Editor's Note: This column is part one of a two-part series. Part two will publish in the June issue.



Those who have dealt with any form of agricultural production in the past three decades will undoubtedly have had some experience with glyphosate. The impact of this herbicide since its introduction in 1972 has been monumental. Its originator, Monsanto, used Roundup Ready technology to launch the first widely grown genetically modified crops worldwide. Although some crops have not yet benefited from Roundup Ready technology commercially, many industries still utilize glyphosate both for weed control and in some cases, as with sugarcane, growth regulation and ripening. We can learn much from other commodities that use glyphosate so extensively.



Understanding Glyphosate
Glyphosate is an acid and is very similar in molecular nature to glyphosine, a natural amino acid. Because an acid is a negative ion (anion), it is formulated as a salt. Originally, glyphosate was often formulated as an isopropylamine salt. The isopropylamine cation is rather "bulky," and limits the amount of glyphosate that can be formulated in a given volume of product.



Lately, we have seen a trend to formulate glyphosate as salts other than the isopropylamine salt so that more glyphosate acid can be formulated per gallon. Simply put, the lower the molecular weight of the cation portion of the salt, the more "room" for glyphosate acid per gallon.



Monsanto and many of its competitors are moving toward a potassium salt so that up to six pounds active ingredient per U.S. gallon can be formulated into the final product. Having more concentrated formulations reduces packaging costs and allows for easier handling on the farm operation.



Some manufacturers have implied that the salt formulation affects the activity of the herbicide. In early research comparing glyphosate formulations in glyphosate tolerant soybeans, some increased injury was detected when the trimesium salt formulation was compared to the isopropylamine salt. The trimesium salt caused some superficial burning of foliage, similar to fertilizer salt injury. But for the most part, the activity of glyphosate within the plant is not affected by the salt.



Calculate Rates Accordingly
With so many generic glyphosate formulations on the worldwide market, it is very important to convert rates of application correctly. Since products contain different glyphosate concentrations per gallon, rates should be adjusted according to acid equivalency, not pounds active ingredient. Pounds active ingredient comprises the weight of both the glyphosate acid AND the salt. Pounds acid only pertains to the weight of the glyphosate acid in the formulation.



In the second part of this series, we'll discuss adjuvants and additives to glyphosate as it relates to water quality.



Blaine J. Viator is an independent crop consultant with Calvin Viator, Ph.D. and Associates, LLC. He is an active member in the Louisiana Agricultural Consultants Association, National Alliance of Independent Crop Consultants and the American Society of Sugar Cane Technologists. For correspondence, e-mail bviator@charter.net.