Over 100 pesticide labels recommend the use of a spray adjuvant to enhance efficacy of the active ingredient. Many of these labels require the use of an adjuvant. Imazethapyr requires not only the use of a nitrogen-based fertilizer, but for some applications, the use of a crop oil concentrate. The crop oil concentrate requirement specifies a given volume of adjuvant per hectare. The wetting properties, and/or surface chemistry, play a vital role in the usefulness of the crop oil concentrate.
There are several methods of evaluating the surface activity of adjuvants. Contact angles at the liquid-solid interface, surface tension, both dynamic and static, and spread areas are among the methods that have often been used to determine the effectiveness of an adjuvant. While these measurements do not replace actual efficacy trials, they should be valuable in the screening of different adjuvants for suitability with any given pesticide spray.
A series of tests were designed to determine if surface chemical properties are appropriate indicators for predicting the usefulness of crop oil concentrates with the herbicide imazethapyr. A correlation between the various methods of evaluating surface activity and the actual efficacy enhancements was observed.
When spray volumes per hectare are decreased, the rate of adjuvant per hectare remains constant and the concentration of the adjuvant increases. Therefore, it was investigated whether the recommendation of a crop oil concentrate at a given rate per hectare was more beneficial with lower spray volumes.
In these tests, the increased rate of adjuvant did not improve surface activity, or herbicide efficacy.