Phosphorous acid for controlling <i>Phytophthora</i> taxon Agathis in kauri glasshouse trials

Abstract

Phytophthora taxon Agathis (PTA) is a serious problem in Auckland and Northland kauri forests Phosphorous acid (phosphite) is a potential treatment for infected or threatened trees In vitro tests on phosphiteamended agar showed that PTA was more sensitive to phosphite than other Phytophthora species commonly controlled by this chemical Before progressing to forest trials phosphite efficacy was tested on PTAinoculated kauri seedlings in the glasshouse Twoyearold kauri seedlings were inoculated with PTA applied directly to trunk wounds or by soil application Phosphite was applied as a foliar spray as a trunk injection or as a soil drench either 5 days before or 5 days after inoculation All untreated control trees died whether trunk or soilinoculated With phosphite injection survival was 100 following PTA soil inoculation and 67 following trunk inoculation Foliar spray and soil drenchapplied phosphite treatments were less effective than trunk injection although some trees survived