Stimulant levels to be used with two Low Intensity Harvesting (LIH) systems of Rubber under wet and intermediate zones of Sri Lanka

W.R.A.C. Prasanna1, V.H.L. Rodrigo2, D.C. Abeysinghe 1 and K.V.V.S. Kudaligama2
1Department of Plantation Management, Wayamba University, Sri Lanka
2Biochemistry and Physiology Department, Rubber Research Institute of Sri Lanka, Agalawatta, Sri Lanka

Harvesting latex from rubber trees (Hevea brasiliensis) is rather labour consuming and hence is the most costly operation contributing to 1/3 of the cost of production in rubber plantations. Further, it requires high level of skill which plays a part in the shortage of latex harvesters. Harvesting of latex is undertaken through the systematic wounding in the bark of the trunk. In Sri Lanka, two harvesting systems are widely used in base panel tapping, i.e., a half of trunk circumference tapped once in two (S/2 d2) and three (S/2 d3) days.

With the reduction of harvesting frequency, labour use in harvesting hence the cost decreases. However, yield stimulants (viz. Ethephon) are to be applied to increase the  yield on harvesting days as a compromise for the yield reduction due to less number of harvesting days in low frequency harvesting (LFH). In order to address labour issues, a system of harvesting the tree once in four days (S/2 d4) has recently been introduced and a weekly harvesting system (S/2 d7) is presently under investigation. In S/2 d4 and S/2 d7, the required doze of Ehephon has exactly not known and that would vary with the climatic condition. Therefore, the present study was aimed to identify the suitable concentrations of Ehephone required for S/2 d4 and S/2 d7 systems under two climatic regions, wet and intermediate zones of Sri Lanka.

Ethephon was applied in four concentrations (i.e. 2%, 3%, 4% and 5%) in the genotype RRIC 121 planted in both climatic zones. Yield performance in each system was evaluated against that of the traditional harvesting systems of S/2 d2 of which no stimulation was done. In the Intermediate zone, the S/2 d4 and S/2 d7 systems showed a yield increase of 7 and 14 grams per harvest per 1% increase in Ethephon concentration, respectively.  In the Wet zone, respective increases were recorded as 4 and 7 grams. The S/2 d4 system required ca. 3.7% and 3.3% concentrations of Ethephon in the Intermediate and Wet zones, respectively, to achieve the yields given by S/2 d2 system. In S/2 d7, Ethephon concentration of 5% was sufficient for both zones. The study also revealed that the range tested in Ethphone concentrations had no adverse effect on tree health as indicated by the percentage dry rubber content in latex. However, long-term studies at commercial scale together with financial analyses are required before coming to firm conclusions.