An adjuvant is a product that is added to a spray mixture to change its physical or chemical characteristics.
“Adjuvants are designed to maximize a crop protection product’s ability to function by minimizing the constraints in a pesticide application process,” says Dale Ziprick, product manager with UAP.
There are several different adjuvants and they have many different purposes, but they basically fall under two categories as defined by Canada’s Pest Management Regulatory Agency (PMRA).
Activators are the first category. Activators, such as surfactants and crop oils, are designed to enhance the activity of pesticides, for example to improve coverage and increase plant uptake.
The second category, utility modifiers, change the function and physical characteristics of the chemical. This would be done, for example, to reduce foaming, increase solubility, modify pH or reduce spray drift.
Some adjuvants are built into the chemical formulation, so they come in the jug. But sometimes, for various reasons, the adjuvant cannot be built in and must be added by the farmer or spray applicator according to the label specifications.
When mixing adjuvants into products on the farm, farmers should follow those label instructions carefully and make sure they add the right amount, says Tom Wolf, a research scientist with Agriculture and Agri-Food Canada at Saskatoon “Most adjuvants work on the basis of a concentration. If you don’t add the correct rate it won’t work. Adjuvants are also product specific. There isn’t a universal adjuvant that helps all pesticides.”
Surfactants are the most common type of adjuvant. They’re used to improve performance, particularly of herbicides, in a variety of ways. They can ensure better coverage by increasing spreading on the leaf surfaces, improving adhesion properties and enhancing plant uptake.
Adding a surfactant to a herbicide formulation reduces the surface tension of the water and also improves its ability to mix with oily substances. This allows the herbicide to more effectively move through the cuticle — the waxy layer that covers the plant’s leaf surfaces and can inhibit absorption of the herbicide into the plant tissue.
The most common type of surfactants are non-ionic, which are usually alcohol based. There are also methylated seed oils derived from crops such as corn, soybean, sunflower and canola.
Adjuvants are probably one of the most highly researched products in agriculture. There are hundreds of companies worldwide seeking to improve the performance of various pesticides through the use of adjuvants.
Making claims about the efficacy of adjuvants is, however, something that is regulated quite differently in Canada than it is in the U.S.
In the U.S. there are few regulatory requirements for adjuvants. As long as they contain ingredients which are known to be non-toxic they do not have to undergo any efficacy or toxicological testing. In Canada, on the other hand, the PMRA requires performance data.
“In other words if you make a claim on the label that says, ‘if you add this surfactant to a herbicide you improve performance by this much,’ PMRA wants to see the research data that proves it,” says Wolf.
As a result Canadian farmers don’t have access to the same number of adjuvant product lines that Americans do, but they can be reasonably assured that research has been done to support the claims made on the product labels.
Loveland Products Inc. is one of the few companies in Canada selling after-market adjuvants for on-farm use. Loveland has developed a soybean-derived technology called Leci-Tech, which it employs in its LI700, Liberate and MSO (methylated seed oil) surfactants and in Valid, its drift reduction and deposition aid.
LI700 is the only adjuvant product in the Canadian marketplace that can currently make a number of claims on its label that relate to improving the efficiency of herbicides such as glyphosate.
An important claim that LI700 makes is its ability to help reduce spray drift. Independent studies in Canada and globally have generated data that demonstrates LI700’s Leci-Tech technology reduces the percentage of driftable fines in a herbicide application by 50 to 60 per cent when the product is used at the recommended rate and creates a more uniform spray droplet distribution.
LI700 also lowers (acidifies) the pH of the water — that enhances the uptake of some common herbicides like glyphosate. Glyphosate is a negatively charged molecule that tends to have a hard time penetrating the cuticle or oily surfaces of plants. Lowering its pH can reduce the strength of the negative charge, which makes it makes it easier for the herbicide to cross these barriers.
Leci-Tech surfactants enhance adhesion by altering the physical properties of the spray mixture so it sticks to plant surfaces and has properties that enhance product penetration while reducing the risk of crop injury.
“Leci-Tech technology opens up the waxy cuticle to allow for at better and more rapid penetration into the plant,” says Ziprick. “Most penetrating surfactants physically alter the cuticle to open it up, stripping away that cuticle layer and opening up the leaf surface for penetration. They work great too, but there can be an appreciable risk of crop injury as a result.”
Currently LI 700, Liberate and MSO with Leci-Tech are available in a 2×10-litre case size. LI 700 will also have a new 4×3.78-litre case for 2013. The drift reduction and deposition aid Valid comes in a 3.7-litre jug size.
Other new technology
Syngenta Canada Inc. also has a new adjuvant that comes in the jug and claims to offer benefits for producers. The company’s Axial herbicide is now available in a new formulation with a built-in adjuvant for control of wild oats, green foxtail, yellow foxtail, barnyard grass, volunteer oats, volunteer canary seed and proso millet in spring wheat and barley.
According to the company’s recent press release, the new adjuvant has a unique action on pinoxaden — the active ingredient in Axial — which increases uptake versus standard crop oil concentrate (COC) or methylated seed oil (MSO) type adjuvants.
“This all-in-one Axial formulation makes it more convenient and easier to apply,” says Jon Habok, asset lead, cereal herbicides for Syngenta Canada in the release. “Growers will no longer need to mix products to get the effective grass weed control they are looking for in spring wheat and barley.”
The all-in-one formulation will be available in 2013 for western Canadian farmers. It will come in a 2×10-litre case, which treats 40 acres, an 80-litre drum, which treats 160 acres, or a 400-litre tote, which treats 800 acres.
Ammonium sulphate as an adjuvent
Spray water quality is another critical factor that can influence the performance of some pesticides. These characteristics include pH, water hardness and the presence of bicarbonates. Much of the well water used in Western Canada is hard, which means it has an elevated concentration of the cations, mainly calcium and magnesium.
“Some herbicides are antagonized by hard water,” says Wolf. “The calcium and magnesium will typically bind with a herbicide and render it inactive. But bicarbonate, iron, and water cleanliness also play a role — these are not measured by water hardness.”
Ziprick advises farmers to measure the hardness of the water they will be using for spray applications and understand how the chemicals they’re using may be susceptible to that water quality. “You then have a template to decide which pesticide and adjuvant to use depending on hard water levels, high pH or other spray quality factors,” he says. “It’s been well documented that any form of glyphosate can be compromised by hard water. It’s just like conducting a soil test, if you don’t measure it you can’t manage it.”
In the U.S. it is common practice for farmers to use ammonium sulfate as an adjuvant for glyphosate and glufosinate herbicides. “It’s not on all labels and it may or may not show a benefit but many custom applicators put it in as a form of insurance [against hard water issues],” says Wolf. Farmers should be sure, he adds, to use the right form and not ammonium thiosulfate, which can form a precipitate in the tank, plugging nozzles.
Alternative water conditioning products do exist, like Loveland Products’ Choice Weathermaster, which also works to tie up positive cations and is added to the water prior to adding the herbicide.
Ziprick explains that calcium is generally the biggest cause of hard water found in most samples in Western Canada and ammonium sulfate does a very good job of addressing it, but magnesium. Iron can also be a concern, and iron especially can have a strong affect on glyphosate even at low concentrations. “Choice Weathermaster has chelating and sequestering agents that bind to all forms of cations, so if you aren’t sure of exactly what you are dealing with I see Choice Weathermaster as a better risk management tool to overcome all forms of cation concentrations in a water sample as a water conditioner,” he says.
Adjuvants for tank cleaning
Just as there are adjuvants to help with the functionality and performance of pesticides there are also adjuvants that help clean them out of the tank after application.
There are two basic formulations of pesticides: water soluble and oil soluble. Oil-based pesticides can be particularly hard to clean out because they can stick to plastic walls and are difficult to wash off. “It’s really important to take the time and effort to clean [the sprayer] out properly,” says Ziprick. “The payoff is obvious when crop injury is prevented by a relatively simple task.”
Traditional tank cleaning products often have an ammonia base, which is effective against many herbicides, but not all, says Ziprick. “Our All Clear product contains surfactants as well as sequestering agents that do not allow for re-deposition and do a real good job of getting into the nooks and crannies and the corners of the entire spray application equipment.”