Effect of LibertyÒ application rate, method, and spray volume on weed control in Liberty-LinkedÒ sugar beets

Don W. Morishita and Michael J. Wille

Liberty is a nonselective herbicide currently being evaluated for weed control in transgenic Liberty-Linked sugar beets. Because Liberty does not readily translocate in plants once it is taken up, spray coverage may be an important factor contributing to its efficacy. Studies were conducted in 1998 and 1999 to evaluate Liberty application rate, application method, and spray volume for weed control in Liberty-Linked sugar beets. This report represents the second year of this study. The first year of this study is presented in the 1999 UI Winter Commodity School Proceedings.

The experiment was conducted at the University of Idaho Research and Extension Center near Kimberly, Idaho. Sugar beet (‘8757 LL’) was planted 0.75 inch deep April 15, 1999, at a rate of 47,520 seed/A on 22-inch row spacing and grown under sprinkler irrigation. All herbicides were applied with a CO₂-pressurized bicycle-wheel sprayer. Application methods compared were broadcast, even fan band, and band with air induction (AI) nozzles. The AI nozzles are a relatively new nozzle design manufactured by TeeJet Spraying Systems, Inc. Broadcast applications were applied with flat fan nozzles at 10 and 20 gpa, and both band applications were applied at 20 gpa. All band applications were 10-inches wide. Additional application information and weed densities are shown in Table 1. The experimental design was a randomized complete block with four replications. Individual plots were 4-rows by 30-feet. Crop injury and weed control were evaluated 7 and 28 days after the last treatment was applied (DAT). The two center rows of each plot were harvested with a mechanical harvester September 22.

Table 1. Application information and weed species densities.

None of the herbicide treatments injured the crop at either evaluation date (Table 2). Common lambsquarters control ranged from 88 to 100% for all herbicide treatments 7 and 28 DAT, respectively. Kochia control with all Liberty treatments ranged from 86 to 100% 7 and 28 DAT. ProgressÒ + UpBeetÒ applied in a band or broadcast did not satisfactorily control kochia. Volunteer wheat control with Liberty was similar to that observed for kochia. Liberty at 20.5 fl oz/A applied with AI band nozzles controlled volunteer wheat 73% 28 DAT, however there were no statistical differences among any of the treatments. All of the herbicide treatments had higher sugar beet root yields and more extractable sugar than the check. Liberty applied broadcast or with even fan band nozzles had yields ranging from 16 to 24 ton/A. Root yields of the Progress + UpBeet treatments were lower than the Liberty treatments applied broadcast or even band and equal to Liberty treatments applied AI band. Weed control, root yield, and extractable sugar yield does not appear to be affected by application volume or broadcast versus even fan band application methods. Root and extractable sugar yield appear to be reduced with AI band nozzles.