You mix up chemicals and fill the sprayer. You turn it on and what drips out of nozzles looks like mayonnaise. So, you look in the tank. What you see resembles cottage cheese. You pull a hose off the boom supplying nozzles, and it is plugged with the white substance. What went wrong?

Obviously, something you added didn’t “play nice” with something else in the mix.

“If you are just using water as carrier, you probably won’t have these problems,” says Aaron Hager, University of Illinois Extension weed control specialist. “When you begin mixing multiple herbicides or use nutrients as the carrier, it is more likely these problems could show up.

“If you are mixing several things or mixing herbicides and other carriers, performing a jar test first should be standard practice today. It allows you to see how products will mix with each other on a very small scale, instead of finding out when you put them into a whole tank of spray.”

Fred Whitford, director of Purdue Pesticide Programs, notes that while this is good advice, many farmers don’t take the time to do it. “Yet they find time to clean out the sprayer and remove the mess,” Whitford says.

Think about spray mix compatibility

Jeff Nagel, a field agronomist with Keystone Cooperative near Lafayette, Ind., works with farmers to avoid these problems. He notes that perhaps you’re using a generic herbicide this year because it’s cheaper, and it may not have the same adjuvants and surfactants as products you’ve used before. That can affect compatibility.

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“We also have more growers applying sulfur, and some sulfur products have mixing issues in certain cases,” Nagel says. “We have done quite a bit of jar testing recently, often for people who are applying sulfur. We want to make sure what they’re adding to the tank won’t cause problems.”

Nagel developed his own calculator tool to make sure he mixes products in the same ratio in jar tests as in actual spray solution. It takes some math to ensure you are conducting a fair test, he notes.

Jar test how-to

“A jar test simulates what occurs in a tank-mixture and will provide evidence of physical incompatibilities such as separation, settling, inversions and oil residue buildup,” Whitford explains. He published a booklet, “Avoid Tank-Mixing Errors,” PPP-122, which covers the basics of conducting a jar test. Download it for free.

“Even if you’re making the ‘same’ tank-mix you’ve always prepared, you should still conduct a jar test to help identify potential compatibility issues that may occur with even slightly different inert ingredients,” Whitford says. He says even slight adjustments could affect compatibility of a product with others in the tank-mix. If you change water sources and the pH or hardness is different, that also could affect the mixture.

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Pesticide labels often include information about how to conduct jar tests, Whitford notes. Commercial kits are available. Find the kit highlighted in PPP-122 at precisionlab.com.

The University of Nebraska also offers publications, videos and a step-by-step jar test calculator at pested.unl.edu.