HERB AND MSU-HERB FIELD VALIDATION FOR SOYBEAN (GLYCINE-MAX) WEED-CONTROL IN MISSISSIPPI

In 1994, herbicide efficacy and competitive index databases were adjus ted in the soybean herbicide recommendation program HERB to best refle ct data for Mississippi. Field experiments were conducted to compare e fficacy and economics of postemergence herbicides recommended by HERB and MSU-HERB. The study was conducted utilizing four locations over 2 yr, which provided different soil types, weed spectra, and environment al conditions with which to evaluate weed control from herbicides reco mmended by these programs. HERB and MSU-HERB agreed on an herbicide re commendation in 62% of the modeling runs. Herbicides recommended by bo th software versions were generally effective for controlling the pred ominant weed species at each location. In instances where there was a significant difference in herbicide efficacy between herbicides recomm ended by HERB and MSU-HERB, improved weed control resulted from herbic ides recommended by MSU-HERB. In 1994, excellent moisture conditions e nabled soybean to gain a significant competitive advantage over weeds and, as a result, yield loss predictions after treatment were overesti mated in most instances. Conversely, 1995 environmental conditions bet ter represented average Mississippi growing conditions, and yield loss predictions after treatment were more accurate. Yield loss prediction accuracy of KERB versions was related to the length of interference b etween soybean and weeds. Thus, prediction accuracy of HERB and MSU-HE RB was similar. Soybean yield increase and net economic gain following MSU-HERB recommendations was as high or higher than following HERB re commendations.