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 rad iata, Banksia integrifolia and Isopogon cuneatus. Foliar sprays of potassiu m phosphonate (0.1 g a.i./L or 1.0 g a.i./L) and Bion 500 WG (500 g/kg acib enzolar-S-methyl; 1.0 mu g a.i./L or 2.5 mu g a.i./L), separately and in co mbinations, were applied to these plants immediately after transplanting in to 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 incide nce of root infection, but no treatment eradicated the pathogen from roots or soil. Phytotoxicity was not observed in any treatment, demonstrating tha t effective control of Phytophthora root rot can be achieved on phosphorus- sensitive plants using low rates of phosphonate in combination with Bion.