The use of potassium phosphonate to control Phytophthora cinnamomi in native vegetation at Anglesea, Victoria

Field and laboratory experiments were used to determine the effectiveness of potassium phosphonate for control of Phytophthora cinnamomi in native plants. Potassium phosphonate (from phosphonic acid neutralised with potassium hydroxide) was hand-sprayed on native vegetation in field sites at Anglesea, Victoria. Potassium phosphonate concentrations of 6 g a.i./L controlled disease progress in plants of Xanthorrhoea australis that exhibited the initial decline stages of infection. Plants that showed severe disease symptoms including brown foliage died irrespective of potassium phosphonate treatment. Phytotoxicity occurred in 9 out of 36 plant species at a concentration of 6 g a.i./L potassium phosphonate. Species most severely affected by potassium phosphonate were Banksia marginata and Eucalyptus willisii. Closed environment experiments on four species showed phytotoxicity to seedlings of E. willisii and Leptospermum myrsinoides. Laboratory analyses of isolates of P. cinnamomi from the field sites showed inhibition of hyphal growth at potassium phosphonate concentrations ≥ 1 g a.i./L. When used at appropriate concentrations, potassium phosphonate has potential to control P. cinnamomi in the types of heathland and forest communities studied.