Curing the Colorado spruce blues
OVER the years, in this column I have written about the problems associated with spruce trees. I have mentioned tip blight fungal disease has been increasing annually over the past few years. In 2012, I said that year was the worst I have seen in 40 years. Sadly, the disease has progressively worsened in 2013 and in 2014. Scientifically, the disease is known as Sirococcus conigenus. This spring, I have noticed Colorado blue spruce has been hit hard by this disease. Damage continues to be worse in spruces outside of Winnipeg. The lower half of the tree is especially targeted by this disease. Heavily diseased trees are almost dead as they cannot easily recover from severe infections of this disease.
The disease targets older and larger Colorado spruce trees. Effective treatment becomes almost impossible on these mature trees, while the infection is very light and treatable in smaller and younger spruces.
How do you recognize spruce tip blight disease?
This fungal disease causes slightly or prominently curled ends of the twigs usually denuded of their needles except on one side starting in late May or June. Advanced infections will turn the needles orange or rusty brown in colour. In recent years, a second infection period will likely occur later in July or August.
Bright yellow-green discolouration of the newer needles in parts of the tree, are often early overlooked signs of this disease. This discolouration is likely to appear in late spring, summer or early fall. The colour pattern can persist over winter and show up in the spring. A small area of Colorado blue spruce twigs near the end of the boughs can have several different colour patterns: blue, green, bright green-yellow, yellow, orange, and rusty brown. This pattern changes from year to year. The disease occurs in a tree at different stages of maturity. These stages are characterized by the colour patterns above. Ultimately, all the needles turn a rusty brown and fall from the tree. How is the disease treated? The entire tree should be spray treated with an approved fungicide such as copper, weather permitting. Usually two or three spray treatments of copper about two weeks apart are necessary in the spring and early summer (May to July), and again with a single fungicidal spray in late July to early August. This year’s on and off wet weather and strong winds are preventing the proper treatments of the disease. Maintaining a large Colorado spruce can be an expensive undertaking and can produce localized environmental concerns through fungicide sprayings.
One year of treatment is not sufficient to control the disease. The fungicide should be applied consecutively in the second and third years as well. For heavily infected trees, a fourth and fifth year of consecutive spraying will be necessary.
As I have said many times before in this column, proper fertilization of trees over several continuous years can improve a tree’s capability to contain serious fungal diseases. This will be the subject of my next column. Michael Allen is a consulting urban forester and certified I.S.A. arborist and owner of Viburnum Tree Experts. He makes house and garden visits to assess tree and shrub problems. He can be contacted by calling 831-6503 or by e-mail at email@example.com Questions can be mailed to Michael Allen, c/o Newsroom, Winnipeg Free Press, 1355 Mountain Ave., Winnipeg, MB, R2X 3B6. His web site is www.treeexperts.mb.ca
The disease Sirococcus conigenus targets Colorado blue spruce trees.