March 17, 2010 – Researchers are
transforming weed control with new precision tools and application
techniques that help keep herbicides precisely where they belong. As a
result, farmers are able to optimize the performance of herbicides and
minimize the small amounts that drift off target as they are being applied.
One of the latest breakthroughs involves low-drift nozzles that can
significantly reduce the proportion of very fine (small) spray droplets that
are susceptible to drift.
“These low-drift nozzles are really having a revolutionary impact,” says Dr.
Tom Wolf, a research scientist with Agriculture and Agri-Food Canada and a
member of the Weed Science Society of America (WSSA). “Research shows we can
reduce the spray that drifts away from its target to less than 0.5 percent
of the applied amount. That’s a decrease of more than 80 percent compared to
The secret is a clever design that reduces the internal operating pressure
of the sprayer nozzle and mixes air into the herbicide spray as it is
seen nearly 100 percent adoption among custom applicators in Canada, and up
to 50 percent of the more innovative growers on large farms are using them
as well,” Wolf says. “They have clearly found the devices work well in
Still, there are obstacles to even broader adoption. Not all weeds and all
herbicides respond the same way when changes are made to reduce the number
of very fine spray droplets.
“It can be tough to provide practical recommendations to applicators on
diversified farms,” Wolf says. “But scientists are meeting that challenge
by communicating their research findings to herbicide manufacturers and
applicators alike. We’re finding low-drift sprays can be used successfully
in the majority of situations an applicator is likely to encounter.”
Robert Klein, a WSSA member and crop specialist at Nebraska’s West Central
Research and Extension Center, recommends combining multiple drift control
strategies in order to achieve optimal results. Here are eight proven
techniques he recommends:
Increase spray coarseness. Switching to
low-drift nozzles has a large impact on drift. For traditional nozzles,
lowering pressure can also increase droplet size and reduce drift.
There is a fine line, however, between droplets that are too small
(causing excessive drift) and too large (providing insufficient
coverage). Look to your nozzle manufacturer for guidance on the
recommended pressure. Low-drift nozzles typically require a higher
pressure to operate properly.
Gauge the weather. Environmental factors can
be critical to the control of spray drift. Klein cites wind speed as
one important example. “When wind speed increases, so does the
potential for drift downwind of the sprayer,” he says. Today’s
ultrasonic weather sensors can help. A far cry from yesterday’s
rudimentary weather vanes, sensors measure air temperature, humidity,
dew point, barometric pressure, wind chill, wind direction and wind
speed. The units are extremely compact and can be mounted inside a
sprayer cab. That means the applicator has continuous, up-to-date
weather data and can apply herbicides when they are least likely to
Control the flow. Modulated flow controls
reduce drift by rapidly pulsing each spray nozzle on and off. This
allows pressure and droplet size to remain constant as the sprayer moves
across the field at various speeds.
Rev up the air speed. Air-assisted sprayers
emit a high-velocity, downward air stream that pushes the spray droplets
directly onto the targeted weeds or treatment area. As a result, they
can reduce drift if used properly.
Create a buffer. Untreated zones around
fields can serve as buffers that keep drift away from off-target sites.
Add drift retardants. If you use a
traditional sprayer, special additives can be used to reduce the number
of fine droplets. Make certain, though, that you select an additive
especially designed for the type of nozzle and herbicide you use.
Certain additives can be a minus when used with the wrong nozzle tip.
Hood your sprayer. By mounting hoods around
the nozzles on a sprayer boom, you can create a physical barrier that
reduces spray drift. It’s a simple but effective technique.
Monitor boom height. Extension specialists
recommend keeping booms close to your weed target in order to decrease
the possibility of downwind drift. But be careful to follow the
manufacturer’s instructions so you maintain the uniform spray pattern
and coverage needed to control weeds effectively.