Volatile Monoterpenes as Potential Parent Structures for New Herbicides

Eighteen volatile monoterpenes, which are among the major constituents of essential oils from plants, were screened for phytotoxicity to several crop and weed species. Several monoterpenes containing an oxygen function severely inhibited germination of four different annual weeds while concurrently displaying little effect on soybean germination. Soybeans varied in their sensitivity to various monoterpenes (measured by seedling growth), with a-terpineol and geraniol selectivity inhibiting weed seed germination while having little or no effect on soybeans. All of the monoterpenes tested exhibited relatively high germination and growth inhibition to corn and wheat. Nomenclature: Cinmethylin, exo-l-methyl4-(I-methylethyl)-2-[(2-methylphenyl)methoxy].7-oxabicy. clo [2.2.1] heptane; Italian ryegrass, Lolium multiflorum Lam. #3 LOLMU; large crabgrass, Digitaria sanguinalis (L.) Scop. #DIGSA; redroot pigweed, Amaranthus retroflexus L. #AMARE; velvetleaf, Abutilon theophrasti Medik. #ABUTH; alfalfa, Medicago sativa (L.) 'Vernal'; corn, Zea mays (L.) 'Pioneer 3377'; cucumber, Cucumis sativus (L.) 'Edmonson'; soybeans, Glycine rna;\: (L.) Merr. 'Williams 82'; wheat, Triticum aestivum (L.) 'Coker 68-19'. Additional index words: Allelochemicals, germination, growth inhibition.