Germination experiments were conducted in petri dishes to test the effect of vetiver oil and one of its minor components, nootkatone, on six common weed species. Vetiver oil inhibited germination of redroot pigweed, common lambsquarters, giant ragweed, pitted morningglory, and velvetleaf. Nootkatone, at much higher concentrations than it occurs in the oil, exhibited germination inhibition for all weed species except velvetleaf. Redroot pigweed was the most sensitive species with germination inhibition at 0.1 to 1.0 mg/ml of vetiver oil and nootkatone. At 1.0 to 8.0 mg/ml, nootkatone reduced germination of giant ragweed by 24 to 92%, whereas vetiver oil reduced the germination only by 6 to 11%. Vetiver oil and nootkatone also inhibited seedling expansion of redroot pigweed and common lambsquarters. No significant inhibition of germination and seedling expansion was found for sicklepod. These laboratory studies provide preliminary evidence that nootkatone and vetiver oil may have use as herbicides.
Nomenclature: Nootkatone, 5,6 dimethyl-8-isopropenylbicyclo[4.4.0]dec-1-en-3-one; common lambsquarters, Chenopodium album L. #3 CHEAL; giant ragweed, Ambrosia trifida L. # AMBTR; pitted morningglory, Ipomoea lacunosa L. # IPOLA; redroot pigweed, Amaranthus retroflexus L. # AMARE; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby # CASOB; velvetleaf, Abutilon theophrasti Medicus # ABUTH.
Additional index words: Amaranthus retroflexus, Ambrosia trifida, Chenopodium album, essential oil, herbicidal activity, sesquiterpene.
Abbreviations: I50, concentration required to inhibit 50% of seed germination.