September 2004. Do the roots of Vetiver grass damage taro? This was asked by American Samoa in connection with using the grass in 10-20% slopes with a community where taro is important.
It was thought the report that they damaged taro came from an IBSRAM Sloping Land Project. Vetiver grass seems to grow best on dry soils, e.g., to stop erosion in sugarcane fields, but not in more swampy, low-lying, less-erodable soils, conditions which favor Colocasia taro. Members did report growing taro with well-established Vetiver grass, but had experienced no problems, although in one case there was a lot of damage due to Papuana beeltes. The taro had been heavily mulched with Vetiver grass prunings, and this no doubt provided breeding sites, in the same way as “soil under grass species which produce dense fibrous roots forming mats such as B. mutica, Saccharum spp., Phragmites sp. and P. conjugatum.” (Thistleton et al., (2003) PRAP unpublished report).
Notes on vetiver grasss can be found on Ecoport:
The Fiji Land Use Department has worked with Vetiver grass for a number of years now. A research plot of 10+ years exists in Waibau in the province of Naitasiri and there have never been any complaints from farmers of Vetiver grass piercing taro, rendering them inedible or non-marketable. However, it might happen if the taro are planted too close to the Vetiver grass hedges that are not well established and the roots are still finding their way down the soil layers. With an established vetiver hedgerow, roots are already down the soil profile, sometimes below 1m, thus, they will not be able to affect taro, the corms of which are, at most, 30 cm below the top soil.
It seems that roots of Vetiver grass are unlikely to pierce taro corms; however, young rhizomes of Imperata cylindrica(Kunai/Cogon grass) can pierce the underground parts of taro, sweet potato, yams and even bananas. And in Fiji, underground shoots of Nutgrass, Cyperus rotundus, are known to pierce ginger rhizomes, providing entry points for fungal and bacterial diseases, and lowering the yield of the crop.
Note, earlier messages talked about the use of Vetiver in Thailand, Northern Mariana Islands, Samoa, Solomon Islands, Papua New Guinea and Fiji. It was the post from Samoa that mentioned that runners can penetrate taro corms. The past work by the International Board for Soil Research and Management (IBSRAM) was noted in which a regional project in the Pacific explored ways of reducing soil erosion in sloping land agriculture – using locally appropriate technologies. Some of this work was taken up by the Pacific Regional Agricultural Programme (PRAP). The IBSRAM study identified 3 main reasons why Vetiver may not be acceptable to Pacific islanders: (1) concern about its invasive capability, (2) concerns that it may harbour pests & diseases, and (3) farmers not being able to see a direct (cash) benefit of growing the grass.
Apart from erosion control Vetiver can have various other uses, including use of leaves for thatch, mulch, making natural hedges and marking land boundries, and Vertiver oil production. In the highlands of Papua New Guinea, it is now being promoted for reducing erosion in very steep cultivated areas such as Simbu Province where 70% of the province lies between 1000-2600 m above sea level and 40% of the land has slopes greater than 20 degrees. Vetiver’s erect leaves make good thatch and is also seen as an alternative to Kunai grass (Imperata cylindrica), which has been replaced by the invasive, less useful grasses Pennisetum purpureum (Elephant grass) and Melinis minutiflora (May grass).