Evaluation of Screening Techniques for Woody Plant Herbicide Development

Woody plant herbicide screening techniques were evaluated in an attempt to expedite the screening process and decrease amounts of herbicide active ingredient required. Rapid greenhouse screening of woody plant seedlings was performed in less than six months while rapid seed screening was performed in less than twenty days. A traditional field screen, requiring ten months, was performed for comparison purposes. Leaf area – biomass ratios were also examined for their influence on herbicide efficacy. Linear regressions were performed using traditional field screen data as the dependent variable and rapid screening technique data as the independent data.

Rapid screens using triclopyr produced more statistically significant regressions compared to those involving imazapyr. Significant regressions were produced that could predict field response of several species using both herbicides and either rapid screening technique. This indicated that rapid screening techniques could determine herbicide efficacy and/or species spectrum of control in much less time with much less herbicide. Rapid seed screens could estimate species spectrum within five days after treatment. The rapid greenhouse screen and rapid seed screen techniques can provide woody plant herbicide developers initial efficacy and spectrum of control data in a cost- and time- effective manner.

Testing showed that as woody plants mature from seedling to sapling, there is a decrease in the leaf area — total aboveground biomass ratio. The decrease in this ratio consistently decreased efficacy of both imazapyr and triclopyr at the lower active ingredient rates. Seedlings with the higher leaf area – biomass ratio had, on the average, higher efficacy response rates to herbicide treatments.