Select and handle ammonium sulfate products properly when preparing glyphosate spray mixes

Reports from farmers indicate potential troubles with plugged sprayer screens.

Using spray grade ammonium sulfate (AMS) is a recommended practice when mixing glyphosate solutions for field application. Seventeen pounds AMS per 100 gallons of water is recommended. AMS will overcome water hardness and provides enhanced glyphosate effectiveness on weeds with natural barriers for glyphosate, such as velvetleaf and lambsquarters. “Spray grade” indicates a very pure, finely processed product intended for solution in a spray mixture. Liquid AMS is gaining in popularity and is equally effective if properly used, but is considerably more costly than dry spray grade AMS. Other forms of ammonium sulfate, like granular fertilizer, which are not intended as pesticide spray components, should never be used.

Undissolved AMS can become a problem in the sprayer, plugging screens and possibly nozzles. If using ammonium sulfate, add it slowly through the strainer screen into the tank. Continue agitation. Ensure that dry ammonium sulfate is completely dissolved in the spray tank before the addition of other products. Michigan State University weed scientists recommend always adding AMS first. The AMS acts as a water conditioner. Following thoroughly-dissolved AMS, other herbicides should be added in proper sequence, followed by adjuvants such as surfactants or crop oils.

Some farmers mix the spray grade ammonium sulfate into a concentrate, or “slurry,” in a clean container, then add it to the spray tank.

Sediments suspended in spray water also cause reduction in glyphosate effectiveness. Glyphosate binds to suspended sediments, rendering them unavailable for plant uptake. Farmers should avoid mixing glyphosate products with water from ponds or ditches that is visibly muddy or murky.

For more information on the importance of water quality with regard to pesticide spraying operations, review the Purdue University publication “The Impact of Water Quality on Pesticide Performance.”

For more information, contact Jim Isleib, MSU Extension crop production educator at 906-387-2530.

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