INFLUENCE OF SILVICULTURAL PRACTICES ON TWISTING RUST INFECTION AND DAMAGE IN MARITIME PINE, AS RELATED TO GROWTH

A three-year study was carried out on the influence of silvicultural i ntensification on infection and damage caused by Melampsora pinitorqua , the twisting rust fungus, in maritime pine, Pinus pinaster Air. The silvicultural practices studied were phosphorus fertilisation, the mod e of stand establishment (either seeds or plants), and pine density. G rowth and nutrition variables were also measured. Infection and damage were the most important in the first two years, which could reflect h igher resistance with aging. At the end of the experiment, when pines were 4 years old, the planted, fertilised pines turned out to be the m ost damaged and the tallest, while the sown, non-fertilised pines were the least damaged and the smallest. Final damage was mainly explained by the damage observed in the earlier years. Annual damage was signif icantly correlated with infection percentage, more closely in the firs t year of observation. Higher susceptibility of the planted pines was associated with better growth and was explained by a greater amount of susceptible tissues. Under our experimental conditions, this explanat ion could not be retained for the fertilisation effect. However, phosp horus fertilisation induced changes in the nutritional status of pines . A significant positive correlation was observed between the phosphor us and potassium content on one hand and the susceptibility and damage on the other hand. Density effects were seldom observed in the experi ment, either on growth or susceptibility variables. The positive relat ion between pine growth and rust damage, as confirmed in this study, e mphasises the need for an integrated management of intensively managed pine stands, taking into account the disease hazard. (C) 1997 Elsevie r Science B.V.