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Water Conditioners for Glyphosate Applications   
by
Bob Hartzler

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January 26, 2007AMS (ammonium sulfate) is widely used with glyphosate to enhance its performance. AMS is different than other spray additives (surfactants, crop oil concentrates, etc.) in that AMS is primarily active in the spray tank (negating the effect of antagonistic salts) rather than at the leaf surface. While AMS is a cost-effective means of counteracting the negative effects of antagonistic salts in water, many applicators desire alternatives due to the inconvenience of handling and dissolving AMS in the spray tank. A variety of products, often referred to as water conditioners, have been introduced as AMS substitutes in order to avoid the problems associated with handling AMS.

Water conditioners typically contain a number of ingredients, including AMS, surfactants, anti-foaming agents, etc. University research has shown that not all water conditioners are as effective as AMS at protecting glyphosate performance when hard water is used as the carrier. Differences in performance among conditioners probably are related to how much AMS is found in the product. Spray additives are not regulated, thus manufacturers are not required to provide specific information regarding quantities of AMS or other active ingredients found in the product. Because of this, it is difficult, or impossible, to know exactly how much AMS the water conditioner provides.

The influence of AMS and several water conditioners on the efficacy of glyphosate against velvetleaf was evaluated using either distilled water (no cation) or water with 160 ppm Fe added (Figure 1). In the absence of antagonistic cations, all additives provided velvetleaf control equivalent to or better than glyphosate alone. However, when hard water was used as the carrier (Fe added), several of the products were less effective than AMS at eliminating the effect of the antagonistic salts, and two products actually resulted in poorer control than glyphosate alone.

The reason for water conditioners failing to perform as well as AMS in hard water is probably due to them containing an insufficient quantity of AMS. The solubility of water in AMS is 5.9 lb/gal at 32 F, but since water conditioners contain other ingredients they always contain less AMS than 5.9 lb/gal. Typical use rates of water conditioners are 0.25 to 1% v/v. Thus, if a conditioner contained 4 lb AMS/gal and was applied at a rate of 1% v/v, it would apply the equivalent of 4 lbs/100 gal. Most glyphosate products recommend 8.5 to 17 lbs/100 gal, thus water conditioners provide much lower rates of AMS than recommended on glyphosate labels.

So, what's the bottom line on conditioners? In situations where hard water is used as a carrier, many water conditioners may not be as effective as AMS at eliminating the antagonistic effect of Fe, Ca, Mg and other salts. However, most water sources in Iowa contain relatively soft water and the full rate of AMS is not required to counteract antagonistic cations. Thus, water conditioners may sufficiently counteract negative effects of the carrier due to low levels of antagonistic cations. The only way to determine whether a water conditioner is appropriate is to determine the hardness of the water used as a carrier and the amount of AMS in the specific product.

Acknowledgement: Much of the information and data in this article was adapted from an article prepared by Mark Bernards, Extension Weed Specialist at University of Nebraska.
Mark L. Bernards. 2007. AMS - What is it doing in my tank? Proceedings 2007 Crop Protection Clinics. University of Nebraska-Lincoln.

 

Prepared by Bob Hartzler, extension weed management specialist, Department of Agronomy, Iowa State University

For more information contact:
ISU Extension Agronomy
2104 Agronomy Hall
Ames, Iowa 50011-1010
Voice: (515) 294-1923
Fax: (515) 294-9985
http://www.weeds.iastate.edu
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