Proper Tank Mixing Procedures

Why Tank Mix in the First Place?

• Combining several products into one spray greatly increases efficiency, which saves valuable time and diesel fuel. Fewer trips across the field also reduces the likelihood of causing soil compaction, which can have a wide array of negative impacts on a crop. Additionally, combining multiple modes of action in the tank can slow the evolution of resistant weeds, pathogens, and insects.
• Another great benefit of tank mixing is the improved performance afforded by including the proper adjuvants. Whether it's a sticker, spreader, drift-reducing agent, or something else entirely, many pesticides would not perform optimally without being combined with the right tank mix partners. Learn more about Spray Adjuvants.

Consult the Literature, Utilize Technology

• The obligatory statement that always arises when discussing pesticides certainly applies to tank mix compatibility as well: Read the label! The pesticide label will have key information on which adjuvants should and should not be mixed with a certain product, whether or not it requires agitation, and which products it should not be mixed with.
• ThePenn State Agronomy Guide also contains valuable information on the do's and don'ts of tank mixing pesticides.
• The MixTank App is a valuable tool for pesticide applicators that can be downloaded on a smartphone or tablet for free or used online.

Always Take a Water Sample

• Before even getting into whether certain pesticides mix well together, it's a great idea to test the quality of your water. "Hard" water contains positively charged cations, which can bind to negatively charged anions in the pesticide formulation, which will decrease the efficacy of the product. Commonly observed cations include calcium (Ca²⁺), magnesium (Mg²⁺), and sodium (Na⁺). If you take a water sample and find that you do have hard water, adding Ammonium sulfate (AMS) to the spray tank solution is a common remedy. For most applications, adding 17 lbs of dry AMS per 100 gal of water should do the trick. The table below provides a basic scale of reference for what constitutes hard or soft water.

*ppm refers to the amount of dissolved cations

• Water pH can have a tremendous impact on how a pesticide will perform. Due to the wide range of variability of pesticides, the optimal pH for the spray tank formulation is somewhat of a moving target. For example, a fungicide such as Captan will last the longest at a pH of 5, which is fairly acidic. Conversely, the insecticide Sevin (carbaryl) lasts the longest at a neutral pH of 7. Be sure to read your pesticide label to determine what spray tank pH you should be aiming for. pH buffers can always be added to the tank to achieve the desired pH level.
• If you aren't sure about the quality of the water you use in your pesticide spray tank, then consider having your water tested by the kind folks at the Penn State Ag Analytical Services Laboratory.

Proper Mixing Order is Crucial

• Make sure to add the components of your desired tank mix in the order listed below:

1. Fill the tank halfway full with clean water. Donot pour concentrated pesticide directly into an empty tank
2. If the pesticide calls for the use of AMS, then add that after the water.
3. Water dispersible products such as wettable powders (WP) and dry flowables (DF) go next. It's a good idea to pre-slurrythese products before adding them to the tank.
4. Agitate the tank until all products have formed a solution.
5. Microcapsule suspension products go in next.
6. Liquids and emulsifiable concentrates
7. The final thing that goes into the tank is the surfactants. Any necessary non-ionic surfactants, crop oil concentrates, or methylated seed oils will go in here at the end.

Physical Incompatibility

• Everyone knows that oil and water don't mix, and unfortunately, some pesticides don't mix well either. In situations where two products are physically incompatible, applicators may observe layer separation (settling), gel formation, failure to disperse, or clumping of solids. For example, if a dry product such as a wettable powder is added to the tank immediately after an oil-based product, the powder may bind to the oil and fail to hydrate. Conducting a basic jar test can be a simple and effective way to determine if a unique mixture of products will play well in the spray tank.