STIMULANT LEVELS TO BE USED WITH TWO LOW INTENSITY HARVESTING (LIH) SYSTEMS OF RUBBER UNDER WET AND INTERMEDIATE ZONES OF SRI LANKA

Abstract

Low frequency harvesting (LFH) systems of rubber (Hevea brasiliensis) result in reduction in labour use and cost. However, yield stimulants (viz. Ethephon) are to be applied to enhance the yield in each harvest as a compromise for the yield reduction due to less number of harvesting days. 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 Ethephon has exactly not known and that would vary with the climatic condition. Therefore, the present study was aimed to identify the suitable concentrations of Ethephon 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%) and yield performance in each system was evaluated against that of the traditional harvesting systems of S/2 d2 (tapping the tree once in two days). In the Intermediate zone, 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 3.2 % concentrations of Ethephon in the Intermediate and Wet zones, respectively, to achieve the yields given by S/2 d2 system. In S/2 d7, 5% Ethephon was sufficient for both zones. Ethephon concentrations tested had no adverse effects on tree health. Needs for commercial scale studies with financial analyses are discussed.