Towards integrated pest management of phythophagous insects in Tasmanian blackwood (Acacia melanoxylon) plantations in New Zealand

Acacia melanoxylon provenance trials were assessed to investigate: (1) The degree to which insect populations influence growth and the change from juvenile to mature foliage. (2) How tree growth rates and overall performance respond to a range of fertiliser and planting regimes (V-bladed, line cut and planting on retired agricultural land). (3) How Acizzia acaciae, A. uncatoides and Acrocercops alysidota populations are influenced by a range of provenances and clones, under a range of fertiliser, and planting regimes. In a field trial, trees sprayed with the insecticide deltamethrin had significantly higher growth rates than unprotected trees infested with A. acaciae and A. uncatoides. The leaf miner A. alysidota did not cause leaf abscission but influenced tree development through shoot abscission, which led to multi-leadering. Insect infestation did not affect the rate of mature foliage (phyllode) development; the latter is more likely to be determined by genetic and environmental conditions. In field trials, trees from the Smithton, and Leven (Tasmania) and Jeerlang (Victoria, Australia) provenances had the highest growth rates compared with trees of other origins. In nutrient-deficient soils, addition of superphosphate (calcium and phosphorous) significantly improved growth rates (43%) and foliar nutrient levels. However, in fertile soils, fertilisers were associated with growth reductions (35%) and lowering of foliar nutrient levels. This suggests that in fertile soils fertilisers may have disrupted Rhizobium activity. In 7 - 19 year old West Coast forest plantations, foliar Ca, K, Mg and B concentrations were higher than those in fertilised 3 - 4 year old trees, which suggested that tree age had a major influence on foliar nutrition. Foliar nutrient levels for trees in line cut and V-bladed regimes were higher than those for trees in line dozed regimes. This appears to be a reflection of soil disturbance during site preparation. The overall development of trees was significantly better in the line cut regime, compared with trees in the other regimes, irrespective of stand age. This is because insect populations were below damage thresholds only in the line cut regime. In the field, psyllid and leaf miner populations varied significantly between provenances and trees receiving different fertilisers. Different foliar nutrients had varied effects on insect populations. Foliar calcium levels in trees growing in nutrient deficient soils reduced leaf miner populations. Perhaps calcium (such as calcium oxalate crystals) in the leaf structure physically influenced leaf miner survival; this needs to be substantiated. In the laboratory, A. uncatoides nymph development rates were significantly influenced only by different clones. On fertilised plants there was a significant reduction in nymph development time and an improvement in nymph survival. The level insect damage incurred by A. melanoxylon can be significantly reduced if trees are established in a line cut site or under a timber 'nurse crop' through to harvest. Providing trees are form pruned, then trees from the Smithton, Leven, and Jeerlang provenances will give good growth rates. In nutrient deficient soils, trees should be fertilised only with 200 g of superphosphate per plant at establishment. If these criteria are met, then it will be possible to successfully grow A. melanoxylon through to rotation