Siro­coc­cus dis­ease a blight on spruce trees

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

OF all the tree is­sues that con­cern prop­erty own­ers, un­ques­tion­ably Colorado blue spruce and the green va­ri­ety of Colorado spruce year after year top the list. This va­ri­ety and species of spruce sim­ply has lost most of its abil­ity to deal with a host of dis­ease and pest is­sues. I have writ­ten about the prob­lems with spruce trees a num­ber of times, but as a topic, the prob­lems with th­ese trees con­tinue to cause stress for many peo­ple who have th­ese trees. With­out ex­cep­tion, of ev­ery Colorado spruce I have ex­am­ined this year — and I have looked at many hun­dreds — tip blight fun­gal dis­ease (also called Siro­coc­cus) shows up con­sis­tently in trees over 10 years of age and oc­ca­sion­ally in those younger in age. Tip blight fun­gal dis­ease — an in­dige­nous dis­ease in Man­i­toba white spruce and black spruce — has be­come epi­demic through­out ur­ban and ru­ral Man­i­toba. Siro­coc­cus tip blight dis­ease nor­mally af­fects the cur­rent growth of spruce twigs, re­sult­ing in the death of the nee­dles and tips of twigs. The dis­ease causes slightly or promi­nently curled ends of the twigs start­ing in late May or June. In­fected twigs are de­nuded of their nee­dles, ex­cept on one side in some in­stances. Later in the sum­mer, the dis­ease re­turns in many trees to change the nee­dle colour at the ends of the twigs to a bright green-yel­low. In Colorado blue spruce, this dis­coloura­tion is of­ten very dra­matic. The blue nee­dles turn bright green and then slightly dis­colour to a bright green-yel­low later into the sum­mer. The nee­dles turn a straw to red-brown colour in the late sum­mer as they die be­fore fall­ing from the twigs. This coloura­tion pat­tern sim­ply did not show up in Colorado spruce ear­lier than seven years ago. Other fun­gal dis­eases such as spruce nee­dle cast turns nee­dles a dark pur­ple-brown es­pe­cially near the lower part of the tree. With­out ex­cep­tion, all spruces will be in­fected with a slow-killing fun­gal dis­ease sim­ply called Cy­tospora. The dis­ease re­sides inside the crit­i­cal cam­bial area just un­der the bark. As cer­tain cam­bial cells die, they re­lease a clear liq­uid in­fected with the dis­ease. The clear colour slowly turns grey-white, which be­comes very ev­i­dent as ver­ti­cal streaks down the ex­te­rior of the trunk bark. Branches also be­come heav­ily in­fected. Older streaks will dis­colour into a pale yel­low colour. On oc­ca­sion, you might see a royal blue colour in those streaks. Cy­tospora dis­ease tends to kill the lower branches first and then work its way up the tree. It does have a ten­dency to pass over sum­mer branches with­out killing them. Un­treated Cy­tospora and tip blight will even­tu­ally kill most if not all of the tree. Both tip blight and nee­dle cast dis­eases are treat­able with two or prefer­ably three cop­per fungi­cide sprays spaced out dur­ing the sum­mer. Treat­ment is best done by li­censed spray ap­pli­ca­tors. Un­for­tu­nately, the treat­ments need to be re­peated an­nu­ally un­til there are no longer any signs of this dis­ease. Why is this prob­lem hap­pen­ing with the spruce? Colorado spruce has been ma­nip­u­lated by hor­ti­cul­tur­ists since 1926. In or­der to ob­tain the per­fect-shape tree with deep blue or blue-grey colours, the dis­ease-resistant genes have been vir­tu­ally weak­ened to the ex­tent they sim­ply can no longer pro­tect this species of spruce. Sci­en­tists back then pre­dicted that this tree would fail to thrive in the ur­ban and ru­ral land­scape. Prop­erly fer­til­iz­ing your spruce trees next spring will sig­nif­i­cantly help the spruces fight the dis­ease. Strongly in­fected trees should be con­tin­u­ously fer­til­ized ei­ther in the fall or spring for at least three years ide­ally longer. The es­sen­tial nu­tri­ents in good tree fer­til­iz­ers help the tree es­tab­lish healthy growth to help coun­ter­act the dis­ease in­fec­tions. Hope­fully, prop­erty own­ers should have al­ready wa­tered all of their conif­er­ous ev­er­greens this fall be­fore the ground froze. Michael Allen M.Sc.F., RPF (ret’d) 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. If you would like your prop­erty trees as­sessed, he can be reached at 204-831-6503 or by e-mail vibur­numtrees@shaw.ca His

web­site is tree­ex­perts.mb.ca. Michael’s new book, Dr. Tree’s Guide to the Common Dis­eases of Ur­ban Prairie Trees, is avail­able from the au­thor or from

McNally Robin­son and Chap­ters book­stores.

Mas­sive Cy­tospora fun­gal dis­ease in­fec­tion and typ­i­cal ‘bleed­ing’. The orange blob is a gall pro­duced by an in­sect called the spruce pitch mass borer

that likes to in­fest stressed spruce trees.

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