Controlling internal decay of preservative-treated utility poles
Giron, M.Y.; San Pablo, M.R.; Morrel, J.J.
FPRDI Journal 22(2): 39-48
Two methods of controlling internal decay in preservative-treated, standing utility poles were evaluated: application of fumigants and bandage wrap + vapam [metam]. To determine the retreatment cycle, core samples were extracted at yearly intervals over 4 years. These were bioassayed through the closed tube technique using Fomes lividus as the test decay fungus. Decay fungi were observed on 50% of the standing preservative-treated poles that had been in service for 10 years in Metro Manila. Poria sp. was isolated from most of the poles with internal decay and was found to cause considerable weight loss in apitong (Dipterocarpus grandiflorus), red lauan (Shorea negrosensis), white lauan (Shorea contorta) and tangile [Shorea polysperma]. Penicillium sp., Aspergillus niger, Trichoderma viride, Alternaria sp. and Curvularia inaequalis comprised 45% of the isolates. The population of decay fungi was observed to be very frequent at the groundline but decreased toward the poles' top. The efficacy of creosote, sodium pentachlorophenate (NaPCP), vapam, vorlex and methylisothiocyanate (MITC) and chloropicrin varied. However, complete inhibition of fungal growth was noted in test blocks when chloropicrin and MITC were applied at 125 micro g/cc and 50 micro g/cc, respectively, per wood block. Field tests revealed that vapam and MITC persisted for 3 years as shown by the inhibition of growth of F. lividus fungus in the bioassay tubes. Bandaging and the application of vapam or MITC markedly reduced growth of the fungus.