How to save Joburg’s trees

South-east Asia’s polyphagous shot­hole borer is in­fest­ing and suck­ing the life out of South Africa’s trees

Saturday Star - - METRO -


JU­LIAN Ortlepp in­spects a dis­eased box­elder tree on Hume Road, ex­am­in­ing its trunk closely.

It’s rid­dled with clus­ters of tiny pen-sized holes. Shot­gun-like scars run like tears down its peel­ing limbs.

“Look there, see right in that tiny crack?” he ex­claims, as he finds one of the cul­prits. “There’s a lit­tle bug­ger’s back­side stick­ing out right there.”

He scrapes the tiny tree-killer out force­fully.

There’s no hope of sav­ing this street tree in Dunkeld West which, like so many other dead and dy­ing trees in the sub­urb, has been ru­ined by a ver­i­ta­ble army of highly in­va­sive bee­tles, each no big­ger than a sesame seed.

To­gether with An­drea Rosen, of the Jo­han­nes­burg Ur­ban For­est Al­liance (Jufa), Ortlepp is on a borer in­for­ma­tion ses­sion with the SA Land­sca­pers In­sti­tute around Hugh Wyn­d­ham Park, which has sev­eral in­fested tree species.

“This bee­tle is caus­ing havoc,” Ortlepp tells the group of the in­va­sion of the polyphagous shot­hole borer, which is na­tive to south-east Asia.

Its pres­ence in South Africa was first de­tected early last year by re­searcher Dr Trudy Paap of the Forestry and Agri­cul­tural Biotech­nol­ogy In­sti­tute (FABI) at the Univer­sity of Pre­to­ria.

She no­ticed small shot­gun-like le­sions on the stems and branches of ma­ture Lon­don plane trees planted along the street out­side the KZN Botan­i­cal Gar­dens.

The bee­tle car­ries sev­eral fun­gal species, one of which is Fusar­ium eu­wal­laceae, when it in­fests new trees. It bores through the bark to the sap­wood and in­oc­u­lates the fun­gus into liv­ing wood.

“The fun­gus grows in the gal­leries (tun­nels) of the bee­tle and serve as ‘veg­etable gar­den’ for the bee­tle lar­vae, but in sus­cep­ti­ble trees the fun­gus can spread through the sap­wood, caus­ing dis­ease or even death of the tree,” says FABI.

What’s alarm­ing to Paap’s col­league, Dr Wil­helm De Beer, is how fast the bee­tle is spread­ing in South Africa. It is now at­tack­ing 80 tree species, 35 of which are na­tive. Around a quar­ter of the 80 species are re­pro­duc­tive hosts in which the bee­tle in­oc­u­lates its fun­gus and then mul­ti­plies.

De Beer, who to­gether with col­leagues, is mon­i­tor­ing the spread of the bee­tle, says what sets it apart is the sheer va­ri­ety of tree species it threat­ens: agri­cul­ture, com­mer­cial forestry, nat­u­ral forests and ur­ban trees.

“Never in the coun­try’s his­tory has any in­sect at­tacked and killed trees in all th­ese sec­tors... Typ­i­cally, we deal with bee­tles at­tack­ing pine trees or avo trees but this bee­tle is at­tack­ing ev­ery­thing. It’s re­ally quite scary. The good part is that it’s not killing all the trees, but cer­tainly some species are very sus­cep­ti­ble.”

No one knows quite how it got here, but it most likely hitched a ride on tim­ber prod­ucts.

“We sus­pect it came in on tim­ber; ei­ther used for pal­let con­struc­tion or on the blocks of wood used to sta­bilise pal­lets on con­tainer ships,” says Prof Mar­cus Byrne, an Ig No­bel prize win­ner and en­to­mol­o­gist at Wits Univer­sity.

“Global in­ter­na­tional trade is al­most cer­tainly re­spon­si­ble for move­ment of the bee­tle around the world.”

De Beer points out that or­na­men­tal and street trees most af­fected in cities in­clude the Lon­don plane, box­elder, Ja­panese maple, Chi­nese maple, English oak and liq­uidamber, while na­tive trees such as co­ral trees, wild olives, yel­low woods and Natal figs are also highly at risk.

This week Jo­han­nes­burg City Parks and Zoo stated that some Lon­don planes along Jan Smuts Av­enue in Sax­on­wold had de­vel­oped a “fight­ing-back mech­a­nism,” which “hope­fully sig­nals the tail end of the out­break”.

“We’re guided by re­search find­ings to con­firm that this out­break is on its way out,” re­marks Com­mu­nity De­vel­op­ment MMC Nonhlanhla Si­fumba.

But this irks De Beer. “No, I don’t agree. The bee­tle is spread­ing fast in South Africa. We have not seen the end of this bee­tle yet. There are cer­tain species we are go­ing to lose. Some will get sick and re­cover, but a small group of trees, in­clud­ing some na­tive trees, will die quite rapidly. If there’s drought stress, too much water and wind dam­age – trees are more sus­cep­ti­ble.”

Byrne adds that what may be hap­pen­ing with the plane trees in Sax­on­wold is to be ex­pected. “Pre­sum­ably the plane trees in ques­tion have a nat­u­ral de­gree of re­sis­tance, which is al­low­ing them to hold out against the fun­gal at­tack.”

How cities dis­pose of in­fected trees is an­other ma­jor is­sue.

“We’ve seen in Joburg how some of th­ese trees are be­ing cut down and sold as fire­wood, mov­ing the bee­tle to other parts of the city such as Soweto and Lanse­ria,” says De Beer. “There, the bee­tle starts in­vad­ing again. We rec­om­mend cities have ded­i­cated places where peo­ple can dump th­ese trees.”

Ortlepp agrees. “This lit­tle bee­tle can fly 1.6km in her life­time. When we trans­port in­fected wood, we can trans­port it 10km like this,” he says.

“It’s re­ally dis­ap­point­ing that the City of Joburg has not come up with a ded­i­cated dis­posal site. We met them in April about this and we’re still wait­ing. The big prob­lem is that this bee­tle is not be­ing con­tained.”

Rosen, too, of Jufa, which works to pro­tect Joburg’s man-made for­est, which is home to an es­ti­mated six to 10 mil­lion trees, con­curs the city is not out of the woods yet.

She stresses the im­por­tance of pub­lic aware­ness and re­port­ing in­fested trees to au­thor­i­ties.

“It’s cer­tainly not our in­ten­tion to cre­ate hys­te­ria but we feel the city has done lit­tle, if any­thing. This has to be done if we are to truly at­tempt to con­tain the spread of this in­fes­ta­tion.”

There have been re­peated out­breaks of the shot­hole borer in Cal­i­for­nia and Is­rael, she says, cit­ing a re­cent US For­est Ser­vice sur­vey which showed how the borer could kill as many as 27 mil­lion trees in Los An­ge­les, Or­ange, River­side and San Bernardino coun­ties, roughly 38% of all trees in the ur­ban re­gion.

“If you look at it prac­ti­cally, you can com­fort­ably say that with­out treat­ment in 10 years’ time there won’t be any English oak trees and box­elders left in the older sub­urbs of Joburg,” says Ortlepp. “There may not be any plane trees, maples and aca­cias.”

Nor is the bee­tle go­ing any­where, cau­tions Byrne.

“We can’t erad­i­cate it. That’s one of the many prob­lems with in­va­sive species – there’s no go­ing back... The bee­tle and its fun­gus are here to stay.

“We need to find out what trees will be at­tacked by the bee­tle. What trees are sus­cep­ti­ble to the fun­gus... re­sis­tant to the fun­gus. And try to un­der­stand how the bee­tles move around, with or with­out the help of hu­mans. We should also test in­sec­ti­cide op­tions to see if the bee­tle can be con­trolled by in­sec­ti­cides.”

This, he says, is un­likely as the bee­tle tun­nels quite deeply into the tree, where in­sec­ti­cides can’t reach. Bi­o­log­i­cal con­trol op­tions us­ing its nat­u­ral en­e­mies such as host-spe­cific par­a­sitic wasps in its coun­try of ori­gin are an­other op­tion.

“Once we know lots about the bee­tle and how it be­haves in South Africa we can for­mu­late man­age­ment plans on how to con­trol it. In the in­terim, we need to con­tain the in­fes­ta­tion by not spread­ing the bee­tle around. This must be done as soon as is pos­si­ble.”

Re­port in­fested trees on What­sapp to 064 756 2736

MATTHEWS BALOYI African News Agency

TREE sur­geon Ju­lian Ortlepp in­spects a dis­eased tree for borer bee­tle in­fes­ta­tion in Dunkeld West. (ANA)|

THE polyphagous shot­hole borer and its deadly fun­gus is threat­en­ing South Africa’s trees.



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