Inhibition of Phytophthora cinnamomi mycelial growth with stabilised hydrogen peroxide

The efficacy of hydrogen peroxide (H₂O₂) was evaluated for the inhibition of mycelial growth of Phytophthora cinnamomi in vitro. Phytophthora cinnamomi infects many crops globally causing root, collar and crown rot, resulting in significant economic losses for producers. Two 30% (w/v) H₂O₂ products, each stabilised with a different concentration of 1-hydroxyethylidene-1, 1-diphosphonic acid (HEDP) (3% versus 0.003% w/v) were compared to determine the most efficacious H₂O₂ concentration as well as potential interactive effects of the stabilising compound. Inhibition of P. cinnamomi growth was evaluated by amending potato dextrose agar media (PDA) with a range of concentrations of the test solutions. The biocidal activity of H₂O₂ was enhanced by a higher concentration of HEDP. Concentrations from 6.25 mL/L of the H₂O₂ product with 3% HEDP provided 100% inhibition of mycelial growth in vitro. Neither the product with 0.003% HEDP, nor HEDP stabiliser without H₂O_2, achieved comparable inhibition. Our results highlight an opportunity to expand the use of stabilised H₂O₂ products developed for cleaning of drip irrigation emitters to include the control of Phytophthora spp. and potentially other waterborne plant pathogens.