It is very common for growers to want to tank-mix multiple products when spraying in order to save time and 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 pesticide or fertilizer that you wear the appropriate safety equipment and carefully read and follow label directions. 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 that growers confirm compatibility by performing a jar test.
Be sure to fill the spray tank one-half to three-fourths full of water and have good agitation before adding any product. If the 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. Products that fit into this category are the tins and EBDCs such as the Manzate/Penncozeb-type materials. A de-foaming agent may need to be added first if the tank has foam on top. The foam can cause the powder to cake up and not disperse.
Copper compounds are a common tank-mix partner with fungicides and should be added following the wettable powder-type materials. It should be noted that we do not recommend fungicides for Cercospora leaf spot be mixed or sprayed at the same time with glyphosate and AMS. This is particularly true with some copper compounds, as severe crop injury can occur. Another reason is that recommended water volume and spray pressure are different between the fungicides and herbicide. This may also effect efficacy or drift potential.
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.