A look-see at Vetiver Grass in Malaysia

2.3. USE OF SELECTIVE HERBICIDES TO MAINTAIN QUALITY VETIVER HEDGEROWS

Weed management is an important aspect in the maintenance of quality Vetiver hedgerows. In Malaysia, weeds grow luxuriantly under high rainfall (2100 – 2500mm/year), humidity (52-96%) and temperature (21-35^oC). These weeds compete with the Vetiver directly for nutrients, water and light. The last factor is most important, as Vetiver is not shade tolerant. As a result of strong competition caused by swarming over and shading by these weeds, the growth of Vetiver hedgerow is retarded and suppressed. In a severe weed-infested situation, even an established Vetiver hedgerow will be weakened and less effective for its intended purpose.

Weed is a plant growing where it is not desired. In Vetiver hedgerow establishment and maintenance, the weeds are mainly grasses and broad-leaves. The grasses are less important. The more damaging weeds are broadleaf such as Asystasia intrusa, Chromolaena odorata (Siam weed), and Mikania micrantha (photos 14 to 17). Included also are the leguminous creepers normally grown as covers in agricultural plantations (Photos 18 and 19). These are the most noxious weeds because they swarm over, strangle and shade out the Vetiver hedgerows.

a) Control of Noxious Weeds in Vetiver Hedgerows

An evaluation of selective herbicides in the control of A. intrusa was conducted at the Rubber Research Institute Experiment Station, Sungai Buloh^*. The herbicides tested were Starane₂₀₀ 0.1 and 0.3 1/ha and 2,4-D amine 0.5 and 1.5 1/ha. The volume of spray was 450 1/ha (Photo 20). Examples of plots marked for testing and treatment arrangements are shown in Photos 21 and 22. Photos 23a to 23d traced the schedule of observations at 0, 1, 2, 4 weeks and its response to the 2,4-D amine 1.51/ha treatment.

At 7 days after spraying, the leaves of A. intrusa were scorched by Starane₂₀₀ (0.31/ha) and 2,4-D amine (0.5 and 1.51/ha) while light scorching was found in Starane₂₀₀ 0. 11/ha plots. At 14 days, 60% control was recorded for Starane₂₀₀ (0.31/ha) and 2,4-D amine (0.5 and 1.51/ha) while in Starane₂₀₀ (0.11/ha) plots, only the leaves were scorched but not the stems. The same trend was recorded at 28 days after treatment. At 45 days after treatment, the % control for Starane₂₀₀ (0.31/ha), 2,4-D amine (0.5 and 1.51/ha) was 93%, 92% and 98% respectively (Table 8). Poor control of 50% was recorded in Starane₂₀₀ 0. 11/ha plots and there was regeneration from the stems. Photos 24 and 25 records the other 2 effective herbicides of 2,4-D amine 0.51/ha and Starane₂₀₀ 0.31/ha at 4 weeks. Therefore, for control of A. intrusa the recommended herbicides spraying are 2,4-D amine at rates of 0.5 and 1.51/ha or Starane₂₀₀ at 0.3 1/ha.

Based on other ad hoc experiments in the establishment of Vetiver hedgerows, the various herbicides and rates recommended to control other weeds are as follows:

Chromolaena odorata
(Siam Weed) Ally 20 DF 150 g

2,4-D amine 1.5 l

Starane₂₀₀ 1.25 l

Mikania micrantha 2,4-D amine 1.0 l

Starane₂₀₀ 0.5 l

Pueraria phaseoloides
(Legume) Ally 20 DF 100 g

Starane₂₀₀ 0.375 l

TABLE 8 EFFECT OF HERBICIDES ON THE CONTROL OF ASYSTASIA INTRUSA IN VETIVER HEDGEROWS

Herbicides
Rates 1/ha
% control* (45 days after treatment)

Starane ₂₀₀
0.1
50

Starane ₂₀₀
0.3
93

2,4-D amine
0.5
92

2,4-D amine
1.5
98

*Mean of 3 replicates

(Courtesy: Chee Yan Kuan)

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