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How to dash drift

Drift has always lurked as a potential threat to applicators as they put pesticides on crops. It will increase, though, due to these factors.

  • Less use of glyphosate-only applications on glyphosate-tolerant crops. Glyphosate is a systemic herbicide. Although glyphosate can drift, applying it in larger droplets can help curb its drift potential while still giving satisfactory control. Currently, 13 glyphosate-resistant weeds have surfaced in 31 states. This will lead to the use of alternative chemistry, some of which may have more drift potential.
  • New people in your neighborhood. Former city residents now residing on country acreages likely won't tolerate tomatoes in their gardens getting dinged by off-target pesticides.
  • New crops and farmers. You may farm next to organic farmers, whose livelihood depends on being able to prove their products are pesticide-free.

“There is an ever-increasing and ever-important vineyard culture (in the Midwest),” says Mike Owen, Iowa State University (ISU) Extension weed specialist. “When you go east, the vegetable culture is increasing.”

Growth regulator herbicides like dicamba (active ingredient in Banvel and Clarity) and 2,4-D are particularly damaging to grapes at fractions of labeled application rates. For example, current 2,4-D formulations can damage grapes at 100 times lower than labeled rates, according to Purdue University data.

“When you fight marestail with 2,4-D, it can be a real issue if you have lots of vineyards in the area,” says Chuck McDonald, seed and chemical specialist for Wabash Valley Service Company in Oblong, Illinois.

“Today, we have few drift complaints due to Roundup Ready,” says Jim Reiss, vice president of agricultural chemistries business for Precision Laboratories. “This will increase when more chemicals are mixed. We have been lulled to sleep in the way we spray.”

Following are four recommendations to minimize drift.

1. Know Droplet Size

Bear in mind that fine droplets are more prone to drift than more coarse droplets. Chris Boerboom, formerly a University of Wisconsin Extension weed specialist who's now a North Dakota State University administrator, points to research comparing the travel path of a fine 100-micron droplet to a coarse 400-micron droplet.

“The fine droplet took 10 seconds to settle 10 feet; the coarse droplet took two seconds,” says Boerboom. “When wind was applied to the droplets, the fine droplet moved 44 feet to the side. The coarse one moved only 9 feet.”

Today's herbicide labels are specifying the droplet size to use. For example, Liberty's label says to use nozzles that create medium-size droplets between 300 and 400 microns.

2. Watch the Wind

Keep the following factors in mind when spraying regarding wind.

  • Know where sensitive areas are, such as vineyards, says Bob Wolf, retired Kansas State University Extension application specialist who now operates Wolf Consulting & Research, LLC.
  • Do not spray at any wind speed if the wind is blowing toward these areas. Spray only when prevailing winds blow in a safe direction between 3 mph and 10 mph.
  • Don't spray during dead calm conditions. This is fertile ground for drift via temperature inversions to occur.
  • Beware of light winds between 0 mph and 3 mph. They can be unpredictable and can quickly change.

3. Be Wary of no Wind and Hot Days

That's because off-target pesticide movement can occur even when no wind exists via temperature inversions. Wolf makes these two points regarding inversions.

Normally, air tends to rise and mix with the air above. The smaller pesticide droplets that do not penetrate the targeted areas rise with this air. Usually, they disperse with little problem.

Not so with a temperature inversion. Increasing temperatures above the crop canopy prevent bottom air from mixing with upper air. Small, suspended droplets with unpredictable movement then form. The cloud could land in an area with little effect, or it could hit a vineyard with $4,000 to $5,000 per acre in crop value.

Clear to partly cloudy skies with light wind at sunset set the stage for inversions. Inversions typically last into the morning, until the sun begins to heat the ground and the wind picks up. Wind direction is often unpredictable.

That's why Wolf advises to be careful spraying near sunset or early in the morning until an hour before sunrise unless:

  • There is a low, heavy cloud cover.
  • Wind speeds are greater than 5 mph to 6 mph on the ground.
  • Temperatures rise 5°F. or more after sunrise.

One way to identify an inversion is by smoke bomb or smoke generator. If a cloud forms and hangs, avoid spraying, says Wolf.

4. Clean your Sprayer Tank and Booms

That's because there's more switching between chemicals in sprayer tanks than has occurred in recent years.

“Switching from one herbicide to another can increase the risk of cross-contamination,” says McDonald.

This will particularly take on new concern when dicamba-tolerant soybeans premiere later this decade, says Owen. Glyphosate used after dicamba without proper sprayer cleaning can cause soybeans not tolerant to dicamba to be damaged. That's because glyphosate – which initially used as an industrial cleaner – can scrape off touches of dicamba and apply them to fields.

Boerboom notes a demonstration he did in Wisconsin in which he tested for dicamba residues lingering in spray tanks. Following a dicamba application, a field sprayer was drained, washed, and flushed with an ammonia water solution and then filled with water. Dicamba still remained in the spray tank and spray boom. Spray-boom dicamba residues were 945 parts per billion (ppb), or.02% of the use rate. Damage can occur with.01% of use rate with dicamba. Concentrations were even higher in the spray boom, with 24,800 ppb (.63%) of use rate.

“The .63% rate is a pretty good dose of dicamba,” says Boerboom. “I guarantee you would injure soybeans if they were sprayed with the next load.”

That makes thorough cleaning a must. “Use the tank cleaner recommended on the herbicide label,” he says. “Also, try to spray your tank empty at the end of the day. If there are any residues stuck in the tank, they may dissolve back into the spray mix while standing overnight.”

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