Un­der­stand­ing cit­rus green­ing and Asian cit­rus psyl­lid

The Orchardist - - >>contents - By Wendy Lau­ren­son Pho­tos cour­tesy Nikki John­son ex­ec­u­tive man­ager, NZCGI.

To get an un­der­stand­ing of the dis­ease and the threat it poses, a cit­rus in­dus­try team of two New Zealan­ders and six Aus­tralians re­cently spent 10 days in both Florida and Cal­i­for­nia. Brad Davies, NZCGI (New Zealand Cit­rus Grow­ers Inc.) Man­darin Prod­uct Group chair­man and Kerik­eri cit­rus grower, and Nikki John­son, ex­ec­u­tive man­ager of NZCGI, were the New Zealand del­e­ga­tion.

Cit­rus Aus­tralia ini­ti­ated the trip and in­vited the New Zealand cit­rus in­dus­try to be part of it. Most of the Aus­tralians in the team were at a State Gov­ern­ment level in­volved in biose­cu­rity re­sponse plan­ning along with one Fed­eral Gov­ern­ment rep­re­sen­ta­tive and the tour leader from Cit­rus Aus­tralia. “With the scale of im­pact to the cit­rus in­dus­try in Florida and po­ten­tially Cal­i­for­nia, we need to be in­formed and pre­pared,” Brad says. “Ev­ery­one in­volved in the trip was open and oblig­ing with in­for­ma­tion and very gen­er­ous with their time.”

Cit­rus green­ing is also known as huan­g­long­bing (HLB), a Chi­nese word that means “yel­low shoot dis­ease”. Brad ex­plains that HLB is a pathogen that gets into the phloem of the plant, blocks the vi­tal pas­sage­ways, and is fa­tal to the tree. The main way it is spread is by the Asian cit­rus psyl­lid – “a dif­fer­ent psyl­lid from the one we have here af­fect­ing the potato fam­ily.”

The Florida cit­rus in­dus­try has been fight­ing cit­rus canker in re­cent years, so they didn't re­alise that in the mean­time cit­rus psyl­lid was there spread­ing HLB. By the time they re­alised, 40% to 50% of the trees were al­ready in­fected. “It's a huge is­sue in Florida and we drove past big or­chards with trees in var­i­ous stages of de­cline. In­fected trees con­tinue to pro­duce, but in less vol­ume, and of­ten the fruit aborts be­fore ma­tu­rity. There has been 30% re­duc­tion in pro­duc­tion there year on year. Eighty per­cent of the Florida cit­rus in­dus­try is based around juice, so the flow-on af­fect is the loss of 70,000 jobs.”

Cit­rus pro­duc­tion costs in Florida have dou­bled in the bid to com­bat the psyl­lid, and re­turns are a lot less be­cause of fall­ing pro­duc­tion vol­umes. Some grow­ers have walked away. “We left Florida feel­ing like they may be fight­ing a los­ing bat­tle.”

Cit­rus green­ing, spread by Asian cit­rus psyl­lid, has dev­as­tated 60,000 acres of cit­rus trees in Florida since it was de­tected in 2005 and has taken 70,000 jobs with it. “With the scale of im­pact to the cit­rus in­dus­try in Florida and po­ten­tially Cal­i­for­nia, we need to be in­formed and pre­pared.”

The ex­tent of dam­age in Florida has alerted the cit­rus in­dus­try in Cal­i­for­nia. Cal­i­for­nia has had time to see the scale of the im­pact so is be­ing pro-ac­tive. They are putting a huge ef­fort into man­ag­ing (mostly spray­ing) the Asian cit­rus psyl­lid pop­u­la­tion to re­duce the risk of spread of HLB. It's a stop­gap mea­sure to buy time un­til a greater so­lu­tion is found. “When we were in Cal­i­for­nia, only one tree in the State (in Los An­ge­les) had been found to be in­fected with HLB, but there is a huge res­i­den­tial pro­gramme in place man­ag­ing peo­ple's back­yard cit­rus. The source of the in­fec­tion in that sin­gle tree was likely un­cer­ti­fied plant ma­te­rial. This tree had been bud­ded some15 times by a home gar­dener with many un­known va­ri­etal types. HLB could be out there in ran­dom cit­rus trees that die, but un­less it is part­nered with Asian cit­rus psyl­lid, it won't spread – other than by in­fected tree ma­te­rial be­ing spread.”

So­lu­tions to HLB and Asian cit­rus psyl­lid are so far elu­sive. Brad says there don't seem to be any resistant va­ri­eties yet, but ob­vi­ously re­search is be­ing done to find or de­velop th­ese. While most of the cur­rent pest and dis­ease man­age­ment ef­fort is go­ing into spray­ing the psyl­lid, they have iden­ti­fied a bio-con­trol par­a­site Ta­ma­raxia and have a ma­jor breed­ing pro­gramme for it in place to help man­age the psyl­lid pop­u­la­tion, how­ever its ef­fects are limited.

Ob­vi­ously the Aus­tralian/New Zealand team was as­sess­ing readi­ness and re­sponse op­tions for the cit­rus in­dus­try down- un­der if HLB and the Asian cit­rus psyl­lid ap­peared here. “Com­ments from the Amer­i­can pro­fes­sors made it clear that con­di­tions favourable for grow­ing cit­rus are the same con­di­tions favourable for HLB and Asian cit­rus psyl­lid. Any in­cur­sion of HLB here would be through move­ment of in­fected plant ma­te­rial. Ma­te­rial im­ported through quar­an­tine is tested be­fore re­lease so the big­gest risk is an in­cur­sion through il­le­gally im­ported plant ma­te­rial. So again this high­lights that we need to be ab­so­lutely vig­i­lant around our biose­cu­rity.”

“We were stag­gered at the re­sources be­ing in­vested in HLB and its spread in Florida. The dis­ease is ob­vi­ously a huge risk to the Cal­i­for­nia in­dus­try and they are in­vest­ing heav­ily in de­tec­tion and preparedness. In New Zealand we would have to be pre­pared to have a fight­ing fund to al­low early de­tec­tion and erad­i­ca­tion. The team's re­sponse after this trip though, was that if the dis­ease and psyl­lid es­tab­lished here, the cit­rus in­dus­try would strug­gle to sur­vive.”

Trees dy­ing from Cit­rus Green­ing in Florida. Cit­rus green­ing in Florida.

Brad Davies in Ta­ma­raxia (bio-con­trol par­a­site for cit­rus psyl­lid) breed­ing fa­cil­ity in Cal­i­for­nia. L-R Nick Se­comb, South Aus­tralia State Gov­ern­ment, Brad Davies, and a re­searcher from Florida, in a Univer­sity of Florida re­search or­chard. Asian Cit­rus P

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