Pesticide Safety… “I should know this.”

Jennifer Weber, University of Arizona Pesticide Safety Education Program

Welcome to the second edition of the

Pesticide Safety… “I should know this” series, where we will answer pesticide-related questions that seem to stump the best of us.  

Compatibility Jar Tests. Why Can’t We All Just Get Along?

I am happy to note we have another topic for the Pesticide Safety… “I should know this” series, where we answer pesticide-related questions and provide safety information you can pass along to others.

Request: I went to your “Measuring and Mixing Pesticides” presentation during the Yuma Ag Summit. I liked the jar test activity. It showed the importance of testing out the products you want to mix together to make sure they are compatible before you load them into the tank. Will you write a short article about jar tests? I think pesticide handlers should know this.

I am glad you liked the tank mixing demo and I want to thank you for the great article suggestion. How to perform compatibility jar tests before tank mixing is a perfect topic for the Pesticide Safety… “I should know this” series.

I’ll start by providing a bit of background about tank mixing and compatibility concerns to bring readers up to speed with your request. I’ll wrap up the article with jar test instructions. 

Background. Tank mixing is when two or more pesticides are mixed together for a single application. Tank mixing is convenient and can save time, money, and fuel if applying with an ATV or tractor.

You can purchase prepared tank mixes (often referred to as premixes and prepacks) or you can mix products together yourself. However, not all pesticides are physically or chemically compatible.

Incompatibility could cause ingredients to gel, clump, separate or become less effective. Other mixtures create problems inside your spray tank, such as the formation of heat, gas, or precipitation; or result in damage to plants treated with the products.

A great source for compatibility information is the pesticide label. Some labels include details about specific combinations known to be incompatible, including problems that could occur when adding adjuvants, such as spreaders, detergents, or drift reducing agents. Other labels contain more general compatibility statements and jar test recommendations.

Not all labels include tank mixing guidance or restrictions. However, the lack of such statements doesn’t give you the green light to mix away to your heart’s content. You are responsible for performing a jar test to ensure compatibility, even when the label doesn’t list a potential problem.

A jar test is quite simple. It’s a small-scale tank mixing practice run, which allows you to see what could potentially happen if you combined the same products in your spray tank. The steps are the following:

  • Put on the personal protective equipment listed on the label to protect yourself from splashes or spills.
  • Fill a small glass or plastic jar with water or other carrier (often fertilizer) until it is 20-50% full.
  • Add products one at a time in proportionate amounts and in the proper order (a perfect topic for another article).
  • Lightly mix, swirl, or shake the contents in the jar.
  • Look for incompatibility issues, such as heat, precipitation, ingredient separation, or clumping.
  • Let the mixture sit for 10-15 minutes and check it again for any changes.
  • If nothing happens and the mixture appears consistent, it is probable the products are chemically and physically compatible.
  • Don’t forget to test the mixture out at the site for performance and plant damage issues.

I realize this article is an extremely brief response to the request for a description of compatibility jar tests.  If you would like to dive deeper into the topic of tank mixing, jar tests, compatibility concerns, and solutions, I have a great resource recommendation. The Purdue Pesticide Program produced a booklet called, “Avoid Tank Mixing Errors.” It is available as a pdf on the webpage:

Is there something you know you should know, or would like others to know?  If so, send me your requests and questions by email or phone (602) 827-8222. I’ll be happy to add them to the Pesticide Safety… “I should know this” series.

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