Combinations of potassium phosphonate and Bion (acibenzolar-S-methyl) reduce root infection and dieback of Pinus radiata, Banksia integrifolia and Isopogon cuneatus caused by Phytophthora cinnamomi

Phytophthora cinnamomi infects the roots of and causes dieback of Pinus radiata, Banksia integrifolia and Isopogon cuneatus. Foliar sprays of potassium phosphonate (0.1 g a.i./L or 1.0 g a.i./L) and Bion 500 WG (500 g/kg acibenzolar-S-methyl; 1.0 mu g a.i./L or 2.5 mu g a.i./L), separately and in combinations, were applied to these plants immediately after transplanting into potting mix infested with P. cinnamomi. After 14 weeks the incidence of root infection by P. cinnamomi was assessed and plant growth measured. The incidence of root infection was reduced by sprays of potassium phosphonate or Bion. Combinations of phosphonate and Bion additively reduced the incidence of root infection, but no treatment eradicated the pathogen from roots or soil. Phytotoxicity was not observed in any treatment, demonstrating that effective control of Phytophthora root rot can be achieved on phosphorus-sensitive plants using low rates of phosphonate in combination with Bion.