Synthetic herbicides were more effective than a bioherbicide based on Chondrostereum purpureum in reducing resprouting of Rhododendron ponticum, a host of Phytophthora ramorum in the UK

Abstract

A UKfieldtrialcomparedtheefficacyofarangeof synthetic herbicidesand thefungal biocontrolagent Chondrostereum purpureum (Pers.) Pouzar at preventing resprouting of Rhododendron ponticum L. following cutting, and hence countering infection with Phytophthora ramorum Werres or P. kernoviae Brasier. Treatments were applied tocutrhododendronstumpsinthesummerandwinter,andregrowthwasevaluated25monthsafterapplication. Allchemicalherbicidetreatmentssignificantlyreducedregrowth,andwouldthereforehelptolowerreinfectionby P. ramorumor P. kernoviae.Timingofapplications(summerorwinter)didnotaffectefficacy.Picloramwastheleast effectiveof thechemical herbicide treatments. A 20 percentsolution of RoundupProBiactive w (360 g l 21 glyphosate;Monsanto)appliedtostumpsimmediatelyaftercuttingwasaneffective,low-toxicityandinexpensivemeans of preventing regrowth, although some follow-up treatment was necessary. If approvals for glyphosate formulationswerelostinthefuture,productsbasedontriclopyrorpicloramcouldbepotentialsubstitutes.Useofthewoodrottingbasidiomycete C. purpureumasabiocontrolagentdidnothaveastatisticallysignificanteffectinthisstudy, althoughthepossibilityofasynergisticeffectwithglyphosatehasnotbeenruledout.Itispossiblethatanyimpact of the biological agent becomes apparent only over a longer time frame and thus extended assessment periods wouldberequired.Refinementoftheapplicationtechniqueand/ortheformulationmethodaswellasamorecomprehensive strain selection might result in improved efficacy of the biocontrol treatment.