drift: Checking Wind Speed Isn’t Enough – DTN

    Licking your finger and holding it above your head won’t cut it anymore when it comes to checking wind speed before spraying this spring.

    The stakes for avoiding spray drift are higher than ever, with new herbicides and herbicide-tolerant crops trickling onto the market and acres of sensitive crops such as grapes on the rise in many agricultural states, experts told DTN. Yet many applicators and farmers continue to rely on their instincts when it comes to assessing wind speeds before spraying.

    “I work with pesticide application all the time, and even I’m not good at estimating what the wind speed is,” said Scott Bretthauer, a University of Illinois Extension specialist, who works with the university’s Pesticide Safety Education Program.

    Applicators and farmers put themselves and their businesses at risk every time they spray a field without documenting the wind speed, added Bob Beck, an agronomist with Winfield Solutions.

    “I would guess people underestimate the wind speed most of the time,” he told DTN. “There is a lot more litigation these days, so not protecting yourself is kind of foolish.”


    Springtime, when spraying picks up and crops start growing, can be an especially dangerous time to brush aside wind speeds, according to a University of Missouri study.

    MU senior research specialist Mandy Bish analyzed hourly wind speeds at five locations around Missouri from the months of March through August for the past 15 years. In the months of March, April, and May, between the hours of 9 a.m. and 3 p.m., she found that hourly wind speeds consistently rose above 9 mph — the maximum wind speed threshold set by the EPA for spray safety. Currently, most herbicide labels list safe wind speeds for spraying between 3 mph and 10 to 15 mph.

    The windy months of March, April, and early May coincide with most pre-plant and burndown herbicide applications, Bish pointed out.

    “Our concern with pre-emergent herbicide applications in those earlier months is that it can be tempting to ignore wind speed (and direction), because there are no or very few row crops that have emerged or are growing when the burndown or pre-plant herbicide is being applied,” Bish told DTN. “However crops such as grapes and other perennial plants can be especially sensitive to herbicides as the plants come out of dormancy during those spring months.”

    While Bish’s data were limited to Missouri, it’s not a stretch to believe that other Midwestern states face similar wind trends, said Missouri State Climatologist Pat Guinan. “In general, what you’ll find if you look at hourly wind speed climatologies for other states in the Midwest, is that winds typically peak during the late morning through the afternoon hours,” he told DTN in an email.


    New herbicide-tolerant crops and their corresponding herbicides are slowly making their way to market, namely Xtend (Monsanto’s premix of glyphosate and dicamba), Enlist Duo (Dow AgroScience’s formulation of 2,4-D choline and glyphosate), and Syngenta and Bayer Crop Science’s HPPD-resistant soybeans.

    The arrival of these new herbicides comes on the heels of another trend: a steady rise in grape acres in the U.S. over the past two decades, a crop notoriously sensitive to herbicide injury, Beck noted.

    The IRS estimates that between 1999 and 2007, the number of vineyards in the U.S. more than doubled to 5,400. Since 2007, the number of grape acres tracked by the USDA’s National Ag Statistics Service has risen 12% to more than 1 million acres in 2014. Moreover, that growth has not been limited to the traditional wine country of California, the IRS noted in a wine industry audit, calling the rise of vineyards in the other 49 states “dramatic.”

    With these trends in mind, Beck and Bretthauer strongly recommend that growers invest in handheld wind speed meters. The investment is small, Beck noted. Most handheld anemometers fall between $90 and $150, with the higher-end ones supplying other relevant information, such as wind direction, temperature and relative humidity.

    Beck said applicators and growers should take wind speed and wind direction measurements when they enter a field to spray and as they are leaving.

    Be sure to take the measurements at the height of your spray boom, Bretthauer added. “What a lot of guys will do is hold that wind meter up in the air or they’ll stick it out of the cab, and that’s not where their nozzles are at,” he noted. “You want to do a fair assessment of where you’re going to be spraying, not 5 feet in the air. It surprises people how big a difference there can be — up to 5 mph faster.”

    Log those measurements and keep the records safe and available, Beck said.

    “If you ever face any litigation, they will go to nearest airport and get wind speed there,” if no other record exists, Beck pointed out. “Airfields are typically flat, so the wind speeds are higher there and they’re taken at heights much greater than the boom height of your sprayer.” It’s not unusual to find that the wind speed 20 inches above your crop canopy is 2 to 3 mph slower than a nearby airport’s reading, he said.


    The Latest

    Send press releases to Ernst@Agfax.com.

    View All Events

    Send press releases to Ernst@Agfax.com.

    View All Events