New Zealand Journal of Forestry (1993) 38(2): 21–24
©New Zealand Institute of Forestry
Cyclaneusma needle-cast and Dothistroma needle blight in NZ pine plantations
Cyclaneusma minus (Butin) DiCosmo et al. and Dothistroma pini Hulbary both cause severe defoliation of pine trees on some sites. Cyclaneusma affects one-year-old foliage, is most severe after a mild wet winter, and is most common on 11- to 20-year-old trees; whereas Dothistroma affects current foliage, is most severe after a wet summer, and trees are usually resistant after about 15 years. Trees with average Cyclaneusma disease levels of 80% showed a reduction in volume increment of 60%; and if 50% of final-crop trees are affected by the disease, losses of 71m3/ha and $3200/ha in net revenue were predicted at the end of the rotation. A Dothistroma infection level of 50% over several seasons would result in a 50% reduction in volume increment. Cyclaneusma may have a more significant effect on stand growth than Dothistroma because it affects trees from six to 20 years old, whereas Dothistroma affects trees from planting to 15 years old, thereby creating the opportunity to cull highly susceptible, stunted trees during the first and second thinning operations.
At high-risk sites, Cyclaneusma can be controlled by selecting susceptible trees and culling them during the first and second thinning operations. Aerial applications of copper fungicide to control Dothistroma were effective in unpruned, highly stocked stands; growth response to spraying was difficult to repeat in stands which had been pruned and thinned regularly.