Forest efficacy trials on phosphite for control of kauri dieback

Abstract

In 2012, trials were established in four kauri forest sites severely affected by kauri dieback (Phytophthora agathidicida = P. taxon Agathis, PTA) to determine the potential of phosphorous acid (phosphite) as a control tool. Baseline assessments of 162 trial trees included canopy disease rating, trunk lesion dimensions and lesion activity (recent bleeding/ oozing). Phosphite (Agrifos®600) at concentrations of 7.5% or 20% was injected (20 ml) at 20-cm intervals around the trunk. Control trees were left untreated. After 1 year, half the previously injected trees were re-injected, in all cases with 7.5% phosphite. Phytotoxicity symptoms (leaf yellowing, browning or leaf/twig abscission) were noted in some phosphiteinjected trees, particularly where the 20% concentration was used. After 3 years, many more trunk lesions remained active (expressing ooze, continued expansion) in untreated trees (58.5%) than in phosphite-treated trees (0.8%). Average lesion expansion after 3 years was 12.7 cm in untreated and 0.4 cm in phosphite-treated trees.

High-Throughput Chemical Screening Identifies Compounds that Inhibit Different Stages of the Phytophthora agathidicida and Phytophthora cinnamomi Life Cycles

“…As this species is an emerging pathogen that was only formally described in 2015 ( Weir et al, 2015 ), comparatively little research has been carried out on treatment options. To date, phosphorous acid (phosphite) is the only chemical that has been used on kauri trees affected by P. agathidicida , and while this has proved an effective treatment, some signs of phytotoxicity were present at higher treatment concentrations ( Horner and Hough, 2013 ; Horner et al, 2015 ). The EC 50 for mycelial growth inhibition by phosphite was 4 μg/ml ( Horner and Hough, 2013 ), similar to the EC 50 we measured for benzethonium chloride (3.2 μg/ml).…”

“…Kauri dieback was first recognized over 40 years ago ( Gadgil, 1974 ) and is continuing to spread through the forests of northern New Zealand, rapidly killing trees of all ages and sizes ( Beever et al, 2009 ). Currently, there are no established treatment or control options for P. agathidicida , although the use of phosphite as a potential treatment for infected trees is being explored ( Horner and Hough, 2013 ; Horner et al, 2015 ).…”

Phytophthora agathidicida: research progress, cultural perspectives and knowledge gaps in the control and management of kauri dieback in New Zealand

“…Trials on diseased kauri trees showed dramatic healing of P. agathidicida ‐induced lesions following trunk injection with 7.5–20% phosphite (Horner & Hough, ; Horner et al , ), whereas lesions on untreated trees continued growing (Fig. e,f).…”

Management Strategies for Conservation of Tanoak in California Forests Threatened by Sudden Oak Death: A Disease-Community Feedback Modelling Approach

“…Secondly, in comparison with vegetation removal or thinning, chemical protection of tanoak with Agri-fos ® incurs considerably greater economic costs [43] and social and legal constraints to its implementation [38] (Q2c,d). While this and similar chemicals can be efficacious in preventing infection or disease from a range of Phytophthora [54], much remains unclear about their mode of action, interaction with the host genotype, and overall efficacy. A cost-effective coverage of chemical protection within stands is likely to be restricted by individual variation in treatment efficacy and variation in treatment costs.…”

“…These expectations are testable against field experiments and highlight influential parameter uncertainties, and, therefore, offer insights that could inform future research and practice of tree disease management and conservation. Our results are aimed at informing the management of P. ramorum in the Western USA, but could be leveraged to inform affected or at-risk areas in Western Europe and Eastern USA, and chemical protection strategies for other emerging Phytophthora worldwide [19,24,40,54]. Of course, an extension of this modelling effort, or similar de novo efforts require a careful examination of assumptions, and likely changes to those dictating dispersal, efficacy, and species-level infection and mortality dynamics.…”