Evaluation of vetiver grass root growth, oil distribution, and repellency against formosan subterranean termites

The growth rate of vetiver grass [Vetiveria zizanioides (L.) Nash (Graminales: Poaceae)], roots, and oil distribution were evaluated in an 8-month field study. The amount of vetiver oil present in the root system increased with each sampling date. In December, the final sampling period, mean root weight increased 520% from the previous sampling period (October). At the end of the study, root growth measured over 2 m long and 25 cm wide and weighed 0.48 kg (dry weight). In addition, a laboratory study was conducted to determine if the roots of vetiver grass when used as mulch, are effective against Formosan subterranean termites, Coptotermes formosanus Shiraki (Isoptera: Rhinotermitidae). In past studies, chemical components in the roots of this grass were shown to be effective repellents and toxicants to Formosan subterranean termites. In the present study, the 25% vetiver root mulch treatment proved to decrease tunneling activity and wood consumption and increase termite mortality. These results provide preliminary evidence that vetiver roots may have use as an additive to garden mulches against termites.