Conifers, or evergreen trees, provide color and wind protection to the Iowa landscape during the winter months. However, this year, many of these trees are showing signs of winter desiccation, also known as winter burn.
Although this past winter may have been one of the warmer on record, several days had air temperatures above freezing, while the soil remained frozen.
“When this happens, conifers use the water reserves they have in their needles, but are unable to absorb new water from the frozen soil,” says Tivon Feeley, DNR forest health program leader. “Because roots in frozen soil have no ability to replace water, winter burn occurs as needles dry out and brown. The tree literally runs out of water.”
Symptoms of winter burn include browning or bleaching of needles and loss of needles, which can eventually lead to death. The symptoms tend to be worse on the windward side of the tree and become more apparent as the days become warmer.
According to Feeley, the DNR is beginning to receive calls about arborvitae, white pine and white fir with moderate to severe damage from winter burn, and he expects the damage will become more apparent in June and July.
If needles on trees are dead but buds are alive, new plant foliage will regrow to replace the winter burned foliage; however, if both the buds and needles are dead, the tree will not recover and will need to be removed.
“There is no way to prevent winter burn,” says Feeley, “however, you can reduce the risks by properly mulching around your conifers and watering in the fall just before the trees goes dormant.”
“Watering is especially important in drought years,” adds Feeley, “and therefore the DNR does not recommend conifers for newly planted windbreaks. Deciduous trees generally have fewer disease and insect problems, and grow quicker, resulting in faster protection.”
For more information about winter burn and other tree-related issues, contact a DNR district forester in your area. For a list of DNR staff by county, visit www.iowadnr.gov/contact.