EFFECTS OF FERTILIZATION WITH AMMONIUM-SULFATE AND POTASSIUM-SULFATE ON THE DEVELOPMENT OF SPHAEROPSIS-SAPINEA IN CORSICAN PINE

Potted plants of Pinus nigra subsp. laricio were fertilized with ammonium sulphate (AS) and potassium sulphate (PS) each year during 3 consecutive years. The then 5-year-old plants were artificially inoculated with Sphaeropsis sapinea. The fungus caused much bigger bark necroses in plants that had been fertilized with AS, than in plants fertilized with PS. It is concluded that P. nigra growing in poor sandy soil becomes more susceptible to S. sapinea when fertilized with an excess of AS. This may explain partly the increased incidence of S. sapinea in P. nigra stands in areas with a high rate of atmospheric NH4-deposition in the Netherlands.