Tree disease theory

Press, 2 June 1981, Page 25

Tree disease theory

PA Rotorua Rotorua Forest Research Institute pathologists are now almost certain that the pine forest disorder in Northland has been caused by fungi. The head of the institute s research team, Dr G. B. Sweet, said it was difficult to prove this theory, but tests were now under way and results should be available late this month. Dr Sweet said it was usual for pine needles on the lower parts of a tree to die through lack of.sunlight and be attacked by fungi. In the Northland trees, however, the pathologists believe peculiar weather conditions have encouraged the fungi to at-

tack the healthy needles higher on the tree. “We think the humid and warm conditions throughout the summer have allowed the fungi to attack the healthy needles instead of only the dying needles usually affected,” he said. A far greater amount of fungi was found on the trees in question than would have been normally expected. “The probability that this is the cause is high. We are attempting to simulate the weather conditions in the F.R.I. artificial climate rooms to demonstrate this theory.” Two other less likely theories are also being considered by the investigating

team. The first is that some sort of pollution has damaged the trees. “We have followed this theory right through and are unable to tie it to any known pollutant. There are still two analyses to come in. but this theory is unlikely,” Dr Sweet said. The second is that some unknown disease has caused the disorder. “That is the one we have obviously given most attention. We' have made all the pathological tests and can find no evidence to support this. We still cannot totally discount it but I would put it at less than a 1 per cent chance,” Dr Sweet said.