It is common for growers to want to tank-mix multiple products when spraying in order to save time, application cost or for resistance management. In many cases, products can be combined in the spray tank if a proper mixing order is followed. It is important when mixing any type of pesticides or fertilizers that you wear the appropriate safety equipment and read and follow label directions carefully. If there are known interactions or compatibility issues they will be stated. Be aware it would be impossible for the label to advise on all possible tank-mix combinations and interactions, so be cautious. It is recommended before mixing multiple chemicals or fertilizers, growers should confirm compatibility by performing a jar test.
Be sure to fill spray tank one-half to three-fourths full of water and have good agitation before adding any product. If mixing procedure is stated on the label, then follow as instructed. Generally in order to minimize nozzle plugging, the harder-to-mix products should be fully dissolved before the next product is added. The hard-to-mix products are water soluble packets and wettable powders that include dry flowables and water dispersing granules. A de-foaming agent might need to be added first if the tank has foam on top. The foam can cause the powder to cake up and not disperse.
Make sure all pesticide products are added one at a time. If two products are added at the same time, you could have some congealing of the concentrates. Generally, wettable powder and dry flowables or water dispersing granule products should be added first, followed by flowable and microencapsulated products. Add emulsifiable concentrates next followed by any solution or soluble powder products. Any crop oils or surfactants should be added last.
Some spray materials are difficult to keep in suspension. Good agitation and a compatibility agent may be needed to insure uniformity. Prepare only enough products that can be used in one day. It is not advisable to leave spray in the tanks overnight; it may separate out or have adverse effect on efficacy.
Stacy Campbell is a Kansas State Research and Extension agent in Hays for the Cottonwood Extension District Office.