Stone fruit tree deaths ‘no mystery’

Press, 9 December 1983, Page 23

Stone fruit tree deaths ‘no mystery’

Recent tree deaths in Central Otago were not the result of a mystery disease, the M.A.F. has announced.

According to the senior advisory officer in Alexandra, Mr John Kelly, the major factors involved in the tree deaths were tree nutrition, soil management, drainage, cold hardiness and disease, particularly bacterial blast. “Because of concern within the stonefruit industry implicating an unknown mystery disease in recent tree health problems, M.A.F. and D.S.I.R. Soil Bureau staff met recently to review and report on the situation,” Mr Kelly said. “The first task the group undertook was to review the history of the development of the disorder over the past two seasons. During this time, many trees have been affected and several

avenues of investigation have been followed.” Information on soil management factors that could be involved, particularly low pH levels that were found below many affected trees in 1982, was presented to the group. “Aluminium toxicity could be one result of low pH levels,” Mr Kelly said. “Other factors discussed covered tree nutrition particularly late and/or excess applications of nitrogen. “Soil water, drainage and other tree management practices influencing ‘cold hardiness’ of trees, and the influence of unusual climatic conditions and how all these factors are capable of predisposing trees to bacterial blast invasion, were also discussed,” he said. The group made proposals for further study of the problem. It also plans to publish a guideline for

orchardists outlining practices designed to minimise the susceptibility of trees to the disorder. It is planned to have this distributed before Christmas. Trials have commenced looking at liming requirements and the effects of various types and rates of fertilisers on soil chemistry and tree growth. Work on the effect of low pH and high aluminium levels on tree health are continuing.

Microscopic examination to determine the degree of cell injury due to low temperatures are being undertaken by M.A.F.’s Plant Health Diagnostic Laboratory at Lincoln. “Hopefully a similar combination of circumstances won’t occur again next year and hence the disorder will not be as widespread,” Mr Kelly concluded.