Winter damage on conifers beginning to show up
Browning conifers may be due to winter injury.
Winter injury can affect most Christmas tree species and other conifers. The winter of 2017-18 did not seem to be colder than normal, so it is surprising to see conifers beginning to show the classic symptoms of winter injury. The warm and dry fall may have stressed trees before going into winter and could be contributing to the winter injury we are seeing. Growers are reporting they are seeing damage on many species including Dwarf Alberta spruce, white pine, Douglas-fir, Fraser, Canaan and Concolor firs. The most obvious symptom of winter injury is browning needles, especially on the south side of the tree or above the snow line.
The first type of damage we find is often called winter drying. Drying occurs when the soil is frozen and the roots cannot easily replace water when the trees loose moisture in the winter due to wind or sunny conditions. The second type is referred to as winter burn. This happens when needles or buds are damaged after rapid temperature changes. This most often occurs on the south side of the tree where the sun reflects on the snow and warms the tree during the day and then at night the temperatures drop. In a year like this, growers may be experiencing both winter drying and burn.
To complicate matters, there is also browning on Austrian pine due to Dothistroma needlecast or Swiss needlecast on Douglas fir. In addition, some trees may have died over the winter from compromised root systems caused by J-rooting or Phytophthora root rot in Fraser fir. Once you can get into the field, look closely at the trees to determine what the true cause is of the symptoms you are observing.
Damage can vary from year-to-year and site-to-site. The long-term impact depends on whether or not buds are killed. We can often see needle browning without bud-kill. If buds are also killed, which we are seeing this winter in some cases, it will take longer for trees to recover. To help trees recover, try to minimize stress this growing season through weed control, irrigation, etc.