Dig­ging DEEP

Ex­haus­tive test­ing, re­search re­quired to di­ag­nose dis­eased trees

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

AFEW years ago I had the roots of a dy­ing Amur chokecherry tested at the Man­i­toba Agri­cul­ture Crop di­ag­nos­tic lab.

Th­ese trees were dy­ing in many di­verse lo­ca­tions in south­ern Man­i­toba. Tests per­formed on the leaves, twigs, branches and ex­posed bark did not yield any con­fir­ma­tive re­sults for a tar­get pathogen (i.e. a dis­ease).

I dis­cov­ered a client’s dy­ing Amur chokecherry tree had ex­posed roots. About one-sixth of the tree’s crown was barely alive, so I de­cided to col­lect some of the stressed twigs as well as take sam­ples of both the ex­posed and nearby buried roots. The di­ag­nos­tic lab re­sults re­vealed that there was a dis­ease in the root sam­ples, namely a very com­mon fun­gus called Fusar­ium oxys­po­rum.

This dis­ease is well known for its toxic ef­fect on plant roots. I have writ­ten about this dis­ease in my book with re­spect to its ef­fect on Amur chokecherry.

Re­view­ing some of the very ex­haus­tive lit­er­a­ture on this dis­ease pro­vides a very sur­pris­ing his­tory and in­for­ma­tion about the na­ture of this world­wide dis­ease. There is much spec­u­la­tion about the wide range of al­ter­nate hosts (both plants and an­i­mals) that ei­ther be­come in­fected or har­bour the spores of this dis­ease.

Th­ese re­mark­ably di­verse and adapt­able Fusar­ium fungi have been found in soils rang­ing from the Sono­ran Desert in the south­ern U.S. and Mex­ico to trop­i­cal and tem­per­ate forests and grass­lands, and even in the soils of the tun­dra. This dis­ease must surely be one of the most com­plex any­where on Earth. There are nu­mer­ous forms of Fusar­ium in just about ev­ery place one can look around the world.

The ques­tion I have been ask­ing my­self is, why has Fusar­ium only ap­peared — so far — on Amur chokecherry? From my own ob­ser­va­tions I sus­pect other trees in the cherry fam­ily — called Prunus — may also have prob­lems with Fusar­ium blights.

Look­ing at the re­search lit­er­a­ture on this very com­plex sub­ject, I am be­gin­ning to won­der about the re­la­tion­ships in fire blight (Er­winia amylovora) sus­cep­ti­ble fruit trees, in­clud­ing all the cherry trees with the Fusar­ium blight.

It is well known that all fruit trees can be in­fected with fire blights. Do the two dis­eases some­how work to­gether? One form of Fusar­ium blight known as Col­letrotrichum is known to af­fect ap­ple and pear fruits.

It is called blos­som-end rot of ap­ple. This sub-dis­ease is part of the very com­plex black rot dis­ease (Botryosphaeria ob­tusa) which I have writ­ten about be­fore. I will con­tinue to ex­am­ine the re­la­tion­ships among the tree dis­eases, es­pe­cially with re­spect to fruit trees. The sci­en­tific pa­pers on the in­ter­net cer­tainly help in this re­spect.

There is a com­mon Fusar­ium dis­ease that af­fects the lawn grass of many house prop­er­ties in and out­side the city. Fusar­ium blight sum­mer patch shows up in some years, but mostly does not. Typ­i­cally this patch shows up in a more or less cir­cu­lar pat­tern and can be up to a me­tre or so in di­am­e­ter. The cen­tre of this area of­ten has thriv­ing green grass. This gives it an ap­pear­ance of a bull’s eye. It is best treated by pro­fes­sional lawn-care ex­perts.

From my years of in­volve­ment with tree dis­eases, there is no ques­tion the prob­lems get more com­plex and the sub­se­quent losses of ma­ture fruit trees wors­ens with time. If you have prob­lems with fruit trees, con­tact me for pos­si­ble as­sis­tance. Michael Allen M.Sc.F., RPF (ret’d) is a con­sult­ing ur­ban forester, tree di­ag­nos­ti­cian and cer­ti­fied ar­borist. He owns Vibur­num Tree Ex­perts. His web­site is www.tree­ex­perts.mb.ca, he can be reached at 204-831-6503 or 204-2237709.


Amur cherry tree with Fusar­ium oxys­po­rum dis­ease.

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