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/ 20cm intervals around the trunk Control trees were left untreated After 1 year half the previously injected trees were reinjected in all cases with 75 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 (585) than in phosphitetreated trees (08) Average lesion expansion after 3 years was 127 cm in untreated and 04 cm in phosphitetreated trees