Abstract
A field trial was designed to determine whether the control of pests and pathogens by regular chemical treatments could increase volume in E. globulus plantations. There were four foliar treatments, fungicide, fungicide plus insecticide, insecticide and control. The treatment plots were separated by buffer zones. The trial involved two plantations (Bill’s and Sixpenny) over four years. A total of 500 trees were used for each treatment (n= 2000). The incidences of pests and diseases were similar between plantations over the four years of the trial. Standardised tree volumes were higher at Bill’s than at Sixpenny in each year and the rate of increase between years was also greater at Bill’s. The differences in tree volume caused by treatment by 2004 were comparatively minor, but still significant. Post hoc LSD tests showed that at Bill’s standardised tree volumes were greater when both insecticide and fungicide were added. At Sixpenny, the greatest improvements occurred with the use of insecticide alone. The improvements in volume as a result of insecticide or fungicide treatment ranged from up to 8.6% (Bill’s) to up to 13% (Sixpenny). As the increase in yields was minimal, they represented very little benefit compared to the cost of applying the treatments on a regular basis. The differences between plantations were most likely due to soil type and climate. If disease and pest incidence had been higher, chemical treatments may have been cost effective.