The photodynamic herbicidal performance of δ-aminolevulinic acid in combination with four chlorophyll biosynthesis modulators was evaluated under greenhouse conditions, using corn, soybean, and ten weed species. Treatments resulted in accumulation of various amounts of protoporphyrin IX and of monovinyl and divinyl Mg-protoporphyrin IX and protochlorophyllide. Accumulation of these tetrapyrroles was accompanied by various degrees of photodynamic injury, depending on treatment, plant species, and somewhat the modulator. The lower photodynamic susceptibility of dark monovinyl/light monovinyl and dark divinyl/light divinyl plants toward the accumulation of monovinyl and divinyl protochlotophyllide, respectively, was attributed to their greater abilities to metabolize these protochlorophyllides in the light. On the other hand, the higher photodynamic susceptibility of the dark monovinyl/light divinyl weed species toward the accumulation of monovinyl protochlorophyllide was attributed to their lower ability to metabolize the accumulated monovinyl protochlorophyllide in the light.
