BBC Wildlife - UK (2020-08)

a furtherrustfungusfromtheKashmir

region,butthepoliticalsituationthere,not

tomentiontheCOVID-19pandemic,is

makingcollectionnighonimpossible.

Fornow,boththeIndianandPakistan

rustfungiareoutata totalof 36 sites–

withscientiststryingtomatcheachstrain

withitscorrespondingbiotype– andthe

resultshavebeenmoreencouraging.In

spring2019,signsofinfectionwerefound

on30–40percentofplantsatonesite

alongtheRiverTees,whileatanothersite

• HarmondsworthMoorinWestLondon


• therusthasoverwinteredtwice(andas
  suchnolongerrequiresphysicalrelease)
  andhasspread50m.Ateightfurthersites,
  thelife-cyclehasbeencompleted.
  Despitethesemoderatesuccesses,it is
  fairtosaythatCABI’sexperimentswith
  biocontrolintheUKhave,sofar,been
  unspectacular.Thescientistssuspectthat
  theproblemmaybe‘climaticmatching’–
  theagentsarenotcopingwiththeBritish
  weather.It is stilla longwayfromRichard
  Shaw’sdescriptionofclassicbiocontrol:
  “Releaseonce;walkaway.”

threeseparatearrivalstotheUK,from

threedifferentregionsoftheHimalayas

• Pakistan,Indiaandpossiblywestern
  Nepal.Therearenow,therefore,atleast
  threedifferentforms,knownasbiotypes,
  establishedinBritain.

Specialrelationship

Theyalsodiscoveredthatrustfungihave

co-evolvedsocloselywithbalsamthat

theywillpreferentiallyattackplantsfrom

theirownregion.Sincethestrainof

fungusintroducedhailedfromtheIndian

Himalayas,onlythoseplantsoriginating

fromthatsamehomerangewereaffected,

whichexplainsthoseearly,disappointing

results.Thetheorywasprovedwhena

secondstrainofrustfungus,thistime

fromPakistan,wasreleased,andfound

toinfecta differentcohortofbalsamina

differentregionoftheUK.

Effectivelycontrollingbalsamtherefore

dependsonmatchingtherustfungusto

thestrainofbalsamwithwhichit co-

evolved,fromthegeographicalregionit is

found.TheCABIteamnowwantstotrial

Weliveina worldthatexpectsinstant

results,butscienceis rarelylikethat.

“Abiocontrolagentofthistypewillspread

kilometresina year,”Ellisonsaid,“butyou

needa decentdensityforit toreallyspread

• tobecome‘epiphytotic’[destroyinglarge
  numbersviadisease].Thereis a lagphase,
  whichcanbefivetotenyears,whileit
  adaptstolifeintheUK.”
  GiventhattheinvasiveplantsCABIis
  workingwithintheUKgrowinorbeside
  water,whichrestrictschemicaltreatment,
  successfulbiocontrolmethodsmightwell
  beworththewait.
  Inthemeantime,therearealwaysthose
  balsam-bashingparties,I suppose.Butif
  myrivercatchmentis anythingtogoby,
  wewillneedoneheckofa party.

ANDREWGRIFFITHSisa writer

andpodcasterwhofocusesonthe

environmentandconservation.

FIND OUT MORE Our guide to

invasive plants and their biocontrol agents:

discoverwildlife.com/invasive-plants

Pretty in pink: it’s easy to

see why Victorians were

attracted to the balsam.

Right and top right: rust

fungi at work.

Clockwise from top right: CABI (x2); Nick Upton/naturepl.com; Ashley Cooper/Alamy; Theo Pike/South East Rivers Trust; Alex Hyde/naturepl.com

BBC Wildlife 35

NEWS FEATURE

August 2020