In spite of their appearance, people should not prune or remove the discolored trees. Chances are good that the trees are alive and healthy beneath their mask of red needles. Buds were well protected during the winter and will grow once spring arrives, said Jana Albers,
The most evident damage, caused by de-icing salts, occurred on white pines growing along highways. This salty water settles on the pines and is absorbed into individual needles, killing them back starting at the tips. Other damage to conifers can be caused by winter drying, or needle dehydration.
”Throughout the winter, each passing car sends up clouds of salty water,” Albers said. “Winter injury is also caused by strong, dry winds, many days of bright sunshine.” and low relative humidity that dries the needles
Some trees or groups of trees seem to get winter injury every year. It is likely the trees are stressed due to poor site conditions.
Native tree populations are adapted to their location. Moving seeds or seedlings 100 miles north or south of their site of origin can result in damage due to winter injury.
- When selecting trees to plant, choose species that are adapted to local growing conditions.
- Avoid planting white and red pines, balsam fir and white spruce within 150 feet of a highway to prevent salt damage.
- Avoid planting yew and arbor vitae on south or southwest sides of buildings or in sunny and windy locations.
- Erect temporary barriers around conifers susceptible to winter burn. They can be made of plywood, burlap, tar paper or plastics.
- Just after the snow melts and prior to bud break, rinse de-icing salts off both conifers and hardwoods.
- Reduce or eliminate the use of de-icing salts.
- Replace trees that have severe winter injury year after year. They are not in the right location and will only decline due to needle and twig loss over a period of many years.
- Keep conifers properly watered throughout the growing season and fall. Decrease the watering slightly in September to encourage hardening off. Water thoroughly in October until freeze-up.
For more information on tree care and forest health, visit www.dnr.state.mn.us/treecare/forest_health