how to measure phytotoxicity of newer herbicide.
Outside United States
I'm not sure what you mean by measuring phytotoxicity. The labeled rate usually is a good measure of the phytotoxicity. The labeled rate generally is the minimum dose that will provide consistent weed control under a range of conditions.
One method commonly used is to construct dose response curves. This paper describes the method:
Knezevic, S. Z., P. H. Sikkema, F. Tardif, A. S. Hamill, K. Chandler, and C. J. Swanton. 1998. Biologically effective dose and selectivity of RPA 201772 (isoxaflutole) for preemergence weed control in corn (Zea mays). Weed Technol. 12:670–676.
Oops, wrong article, this is the one I was referring to:
Knezevic, S. Z., J. C. Streibig, and C. Ritz. 2007. Utilizing R software package for dose-response studies: the concept and data analysis. Weed Technol. 21:840–848.