Protective Measures

Decay and biodeterioration of bamboo culms during outdoor storage can be checked to a great extent by adopting good storage yard management practices. Culms should be stacked horizontally over raised walls to facilitate water drainage and air circulation. For reed bamboos, vertical stacking results in a small gain in pulp yield over horizontal stacking because the former suffers less fungal damage.

Recently, an exhaustive review on bamboo preservation techniques has been made by Kumar et al. (1994) on behalf of INBAR. Basically, there arc two methods for increasing the durability of bamboo: (1) non-chemical method, in which preservatives are not involved; and (2) chemical method.

Bamboos used for structural purposes are often treated by non-chemical or traditional method, although not much is known about their real effectiveness. However, the treatment cost is almost nothing and can be carried out at village level without any special equipment. These methods include curing, smoking, lime-washing and soaking. (Martawidjaja 1986; Singh and Nigam 1968; Sulthoni 1987; Kumar et al. 1980, 1983; Liese 1993; Gnanaharan et al. 1993). Bamboo culms are treated during or immediately after extraction and before stacking in the storage yard. Curing involves leaving harvested culms, with branches and leaves intact, in open air. The leaves continue to transpire causing the starch content of the culms to fail. The second traditional method is to smoke bamboo culm over fire. This is considered an effective treatment against insects and fungi. Painting of culm with lime is widely used and said to ward off fungal attack. Often, culms are painted with a mixture of tar and sand, or plaster, cow dung and lime, to prevent fungal and insect attacks. Another method is to submerge the culms in either stagnant or running water, or mud for several weeks.

Chemical protection ensures a longer life for bamboos. Culms can be treated using a variety of chemicals, depending upon the culm condition- green or dry - and also on the end use of bamboo. Various chemical treatments recommended for increasing the service life of fresh (green) bamboo, include : steeping, sap displacement, diffusion process and boucherie process. Treatments for dry bamboo culms include soaking in a preservative solution, hot-cold process and pressure treatment.

Methods that use preservative chemicals are generally more effective than non-chemical methods in the protection of bamboo under storage, but they are not always economical or feasible. Recently, Gnanaharan et al. (1993) suggested a low-cost treatment for reed bamboos against biodeterioration. Reed bamboos used for mat weaving can be stored effectively even up to 8 months by keeping them under water (running or stagnant), or a disinfectant solution (bleaching powder or potassium permanganate) or preservative chemical solution (copper sulphate or boric acid) of very low concentration. Chemical treatment on a large scale is performed mainly in India, Japan and Taiwan-China.In Japan, prophylactic treatment and surface protection during processing is common. Brushing and spraying of bamboos are rarely carried out except for prophylactic purpose. However, these methods have only a temporary effect because of the very low penetration of the preservatives.

Prophylactic chemical treatment at the time of stacking and after 4-6 months is recommended for protecting structural bamboo culms stored outdoors (Kumar et al. 1990, 1994). For long-term storage of pulp bamboos in the open, chemical treatment (spraying) during different stages of stack forming --at 3, 4, 5 and 6 m heights--and covering with treated bamboo mats or thatch grass are recommended. Preservative chemicals recommended for treatment of bamboo include:

1 Coal tar creosote and fuel oil (50:50) by weight. In high termite-infested areas, it is preferable to add 1% dieldrin. Coal tar creosote should meet the relevant standard specification for preservation purposes (Anonymous 1961);

2 Copper-chrome-arsenic composition containing copper sulphate, sodium or potassium dichromate and arsenic pentoxide in the proportion of 3:4:1 (Anonymous 198lb);

3 Borated-copper-chrome-arsenic (SBOR) composition conforming to the composition (patent pending) prescribed by the Forest Research Institute, Dehra Dun, India;

4 Acid-copper-chrome composition containing copper sulphate 50 parts, sodium dichromate 47.5 parts, chromic acid 1.68 parts (equivalent to 2.5 parts of sodium dichromate) (Anonymous 1981a);

5 Copper-chrome-boron composition containing boric acid, copper sulphate and sodium or potassium dichromate in the proportion of 1.5:3:4 (Anonymous 198lc);

6 Ammoniacal copper-arsenite composition containing copper-sulphate, arsenic trioxide dissolved in ammonia (Dev et al. 1991);

7 Boric acid: borax in 1:1.54 proportion;

8 Copper naphthenate/abietate and zinc naphthenate/abietate containing 0.5% copper or l% zinc;

9 Sodium pentachlorophenate, boric acid and borax in 5:1:1 proportion (2.5% solution) for prophylactic treatment;

10 Copper-chrome-arsenic composition, containing copper sulphate, sodium or potassium dichromate, and sodium pentachlorophenate in 2:O.5 proportion (2.5% solution) for prophylactic treatment; and

11 DP (2, 5-chloro-3-bromophenol) 0.l% solution for prophylactic treatment (Ma 1990).

Chemical preservatives recommended against fungal and insect attacks are invariably toxic to mammals. Slight carelessness in the use of such chemicals can endanger the safety of those handling the chemicals and freshly treated bamboos. Although the chemical preservatives recommended for bamboos have long safety records, many of them are still under constant scrutiny and a few are banned in some countries.