Spray droplet size matters

Adjuvants don’t make big globlets shrink or fine droplets grow, but it does seem that way

Surfactants have been in common use for decades, but the idea of adding a vegetable oil deposition adjuvant to improve droplet size, enhance coverage and reduce drift is still relatively new.

When a deposition adjuvant is doing its job, more of the droplets are of a uniform size and they are closer in size to the middle range. That means there are fewer fines to be blown away and there are fewer big droplets that waste active product.

Numerous such products are on the market, but nearly all are made with some combination of polymer, guargum and agar. They claim to reduce spray drift, and it’s true that they do achieve that, but the trade-off is poor coverage and poor efficacy.

Polymer, guargum and agar reduce drift by creating larger droplets throughout the spray sheet, which produces a new problem.

Spraying with big droplets is like dropping golf balls on the crop. They fall straight through the canopy to the ground and coverage is terrible. As well, big droplets cause the spray pattern to collapse, which reduces overlap and produces strips with no coverage between the nozzles.

Two companies have addressed the issue by using vegetable oil as a main ingredient in their deposition adjuvants.

Loveland Products

Loveland Products has three main deposition adjuvants available to producers in Western Canada, based on what the company calls Leci-Tech technology. This formula uses lecithin, which is derived from soybeans.

Synthetic polymers used in most drift control agents are long chain molecules that can be physically damaged by continued cycling through a circulation pump and rendered useless in controlling droplet size. Lecithin does not break down with continued circulation.

Chemical engineers at Loveland blend lecithin with other ingredients, which serve to bind the fine spray droplets together. The company has a 30-year history of manipulating the lecithin component used in many of its products.

LI700 and Liberate are touted as being deposition aids, drift control agents and non-ionic penetrating surfactants.

Jeff Crampton, the Loveland representative for Western Canada, said LI700 is also an acidifier.

“Liberate is a 100 percent non-ionic surfactant. LI700 is similar, only it’s 80 percent non-ionic,” said Crampton, who added that Valid is a utility modifier, marketed only as a drift control agent.

“LI700 will reduce the pH of the water, which is required in certain products such as glyphosate and phenoxy herbicides and dicamba herbicides. A lot of slough water in Manitoba, for instance, has very high pH, so the LI700 works better in those areas.

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“I would say Liberate is the safer product. It can be used under a wide range of conditions and still performs in terms of droplet size. But the biggest volume by far is the LI700. It works with insecticides, miticides and other systemics that want a lower pH water.”

Crampton said the half-life of the active product is reduced dramatically if the pH of the water is too high because of alkaline hydrolysis. For example, with dimethylate, if the pH of the water is nine, the half-life of the active component is only 45 minutes.

“In both products, Lici-Tech reduces your driftable fines without increasing the size of the larger droplets. Big droplets either shear or bounce off the leaves. You’re wasting active product because you’re not getting contact.”

Crampton said lecithin-based adjuvants also help a grower get better value for his spray dollar because they are rain fast 30 minutes after application, without damaging the cuticle.

Loveland adjuvants penetrate quicker than synthetic adjuvants and without plant damage simply because they are a plant based product. Company chemists found out decades ago that lecithin was highly effective at penetrating the waxy barrier on plant leaves, he added.

WinField

WinField is in the process of re-introducing prairie farmers to InterLock, said spokesperson David Van Dam.

The product is sprayed on 67 million acres a year in the United States.

In Canada, InterLock has been available for a few years but was not actively promoted. Van Dam called it a re-introduction now because the product will be promoted and distributed by United Suppliers.

“Spray efficacy is all about coverage,” he said.

“You want your pesticide to hit the target whether you’re spraying herbicides, insecticides, fungicides or desiccants. InterLock is designed to resolve that issue and help you put more product on target.”

Van Dam said InterLock holds the solution together enough to prevent fine droplets from forming but does not hold it so tightly that large droplets are produced.

As a result, the sheet of solution coming out the nozzle breaks apart into droplets that are the ideal size.

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WinField won’t say how it does this, but Van Dam said the data shows that it’s true.

Overall coverage averaged 63 percent better than the control field in an aerial application of Idaho potatoes using InterLock and a nonionic surfactant.

Coverage was 36 percent better in the top of the canopy, 86 percent better in the middle of the canopy and 81 percent better in the lower canopy.

Van Dam said the improvement in the top canopy coverage rated no better than moderate because that’s the easiest region to place the product. However, a crop’s enemy is typically lurking in the middle and lower regions, which is where InterLock achieved the greatest improvement in coverage.

“You want those pesticides to hit the target, whether it’s the easy target at the top of the canopy or penetrating further down to the middle and lower portions,” he said.

“It’s more than just penetration. You also want to stop any off-target movement of the spray. That’s product you paid for that you’ve just lost. If you don’t get the best possible coverage, then you’re not getting full value for your money.

“Our biggest competitor on the Canadian Prairies isn’t another deposition agent. Our biggest competitor is the untreated acre, where farmers don’t get full value for the money they spend on crop protection products.”

Van Dam said experience in the U.S. shows that InterLock is an excellent tank mix with desiccants, and there are virtually no tank mix restrictions on the product.

High Activate or Activate Plus surfactants work best with InterLock on the Prairies, he added.

“We always promote the surfactant first in terms of performance and efficacy of the pesticide in the tank,” he said.

“The surfactant goes in to improve the activity of the product. InterLock goes in to improve the coverage.”

Van Dam said InterLock has been used by American aerial applicators for over a decade and is now used by some Canadian aerial applicators.

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  • Denise

    Surfactant POEA is 5X more toxic than glyphosate, so I read.
    pan-international.org/wp-content/uploads/Glyphosate-monograph.pdf