Chlorophyll Fluorescence — A Noninvasive Technique for Rapid Investigation of the Effects of Adjuvants on Herbicide and Plant Growth Regulator Uptake by Leaves

Chlorophyll fluorescence measurements were used to investigate aspects of uptake by wheat leaves of the photosynthetically active herbicide diuron, the amino acid biosynthetic inhibitor herbicide glyphosate, and the plant growth regulator (PGR) chloromequat. Quantitative changes in fluorescence, detected within 60 min of treatment, correlated directly with the concentration of diuron incorporated into leaf tissue. Subsequent fluorescence studies demonstrated that the formulation with Tween 20 enhanced diuron uptake. Further enhancement of diuron uptake by removal of the epicuticular wax layer was unaffected by Tween 20. Maximum uptake of diuron was achieved with Tween 20 concentrations near its critical micelle concentraction (cmc) value. Fluorescence measurements were also used for the rapid selection of the most effective formulations of the photosynthetic herbicides (phenmedipham and bentazon) with commercial adjuvants. Chlorophyll fluorescence emitted from young wheat leaves showed perturbation 24 h after treatment with the nonphotosynthetic herbicide glyphosate and the PGR, chlormequat. Rapid selection of the most effective adjuvant formulations of these compounds was also demonstrated using fluorescence measurements. The results demonstrate that chlorophyll fluorescence measurements can be used to investigate and optimize herbicide and PGR uptake by leaves as well as for the rapid screening of different adjuvant formulations of herbicides and PGRs.