This time of year, farmers are spraying and praying at a rapid pace.  However, the need for speed can sometimes lead to hasty decisions.  To save trips across the field, it is very common for growers to tank-mix EVERYTHING! 

In many cases, tank-mixes are fine, but there are times when pesticides are physically incompatible or the combination of products can result in reduced performance and/or increased crop injury.  Collectively, I have termed these problems the tank-mix blues (Figure 1).

Over the years, I have seen and heard of some interesting tank-mixtures.  On numerous occasions, I have been witness to undesirable peanut injury from spray-tank cocktails that have contained five or more different products (Figure 2). 

Interestingly and incorrectly, herbicides usually get most of the blame for the problem.  Crop response to any tank-mixture will depend upon several factors including the chemicals, GPA, air temperature, time of day, relative humidity, leaf wetness, and overall crop health.  That is why accurately predicating the final outcome of many tank-mixtures is almost impossible. I discussed the peanut tank-mix blues more thoroughly in a previous Tailgate Talk article (June 21, 2016).

Here are a couple of points to consider when tank-mixing agrichemicals based upon my observations:

Speaking of mixing order, the general formulation science mixing order is as follows: 1) water soluble bags (WSB); 2) water soluble granules (WSG); 3) water dispersible granules (WG, XP, DF); 4) wettable powders (WP); 5) water based suspension concentrates/aqueous flowables (SC, F); 6) water soluble concentrates (SL); 7) suspoemulsions (SE); 8) oil-based suspension concentrates (OD); 9) emulsifiable concentrates (EC); 10) surfactants, oils, adjuvants; 11) soluble fertilizers; and 12) drift retardants.

For those Millennials out there who cannot eat, sleep, or breath without their cell phones, there is an app called Mix-Tank (Precision Laboratories) that you might find useful (http://www.mixtankapp.com/). There are likely some other phone apps out there that I am not yet aware of but probably will be after this article is published.  If you are not phone or computer savvy, a simple jar test is another quick and easy way to alleviate potential tank-mix blues caused by physical incompatibility.

There are some unique situations where the above general mixing order would not be correct.  For example, when tank-mixing Reflex (fomesafen) + Gramoxone (paraquat), the following order should be followed: 1) add 1/2 of the required amount of clean water into the spray tank; 2) start up and maintain tank agitation: 3) add NIS; 4) add Reflex; 5) add Gramoxone; and 6) add remaining amount of clean water. 

Here is another unusual mixing example.  When tank-mixing Halex GT (mesotrione + s-metolachlor + glyphosate) and atrazine, the following mixing sequence should be followed: 1) add 1/2 of the required amount of clean water into the spray tank and start/maintain agitation; 2) add AMS (only if water quality sample indicates the need); 3) add NIS; 4) add atrazine (make sure atrazine is fully dispersed before adding other products); 5) add Halex GT; and 6) add remaining amount of clean water.

Tank-mixing pesticides, fertilizers, and other agri-chemicals is a great way to save time and money. If you are uncertain about a potential pesticide mixture, the tank-mixes blues can be avoided by conducting a simple jar test, using higher water volumes, following the proper mixing order, limiting the number of chemicals added to the mixture, avoiding applications when weather conditions are unfavorable (cold/wet or hot/dry), and studying all products labels.  Your local county extension agent and pesticide purveyor may also be able to assist. 

As always, good weed hunting!