Fun­gus causes dis­coloura­tion

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

This spring sea­son has been a very busy one for me with lit­er­ally many dozens of peo­ple call­ing or e-mail­ing me about the sit­u­a­tion with sud­den nee­dle dis­coloura­tion in their spruce trees. What is go­ing on I am asked? There is not un­for­tu­nately a sim­ple cause and ef­fect an­swer. Over the many years I have been as­so­ci­ated with the care of trees on the Prairies and north­west­ern On­tario, the num­ber one tree con­cern I re­ceive above all oth­ers re­lates to spruce trees – Colorado blue spruce, our in­dige­nous white spruce, and on rare oc­ca­sions, Nor­way spruce. Sud­den nee­dle fall and dis­col­oration can be caused by ex­ces­sive rain, ex­ces­sive heat, ac­cu­mu­la­tive years of growth stress and es­pe­cially by a slowly act­ing po­ten­tial lethal canker dis­ease. Along with Cy­tospora there are spruce tip blight, sooty mold and nee­dle cast dis­eases.

Re­ac­tion to cli­matic ex­tremes is not the only fac­tor in­volved with spruce nee­dle dis­coloura­tion. Nearly all spruce trees in south­ern Man­i­toba 15 years and older have a slowly lethal fun­gal canker dis­ease called Cy­tospora. I re­fer to it as the white blis­ter dis­ease. It is an in­dige­nous dis­ease to Man­i­toba white spruce. the other dis­eases also con­trib­ute to the nee­dle brown­ing sit­u­a­tion.

Cy­tospora dis­ease dis­plays sev­eral forms on the tree as signs of in­fec­tion. There is no known cure for this fun­gus canker dis­ease which is the most com­mon and most widely spread dis­ease of or­na­men­tal spruce trees in south­ern Man­i­toba. Here is a de­scrip­tion of this com­plex dis­ease

(1) In the early stages, newly formed cracks or le­sions will ex­ude a clear resin-sap. The dis­ease has suc­cess­fully killed the liv­ing wood cells un­der the bark at this time. Soon af­ter the clear resin will ox­i­dize into an am­ber colour and then to white-grey colour of­ten crys­talline in ap­pear­ance.

(2) Look for resinous white blis­ters on the lower or mid­dle branches and/ or resin bleed­ing from cracks in the bark of the trunk. Of­ten these blis­ters are bluish-grey in colour in very ac­tive stages of the dis­ease.

(3) On some trees there can be nu­mer­ous soft ch­est­nut brown blis­ters that are ap­prox­i­mately oval in shape and be ½ to 2 inches in length. This is an­other phase of the Cy­tospora dis­ease.

(4) Old blis­ter sites will show resin­sap ac­cu­mu­la­tion that grad­u­ally dis­colours with age. The old swollen blis­ters can be a muddy orange brown or black.

Treat­ment op­tions are very limited, but here are some sug­ges­tions:

(1) Some ar­borists will spray the branches with fixed cop­per but there is no ev­i­dence that this is ef­fec­tive on the in­ter­nal canker fun­gus. Fungi­cide sprays can be sprayed onto the nee­dles to help con­trol the spread of the nee­dle blight but it would need to be done in

(2) late sum­mer be­fore the nee­dles turned colour. This is not a prac­ti­cal so­lu­tion as the on­set of nee­dle dis­coloura­tion can be sud­den and move through the tree very rapidly.

(3) Timely re­moval and dis­posal of the dead and sig­nif­i­cantly in­fected branches (a san­i­ta­tion process) on all spruce trees are the first ac­tions that should be taken. Prune dead branches back to the bark of the trunk or liv­ing larger branches that is at the point of at­tach­ment.

(4) Keep­ing all spruce trees healthy through reg­u­lar aer­a­tion, fer­til­iza­tion and wa­ter­ing will sig­nif­i­cantly slow the rate of ex­pan­sion of Cy­tospora white blis­ter canker dis­ease and other dis­eases such as tip blight dis­ease, nee­dle cast dis­ease, and nee­dle rust dis­ease. Fer­til­iza­tion how­ever will not cure the dis­ease. The spruce twigs and nee­dles will how­ever show much im­proved size, colour and growth.

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