Pruning and cypress canker in New Zealand

Abstract

In New Zealand, the planting of cypresses is hindered by cypress canker disease caused by Seiridium cardinale (W.W. Wagener) B. Sutton & I.A.S. Gibson and S. cupressi (Guba) Boesew.). Pruning is widely practiced in established plantations to improve timber quality, although knowledge of its effect on disease incidence remains imperfect. Stubs of freshly cut branches on 275 trees of Cupressus macrocarpa Gordon & Leyland were inoculated with an isolate of either S. cardinale or S. cupressi to investigate the potential for pruning wounds to act as infection courts. In total, 75% of stubs inoculated at the edge, and 60% of those inoculated at the centre, became infected and produced stem cankers after 1 year, whereas cankers were formed on only 2% of non-inoculated control stubs. Incidence of cankers differed significantly between isolates. A second experiment was conducted at the same site 2 years later when stand infestation had increased, this time without inoculating but instead relying on ambient field inoculum. Stem cankers were produced on 11% of stubs on 162 trees, as a result of natural infection following pruning during periods of light rain in spring and summer. This investigation confirmed the ability of Seiridium species to invade through fresh pruning wounds on C. macrocarpa, and strengthens the recommendation to remove diseased plant material early, to maintain a low level of natural-spore inoculum within stands. It also indicates that pruning during wet weather should be avoided. Cleaning or disinfecting implements among trees may also be appropriate when conducting silvicultural operations in diseased plantations.