Submitted to: Encyclopedia of Agrochemicals
Publication Type: Book / Chapter
Publication Acceptance Date: February 5, 2002
Publication Date: January 15, 2003
Interpretive Summary: This is a book chapter.
Technical Abstract: Several chemical classes, including p-nitrodiphenyl ethers, phenylpyrazoles, N-phenylphthalimides, thiadiazoles, oxadiazoles, triazolinones, and oxazolidinediones, target the enzyme protoporphyrinogen oxidase (Protox) and numerous herbicides affecting this step in porphyrin synthesis have been commercialized. Most Protox inhibitors are used for post emergent weed management in soybean, though newer compounds have been developed to provide preemergent weed control or to be used in grain crops. The mechanism of action associated with inhibition of Protox is complex, involving the accumulation of the photodynamic chlorophyll precursor protoporphyrin IX (Proto) that causes rapid oxidative damage in tissues exposed to light. Crops tend to be tolerant to Protox inhibitors via rapid metabolic degradation and there is no known instance of naturally evolved resistance to these herbicides. These herbicides are considered enviornmentally safe and the newer products have been registered as reduced-risk herbicides under the new Food Quality Protection Act guidelines.