Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/1995
Publication Date: N/A
Interpretive Summary: Monoterpenes are a group of chemicals that are among the major odor and flavor constituents of plants and are used in large quantities in over-the-counter medications and perfumes. The commercial herbicide, cinmethylin, is a simple derivative of the common monoterpene 1,4-cineole. As part of a research effort to identify natural compounds which could be chemically modified to produce environmentally-friendly herbicides, we had previously identified five monoterpenes which strongly inhibited the germination of several problem weed species but exhibited low toxicity to corn and soybean. We synthesized numerous derivatives of these five monoterpenes and tested them for preemergent and postemergent herbicidal activity. Although none of the new compounds exhibited strong postemergence activity, several of them were highly herbicidal when applied preemergence. These results offer leads to further chemical modification of monoterpenes for use as herbicides.
Technical Abstract: The preemergence herbicide cinmethylin is a benzyl ether derivative of the monoterpene 1,4-cineole. Other oxygenated monoterpenes (carvone, citronellol, fenchone, geraniol and pulegone) were previously found to inhibit the germination and growth of several weed species while exhibiting low phytotoxicity to soybean. Benzyl ether derivatives of these oxygenated monoterpenes were synthesized and examined for preemergence and postemergence activity towards corn, soybean, wheat and velvetleaf. Benzyl pulegyl ether exhibited the most preemergence activity when applied directly to the soil, completely inhibiting wheat and velvetleaf emergence at 1.0 kg ha(-1) while significantly inhibiting soybean emergence. Several of the benzyl ethers were more inhibitory to velvetleaf radicle elongation relative to cinmethylin but less inhibitory to corn and wheat radicle elongation in petri dish bioassays. Several of the benzyl ethers exhibited some postemergence activity when applied at 1.0 kg ha -1 rates to seedlings of the test species 10 d after emergence.