Birch tree de­cline may not just be old age

Winnipeg Free Press - Section F - - HOMES - MICHAEL ALLEN

OLDER birch trees will nat­u­rally show signs of their ad­vanc­ing years as var­i­ous branches start to die. If they die within the crown of the tree it is likely due to age. If the branches die from the top and grad­u­ally show a pro­gres­sive pat­tern of dy­ing branches year af­ter year through the crown, then the cause is likely to be a re­sult of in­ter­nal wood feed­ing ac­tiv­ity of the bronze birch borer – the grub­like lar­vae of the adult which is iden­ti­fied by its bronze head and a grey-black body.

The first sign of this pest is the pres­ence of dy­ing branches near the top of the tree. Usu­ally the leaves shrivel up and turn brown. With care­ful ob­ser­va­tion, es­pe­cially with binoc­u­lars, the pres­ence of ‘ripple or mus­cle’ bark can be seen in in­fested branches or the stems near the top of the tree. The rip­pling is in­ter­nal cal­lous wood cre­ated by the tree to limit the feed­ing area of the grubs. The grubs con­sume the liv­ing wood un­der the bark thereby girdling the af­fected area at the feed­ing zone. This liv­ing wood con­tains con­duct­ing col­umns of cells that trans­port wa­ter and nu­tri­ents to the leaves. Girdling cuts off this sup­ply caus­ing the leaves on the af­fected branches and stems to wither and die.

There is no ap­proved in­sec­ti­ci­dal con­trol for this pest once it’s in the tree. It is es­sen­tial to re­move the top dy­ing branches when they first show up as soon as pos­si­ble to stop the down­ward spread of this in­sect in the tree. In ad­di­tion to the ripple ap­pear­ance of the bark, there are hor­i­zon­tal ‘D’ shaped exit holes caused by the newly emerg­ing adult bee­tles. All signs of the bee­tles’ pres­ence on the tree’s stems and branches should be re­moved. It is usu­ally nec­es­sary to cut into ap­par­ently liv­ing wood with healthy look­ing leaves. It is very im­por­tant to hire a skilled arborist who can climb the tree to de­tect the beetle’s pres­ence and be able to re­move the in­fested branches and stems.

In younger white birch trees I have no­ticed a dis­ease called crown gall. It also oc­curs in other trees as well. Swellings of the stems, branches of­ten pro­duc­ing a dis­tinct gall are signs of this dis­ease. ‘Witches brooms’ or clus­ters of twigs from a com­mon ori­gin can also ap­pear with this dis­ease. Young trees are most sus­cep­ti­ble to this dis­ease as the fun­gus dis­ease can gir­dle or de­stroy the liv­ing tis­sues un­der the bark of twigs and stems, con­se­quently killing the tree. Older trees usu­ally can with­stand the girdling ef­fects of this dis­ease as it rarely does any sig­nif­i­cant in­jury to the tree. It is not un­com­mon for this dis­ease to be as­so­ci­ated with the bronze birch borer in the same tree.

Pre­ven­tion of this dis­ease is key to hav­ing a healthy tree. Never pur­chase a woody shrub or tree show­ing woody swellings or galls. Look very care­fully at the bark of a birch that you want to pur­chase. The sur­face of the bark should be smooth and should not have any vis­i­ble swellings or bumps. If a small gall de­vel­ops on a pre­vi­ously un­in­fected tree, it can be care­fully re­moved if it is on a twig or small branch. If it is on the trunk, it is es­sen­tially im­pos­si­ble to treat. The tree has to be re­moved once dead por­tions of the crown show up. If a gall is small enough, on a large stem or branch, it can some­times be sim­ply cut off with a very sharp knife. The ex­posed wood can then be sealed with an in­ert tree prun­ing paste or seal. Michael Allen M.Sc.F., RPF is a con­sult­ing ur­ban forester, tree di­ag­nos­ti­cian and cer­ti­fied arborist. He owns Vibur­num Tree Ex­perts, a Man­i­toba com­pany that pro­vides ob­jec­tive as­sess­ments of the con­di­tion and the care re­quired for trees and shrubs on home and busi­ness land­scapes. He does make house and gar­den calls. He can be reached at 204-831-6503 or at vibur­numtrees@ His web site is www.tree­ex­


If the branches of a birch tree die from the top, the cause is likely to be a re­sult of the in­ter­nal wood feed­ing ac­tiv­ity of

the bronze birch borer.

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