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TREE CARE: Tip blight disease threatens our spruces

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Tip blight causes needles on spruce trees to turn green-yellow.

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Tip blight causes needles on spruce trees to turn green-yellow.

I've written about the problems with spruce trees a number of times, but these issues keep returning and growing.

Within the last five years, the Sirococcus tip blight fungal disease has leapfrogged into a significant concern -- a threat not only to urban spruces but especially to shelterbelt trees on rural acreages and farms.

Sirococcus tip blight disease normally affects the current growth of spruce twigs, resulting in the death of the needles and twig tips. 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, in some instances, on one side. The needles turn a straw- or red-brown colour in the late spring before falling from the twigs.

Later in the summer, the disease returns 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 green-yellow. When the disease shows up, it has a tendency to infect nearby needles and adjacent twigs located near the original source of infection.

It surprises many people when I tell them that the interior needles of many spruce trees naturally die of old age in mature trees. This natural death process tends to coincide with the second wave of tip blight infection in late summer, producing a dramatic change in the colour of the needles. The colour changes varied from tree to tree from pale yellow to bright yellow to orange to bright orange to rusty brown.

Tip blight is a potentially lethal urban tree disease, but it tends to kill shelterbelt trees planted close together in rural areas. This disease does work with other spruce-tree diseases, such as Cytospora fungal canker (a common killer of lower spruce branches) and Rhizosphaera needle cast fungal disease, to place significant, life-threatening stress on Colorado spruce trees and, to a lesser extent, on the Manitoba white spruces.

It is getting too late to treat the disease with the first set of spray treatments right now. You could apply one spray treatment near the end of July or early August. If the disease has affected your trees, plan to do this yourself or have it done professionally again in late May or early June of 2014. The affected trees can be treated with an approved fungicide spray such as Bordeaux mixture or copper sulfate. Usually two or three spray treatments of copper 10 to 14 days apart (weather permitting) will be necessary in the spring and early summer (late May through June normally) of 2014, and again one spray treatment in late July to early August.

Properly fertilizing your spruce trees, either this fall or next spring, will significantly help them fight the disease. Strongly infected trees should be continuously fertilized either in the fall or spring for at least three years, and ideally longer. The essential nutrients in good tree fertilizers help the tree establish healthy growth to counteract the disease infections.

And don't forget to water all coniferous evergreens in the fall before the ground freezes.

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 can be reached at 204-831-6503 or viburnumtrees@shaw.ca His web site is www.treeexperts.mb.ca

Republished from the Winnipeg Free Press print edition June 22, 2013 F22

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