Drift damage from off-target applications of low-rate glyphosate might not cause significant damage early in the season, but the same can’t be said of dicamba and 2,4-D.
Some of the newer herbicides that make glyphosate hotter can have lasting effects for non-compatible crops.
Not only is herbicide drift a potential liability, but it also wastes spray by reducing the efficacy of the original application.
Researchers say there are two forms of drift: vapour and particle.
Vapour drift occurs when spray reaches its intended target plants but then moves on to where it isn’t wanted.
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This can happen during thermal inversions or when there is rapid change in temperatures and light winds. It can also occur early in the season.
Chemistries that are prone to volatilization are generally marked on the labels.
Bill Johnson of Purdue University in Illinois said there is little producers can do to avoid the problem other than using less volatile formulations and avoiding spraying on days when conditions are likely to cause trouble.
Particle drift is the most common type of drift and is often caused by excessive wind speeds.
Bob Wolf, who operates Wolf Consulting and Research in Mahomet, Illinois, said using technology to reduce drift is more complicated than just choosing the right nozzle.
“This isn’t new. We’ve been talking about big and little droplets for many years. Big droplets might miss their target, small droplets might never get there. It’s all about getting to a happy middle.”
All nozzles create several sizes of droplets, depending on pressure, but getting the greatest uniformity of droplet and spray pattern is what improves application efficiency.
Extended range flat-fan nozzles have been around for 30 years. They were the first drift reduction nozzles and provide a tapered edge pattern with 50 to 60 percent overlap at 15 to 60 pounds p.s.i. of pressure.
Wolf said they work best 18 to 20 inches high on an 80 degree fan.
Application should always be above 10 gallons per minute.
Turbo flat fans such as those from TeeJet reduces pressure inside the unit, which creates bigger droplets.
The design has a wide operating pressure range of 15 to 90 p.s.i. It keeps the flat fan tapered pattern edge and a 50 to 60 percent overlap.
Venturi air induction nozzles are popular because they provide a medium to large size droplet and still give good overall coverage. They include Greenleaf AirMix, Teejet’s XR with an air aspirator and the Hypro Guardian Air Induction.
These nozzles bring in air to produce a large droplet and offer good coverage with reasonable drift control between 50 to 80 p.s.i.
Flat fans offer reasonable drift protection between 20 and 25 p.s.i.
Chamber type nozzles, including the Wilger design, are best between 30 and 40 p.s.i.
Early venturi types are most effective from 35 to 45 p.s.i.
Air induction units are the most recent technology. Wolf said they are combined with turbulation chambers to create the largest droplets over the largest range of flows and pressures.
However, improved drift reduction can reduce efficacy.
“We can misuse these technologies,” he said.
“Run too high or low a pressure or mis-set boom heights and things start to go wrong.… Droplet sizes vary, stripes start to show up.”
However, bigger isn’t always better with some of the newer products.
Tom Wolf of Agriculture Canada said products such as carfentrazone and saflufenacil are more sensitive to droplet size than glyphosate.
“Good old glyphosate is pretty forgiving about droplet size,” he said. “Some of these other products are not.”
Bob Wolf advised producers to look up the manufacturer’s recommended droplet size and then calculate the gallons per minute based on achieving the recommended droplet and the combination of speed and application rate needed to get over the land.
“You can’t use one nozzle for all your herbicides and get the efficacy you expect and still control drift,” he said.
Five ways to reduce the drift
•Choose a herbicide that can handle large droplets. Glyphosate products that have contact-actives in the mix, such as CleanStart or Heat, are less likely to perform well with big droplets than those that contain Group 2 and 4 mixes
•Use a low-drift nozzle and operate it so it produces a coarse to very coarse spray quality, as described by the manufacturer. Low-pressure air-induced nozzles such as Air Bubble Jet, Greenleaf AirMix, Greenleaf TurboDrop XL, TeeJet AIXR, Hypro Guardian Air and Hypro ULD operated at 50 to 60 p.s.i. will be very low drift, as are pre-orifice nozzles such as Wilger SR, MR and DR. Keep the spray finer and the pressure higher if using contact modes of action
•Keep the boom low. The minimum 100 percent overlap is all that is needed, which is for the edge of one nozzle pattern to spray into the centre of the adjacent pattern
For most nozzles, that is a boom height of close to 20 inches. An automatic boom levelling system is useful
•Know what’s downwind. Try to avoid fields that have sensitive areas downwind such as water, shelterbelts, pastures and people. Check the buffer zone restrictions on the label. They also provide an idea of whether the product is harmful in water or on land, or both
•Let the weather help. Take the wind from the side if possible. Going straight into the wind creates a lot of extra drift. Spray when the sun shines. Drift moves further distances in early morning and late evening and on cloudy days. The drift cloud disperses quickly and causes less damage when it’s sunny
•Talk to affected people first if you feel that drift is unavoidable and that someone might be affected
Sources: Tom Wolf, Agriculture Canada; Steve Larocque, Beyond Agronomy
