Abstract

Studies are reported on occurrence, symptoms and damage caused to the wood of teak (Tectona grandis) trees at several sites in Kerala (on different campuses of the Kerala Forest Research Institute), by water blisters. The problem was first reported as early as 1896; it is not widespread. Healthy looking trees, mostly along riversides, exude a straw coloured sap which leaves a black discoloration on their bark surface. Observations showed that the blister is restricted to the stem, and is always caused by a radial shake in the stem wood. Loss is serious in terms of log quality, resulting in rejection of affected timber for high quality veneer, boards, or turnery stock. The exudate has a similar chemical composition to xylem sap, but the concentration of inorganic salts and the pH were high. Exudation rates follow a diurnal rhythm similar to that root pressure. The flow continues throughout the year, with the volume of exudate depending on soil water availability. The occurrence of water blisters seems to be related to proximity to a river/canal. In a plantation at a site at Nilambur, occurrence was as high as 30 within 50 km of the river bank, but decreased steadily at greater distances, becoming was negligible at 350 m from the river