This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

The research from this project indicated that the pecan borer and lucerne leafhopper were unlikely to have any significant impact on pecan production and were no longer considered significant pests to the pecan industry.

The findings from the research at the time indicated that borer infestations were not the direct cause of mechanical pruning (as previously thought), but were the result of dead or dying timber which was caused by lower limb shading. Lower limb death was caused directly by shading and was not caused by borers or mechanical pruning. Tree collapse was rare and was not caused by borers, but was caused by cutting trees open (with chainsaws to remove borers) and allowing the timber to die and become dry and brittle. Therefore, manual removal of borers from the trunk was likely to cause more damage to the trees than the presence of borers. As the borer was no longer considered a pest, manual removal and further control methods were no longer recommended. This significantly reduced input costs and increased profits to the pecan industry.

Cultural control practices through improved tree health were investigated. Primarily the limb dieback and borer problem was caused by: pruning lower limbs too short, pruning in a rectangular shaped hedge, growing hedges too tall for their row space and growing some hedges in an east-west direction. Recommended improved canopy management and pruning practices include: pruning hedges into a tapered shape (preserving the lower limbs as wide as possible), pruning in a North-South direction and limiting tree height. By producing a healthy more productive tree, not only did limb death and borer incidence decrease, but yield and nut quality increased, resulting in increased profits.

IPM options for controlling leafhoppers had been developed. By simply changing mowing practices (to mowing every alternate row, rather than mowing all rows simultaneously) leafhoppers could be reduced whilst beneficial organisms were preserved.

Through the success of this research, the Australian pecan industry had predominantly remained insecticide free, thus retaining a sustainable “clean” industry with significant domestic and export value.