News from the gar­den­ing world

Na­tive ash trees un­der threat as pest pushes west

Garden News (UK) - - News - Words Ian Hodg­son

Adev­as­tat­ing ex­otic pest has caused five of the six most prom­i­nent ash trees in North Amer­ica to be a step away from ex­tinc­tion – and now the UK pub­lic is be­ing urged to keep a watch­ful eye out in case it reaches th­ese shores.

The Asian emer­ald ash borer bee­tle, na­tive to China, Ja­pan, Tai­wan, Ko­rea and the Rus­sian Far east, has dec­i­mated the North Amer­i­can ash pop­u­la­tion, caus­ing the In­ter­na­tional Union for Con­ser­va­tion of Na­ture (IUCN) to place the five species on its ‘crit­i­cally en­dan­gered’ Red List. Three species, the white ash, Frax­i­nus amer­i­cana, the black ash, F. ni­gra, and the green ash F. penn­syl­van­ica, are the coun­try’s most dom­i­nant species, com­pris­ing nine bil­lion trees.

The half inch-long metal­lic green bee­tle ar­rived in Michi­gan on in­fested wooden pal­lets in the late 1990s. Its grubs bur­row be­neath the bark, feed­ing on the tree’s liv­ing tis­sues, girdling it and caus­ing it to die within two to three years. Sci­en­tists es­ti­mate bee­tles can de­stroy an ash plan­ta­tion in just six years.

There’s cur­rently no known method of con­trol­ling the pest or re­sis­tant species, ex­cept the na­tive Asian Manchurian ash, F. mand­shurica, although work is on-go­ing to find a so­lu­tion.

Thank­fully, the dis­tinc­tive bee­tle hasn’t been found in the UK or the EU, but is cur­rently 150 miles be­yond Moscow, trav­el­ling west at around 25 miles per year. The Forestry Com­mis­sion is ex­tremely con­cerned about the in­sect ap­pear­ing in the UK, as it will at­tack our na­tive ash, Frax­i­nus ex­cel­sior, much of it al­ready weak­ened or killed by re­cent out­breaks of chalara, a fun­gal disease in­tro­duced to the UK in 2012.

The bee­tle has been placed on the UK Plant Health Risk Reg­is­ter and the Forestry Com­mis­sion is ask­ing the pub­lic to be­come fa­mil­iar with the borer bee­tle, re­port­ing any sus­pected cases. l Visit emer­al­dash­borer.

Ash trees are an im­por­tant el­e­ment in the Bri­tish land­scape

Trees a acked by the emer­ald leaf borer (be­low) even­tu­ally die back

Tun­nelling by grubs de­stroys liv­ing tree tis­sue

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