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.

This in vitro study aimed at estimating the disappearance rates of 14 terpenes and terpenoids after 24-h incubation with mixed bacteria from caprine rumens. These compounds comprised nine monoterpene hydrocarbons (δ-3-carene, p-cymene, β-myrcene, (E)- and (Z)-β-ocimene, α-phellandrene, α-terpinene, γ-terpinene and α-terpinolene), four oxygenated monoterpenes ((E)- and (Z)-linalool oxide, 4-terpinenol, α + γ terpineol) and one sesquiterpene hydrocarbon (β-cedrene). They were individually exposed to goat rumen microflora for 24 h in 70 ml culture tubes at an input level of 0.5 ml/l. Terpenoids were the least degraded, 100% of (E)-linalool oxide, 95% of (Z)-linalool oxide, 91% of 4-terpinenol and 75% of terpineol remained intact after 24-h incubation. In contrast, α-terpinolene concentration in fermentation broth extracts was below quantification limit, thus indicating an extensive, if not complete, degradation by rumen bacteria. Only 2% of the initial amounts of α-phellandrene were recovered. The other monoterpenes and β-cedrene were partly degraded, with losses ranging from 67% for δ-3-carene to 90% for (E)-β-ocimene. The corresponding rates of disappearance were between 2.67 and 4.08 μmol/ml inoculum per day.