Growing Green: Tree Ailments Affecting Our Conifers
This has been the summer for “stressed tree” questions, specifically regarding conifers. Just drive around Alexandria, and you will see dead and dying conifers, some of them mature trees that have thrived for many years. What is causing this and what can be done about it? “A number of factors, including prolonged drought and spruce needle rust, can lead to dead or dying evergreen trees this time of year”, says Jana Albers, DNR Northwest Region Forest Health Specialist.
Minnesotans have experienced moderate to severe drought for eight of the past eleven years. Conifers growing along the edge of lakes, wetlands and ditches have suffered from fluctuating water tables. (Remember the flooding from the summer of 2011?) Trees in standing water for weeks on end lose their lowermost roots. Then, when water becomes scarce, the root systems don’t extend down far enough to reach the low water table. Tree health suffers as photosynthesis shuts down and reserves of sugars and starches are depleted. In a few droughty growing seasons, trees, especially balsam firs, and white and black spruce, die of starvation.
Red, white and jack pines have suffered a similar fate, although root death due to fluctuating water tables was not involved. Photosynthesis was shut down for days or weeks during periods of drought over the past decade. Trees used up their starch and sugar supplies, and couldn’t replenish their reserves in subsequent years due to the extended drought. Eventually their reserves were exhausted and these trees also died of starvation.
There is hope! The spring and early summer of 2013 saw a period of vigorous tree growth and a restoration of sugar and starch reserves.
If you are seeing your spruce trees turning tan, yellow, orange or pink, your trees may be infected with the spruce needle rust fungus – which is an aesthetic problem, but seldom a tree health problem. Spruce needle rust infects current-year needles of blue, white and black spruce. Infected needles will turn color and then shed in the fall. However, healthy buds on the ends of branches will produce new needles next year. Chemical control with fungicide is usually not helpful. The DNR recommends keeping spruce trees healthy during a spruce needle rust outbreak by watering trees during dry periods, avoiding sprinklers to keep needles dry and minimize the spread on infection. Mow weeds and grass around small trees, and mulch around trees to maintain soil moisture and discourage weed growth. (Keep mulch away from the tree’s trunk.)
For more information about spruce problems, visit: www.extension.umn.edu/distribution/horticulture/M1265.html.
Robin Trott is a Horticulture Educator with University of Minnesota Extension.