The symptoms these plants exhibit show how the herbicide affected a specific biochemical or metabolic process. Modes of Action Growth inhibitors prevent plant cell growth. Photosynthesis inhibitors stop the process of using light energy for plant growth and development. Amino acid inhibitors prevents plants from making three essential amino acids. Cell disruptors dry out the above-ground plant parts they contact.
Growth regulators mimic naturally occurring plant hormones and cause uncontrolled growth.
Incorporated into the soil before the crop is planted, and by definition, before weed emergence. Applied after the weed emerges from the soil. Applied in a band where the weeds are, not to the crop itself. Curling or bending of plant parts. Yellowing or blanching of plant parts that are normally green.