Tank-mixing herbicides and other agrichemicals is a necessary practice to increase weed control and use machine hours wisely. Unfortunately, the likelihood of physical incompatibility increases as the number of products added to a tank-mix increases. This article will give a brief overview of the principles of tank-mix order for herbicide applications. Product labels are the ultimate authority on the mixing order, so be sure to check the mixing instructions on products and combinations of products you have not used before. If the label is unclear, a jar test is a great alternative to a ‘tank test.’ Guidelines for conducting a jar test are included at the end of this article.

Remember, herbicides need to ‘get wet’ in order to be applied through the spray. Meaning that herbicides must be dissolved or suspended in the carrier water. It might be helpful to think of a spray tank like a swimming pool. A pool can only hold so many kids, and a tank of water can only hold so many molecules that aren’t water. Also, the first kids to enter the pool have more room to swim and get wet compared to the last kids to enter the pool. Pesticides are somewhat similar – it’s easier to dissolve a product in “clean” water compared to water that has already had herbicides added. This means that the most difficult-to-dissolve herbicides should be added first, and the pesticides that are easiest to dissolve should be added last. Specific chemical reactions can change this order in some mixes, for example, adding the volatility reduction agent first when applying XtendiMax or Engenia – this is why it’s important to check labels and do jar tests. But, in general, a “safe” mixing order is listed in Table 1. 

Table 1. Generalized mixing order based on type of formulation.

One specific product that is often discussed in mixing order discussions is AMS. When AMS is being used as a water conditioner, such as with glyphosate products, it should be added to the tank first. But if AMS is being used as a nitrogen source to increase herbicide uptake, as with Sharpen, it does not have to be added first.

Using label-recommended mixing orders is the best way to avoid a tank-mix mishap, but there are a few other factors that could be adjusted to improve mixing. The simplest would be to wait until one product is thoroughly mixed before adding the next product. Another simple suggestion is to add a larger volume of water before adding products (make the pool bigger to continue the analogy above). In addition, warmer water will usually help products mix more quickly. But that is difficult to control, so the best thing to do is to be aware that longer agitation times between added products might be necessary when water is colder.

If you use a new-to-you combination of products, consider doing a “jar test” before loading the sprayer. The steps for a jar test are:

1. Put one pint of the carrier you will use in a 1-quart jar.
2. Add products in the ratio and order you’ll use in the spray tank.
3. Cap the jar and mix.
4. After 30 minutes, check the jar for components that have separated, settled, or are otherwise undesirable for spraying.

Tank-mixing was discussed in an episode of the War Against Weeds podcast. The recording is available here. 

The use of trade names is for clarity to readers and does not imply endorsement of a particular product, nor does exclusion imply non-approval. Always consult the herbicide label for the most current use requirements.

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