In the last three weeks the ISU Plant and Insect Diagnostic Clinic has received Norway spruce, blue spruce and concolor fir images (Pictures 1 and 2) and plant samples with symptoms of frost injury. Jesse Randall, ISU Extension Forester has reported damage in locations around the state. Susceptible plants include spruce, fir, Douglas fir and occasionally pine.
Frost injury symptoms include dying and curling shoot tips sometime appearing only on one side of the tree or on trees that are on a low or exposed location or frost pockets. The tips curl over a short time period and many tree owners attribute this incorrectly to herbicide drift. Herbicide injury will also damage other parts of the tree in addition to the new growth. See the US Forest Service bulletin for more information.
The symptoms associated with frost are a quick development of curled tips and the symptoms may be concentrated on west and/or sides of the trees or windbreak. On May 9, weather alerts reported freeze warning from 3:00 am until 9:00 am in Story County, IA that produced widespread frost and freezing temperatures in many locations. At that time, most of evergreen mentioned above were forming this year new tender needles. Dead shoot tips might not be very evident until 2-3 weeks later. Susceptible trees may become stunted or bushy if injured by frost several years in a row. The trees will not be killed by the loss of some of their shoot tips but may look misshapen as laterals take the role of shoot tips. Live, crooked shoots may also be seen late in June or July. Some dead shoots might remain on trees until late fall or next spring. This can be corrected by pruning out the curled tips back to a live bud or side branch.
There are other reasons among disease and insect damage for the tips to curl on a spruce or pine but it will not happen all at once. Trees infected with a borer for example will have randomly scattered curled tips rather than the injury concentrated on one side of the tree. Read more at Purdue University Extension Plant and Pest Diagnostic Lab report.