June 2, 2020 - 8:00am -- lehman.488@osu.edu

Tank mixing of various combinations of pesticides, as well as pesticides plus other liquid products such as biologicals, fertilizers, and plant amendments, is a common practice.  Tank mixing allows for the treatment of various pests, for example weeds and disease, in the same sprayer pass.  Successful tank mixing can save time and money.  However, when tank mixes are not compatible, dollars are lost due to decreased pesticide or product efficacy and in increased time needed to clean out a sprayer. Purdue University Extension has a good buileting entitled "Avoid Tank Mixing Errors" that is available as a pdf download online at https://ppp.purdue.edu//wp-content/uploads/files/PPP-122.pdf.   In this column I am going to summarize some of the major factors responsible for tank mixing errors from that bulletin.

The goal of tank mixing is both product compatibility in terms of a sprayable solution, and retention of product effectiveness.  There are several factors that determine tank mix compatibility including the product formulation, water pH and hardness, the number of products being tank mixed, and the mixing order.  Regardless of the pesticides used in a tank mix, water is by far the largest single ingredient, typically accounting for 90% plus of the total volume.  Both water pH and water hardness can affect spray mixtures effectiveness.  Applicators should know the pH and hardness number of their sprayer water.  Purdue Extension has a good publication entitled The Impact of Water Quality on Pesticide Performance available as a pdf at   https://go.osu.edu/waterqualityonpesticideperf.  If liquid fertilizer is used as the carrier instead of water, this adds an additional consideration due to the high salt content and reduced solubility of products in liquid fertilizer. 

Incompatibility can occur both physically and chemically. Physical incompatibility of a tank mix is visible.  Products will fail to disperse or go into a solution.  Applicators will see the mix separating into layers, products failing to dissolve resulting in sediments or in worst case scenarios, the formation of gels, pastes and clumps.  Chemical incompatibility is often harder to detect in the tank.  These are tank mixes that go into solution, but cause antagonism.  This results in each or some of the products in the tank mix demonstrating decreased effectiveness or poorer control of a target species compared to an application of only that product.  Sometimes chemical incompatibility can be detected by observing a temperature change in the spray mix, usually an exothermic (heating) reaction, a color change and/or the production of gas or odor.

Some common causes of tank mixing mistakes are due to the following: Failure to read and follow label directions regarding tank mixes, combining products in the tank that have not been jar tested, mixes of multiple products/multiple formulations, mixing products in the wrong sequence and mixing products with insufficient water volume in the sprayer tank.

Many pesticide labels have a section on mixing and handling.  Herbicide labels often contain specific information about what other products may or may not be added to a tank mix.  Most often those labels also include a section on how to do a compatibility test if other pesticide products that are not expressly prohibited might be included in a tank mix.  The instructions will essentially spell out how to do a jar test, including the amounts and mixing order of various pesticide formulations.  Note that it is much less expensive and time consuming to find out that a planned tank mix is incompatible while doing a small-scale jar test, than to have an incompatibility problem show up in the sprayer tank.

Mixing order is critically important with tank mixes, especially if they involve a range of formulations from a dry dispersible granule to an emulsifiable concentrate. Start with the tank at least half full of water, then add products by formulation type, agitating and allowing time to go into solution before adding the next product.  Water soluble packets should always be added first.  Dry products should always be added before emulsifiable concentrates or any oil-based product. A good acronym to remember mixing order is WAMLEGS where W= water soluble packets, wettable powders, dry flowables, A= agitation and buffers, M= microcapsule suspension, L= liquids and solubles, E= emulsifiable concentrates, G= high-load glyphosate products and S= surfactants.  

Keep in mind when tank mixing pesticides and other products, that as the number of products added to a tank mix increases, the odds of some type of incompatibility, physical or chemical, also increase.  A final factor affecting tank mixing is water temperature.  Allow more time for mixing with cold water.  Contact the Wayne County Extension office at 330-264-8722 for more information about tank mixing pesticides.

Wayne County Extension IPM Coordinator

Frank Becker has joined the Wayne County Extension office and is working as the Integrated Pest Management Program Coordinator.  Frank will focus on providing service, education and information for commercial vegetable and fruit producers.  Contact Frank by phone at 330-264-8722 or by email at becker.587@osu.edu.