Herbicide rates have become progressively lower over the last several years. Some of the older products are still applied at high rates although the rates for many of the newer products are much lower. Rates range from an ounce or less up to 1 to 2 gallons per acre. New active ingredients, formulations and application technology are the main reasons for these reduced rates.

It takes many years and millions of dollars to develop a new herbicide and many never make it to market. Rates are established during this developmental stage. They start in the laboratory and greenhouse, move to field research stations then to grower fields and eventually make it to market. Rates often undergo significant adjustment during this period. For Instance, when we first received Pursuit herbicide for testing it was a numbered compound (AC 263,499) and we applied it at 16 oz. per acre. The use rates were eventually established at 2 to 6 ounces. It is necessary during this developmental stage to compare very small differences in rate and research reports can report on differences of a fraction of an ounce per acre. Transferring this research from single plants in the greenhouse or small plots at a research station to hundred-acre fields is a challenge. Compounds for research trials are often measured with syringes and gram scales while commercial field applications are measured in buckets or half gallon containers. Commercial application rates are sometimes adjusted to fit container or field size. Comparing small scale research to large scale commercial applications is like measuring with a micrometer and cutting with an axe.

To contact Barry Tickes go to: btickes@ag.arizona.edu.

For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.