Sprayer Clean-outs – Extra Vigilance Required to Remove Some Tank Residuals

Often the problem with a sprayer clean-out is that the tank looks clean but isn't. Several tank loads later, detergent action by a surfactant with a different product may release the active ingredient that's been stuck under a layer of oil or on a filter screen. If this chemical hits a sensitive crop you're in trouble.

A few herbicides leave residue in the sprayer. Most are Group 2 herbicides, which include the SU or sulfonylurea active ingredients. However, they can be rinsed out with ammonia or with a specialty cleaner.

Residual Damage

"The real clean-out issue often centers on changing to Group 2 products in the preseed burn-off," says Denise Maurice, Westco's manager for Agronomic Information Extension in Calgary.

"It's really critical that producers do a thorough clean-out job with ammonia as part of the procedure," says Maurice. "If they can, they should leave the sprayer tank full with the cleaning product for an entire evening prior to spraying the next day," she says. "Even parts per billion of a Group 2 can produce significant injury in canola."

Often damage is traced back to residue on the tank walls or in the filters after a preseed burn-off.

Maurice explains: "Residue gets locked into the spray tank. A couple of insecticides may have been sprayed after that and may still be lodged in the nooks and crannies of the sprayer.

"A week or ten days later, the grower goes into herbicide tolerant canola with Liberty™ or Transorb™. The highly effective adjuvant or surfactant in these products does more than its job. It finally releases the Group 2 that's been lodged in the sprayer. The crop damage can be severe."

A common mistake is to forget that some of preseed burn-off products contain more than glyphosate.

"Producers often think, 'It's just glyphosate', so I'll just rinse it out and go right on into the Roundup Ready™ canola. But if they're using Pre-Pass™ or Express Pack™, they have Group 2 in the tank. They've forgotten that."

Expect the Unexpected

Why some chemicals stick is somewhat mysterious, says Tom Wolf, application technology specialist with Agriculture and Agri-Food Canada at Saskatoon. In fact, the jury is still out in the scientific community.

What they do know is that products containing sulfonylurea (SU) comprise about 95 percent of the sprayer clean-out issues, Wolf says. The typical SU product is a broadleaf killer. It's also often applied in a tank mix with a grass killer, and most grass killers are in an oily solution known as an emulsifiable concentrate.

"It's believed that the oil in that formulation acts as a barrier to removal of the SU. You get SU on the tank wall, trapped by a layer of oil. When you rinse the tank with water, the SU stays trapped there."

Wolfe paints this picture of unexpected damage: A farmer uses a post-emergent product containing an SU and cleans the tank. If the plan is to continue in cereal crops, residue isn't much of a worry. In the meantime, a few loads of grass killer, broadleaf killer or insecticide are sprayed. The tank has a lot of product go through it and may have been rinsed once or twice. Then glyphosate is applied in herbicide tolerant canola and the crop gets Group 2 damage.

"The producer wonders where the stuff came from. The answer, usually, is that the material became lodged on the tank wall and nothing took it off until it encountered the surfactant used in the glyphosate or glufosinate," says Wolf.

Watch Your Filters

A modern high clearance or pull-type sprayer can have a large number of filters. Occasionally, an applicator may forget to clean one.

"The dry flowable formulations can accumulate on screens and refuse to flush through with a quick rinse," Wolf warns. "If the filter is finer than a #50 mesh screen, a concentrated sludge of active ingredient and the carrier, a type of clay, can collect."

If material has collected on a screen, it's obvious and usually an earthy, grayish-tan color.

"The typical symptom of point-source contamination is a V-shape. Damage starts at a point and widens as the material moves to the edge of the boom. You could have several V-shapes, one from each filter in the line of a boom," he says.

To be safe, Wolf says, follow the clean out procedures. Use the full water volumes required. Use the recommended strength of ammonia or whatever commercial cleaner is recommended by the pesticide manufacturer's label.

He points out that ammonia will raise pH and increase solubility of the SUs. It cuts through the grease only to release any active ingredient that may be under a layer of oil on a tank wall.

"Some people believe ammonia neutralizes the chemical. It doesn't," Wolf says. "The active ingredient is just as potent in a wash of ammonia as it is in water."

Crop protection starts with reading sprayer labels from farm supply retailers and in crop protection guides.

*All products are trademarks of their respective companies.

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