Karen Ripley, Forest Health Program Manager, Washington Department of Natural Resources
“I went away on a two-week vacation. When I came home, my pine trees had all turned brown!” Kettle Falls landowner, late summer 2014
Although tree crowns suddenly turn brown for a variety of reasons, the timing of the color change can sometimes be an indicator of the causes. For example, disease impacts from the previous year become apparent in the spring as new buds open and older needles die, while bark beetle damage shows up later in the year as the damaged trees and branches dry and turn red.
When trees turn brown quickly in mid-summer like our Kettle Falls landowners’, there are three likely causes: fire, chemicals or hail. While it’s always best to consult a professional, here is some information to help you identify the potential sources of the damage:
A group of newly scorched trees may make you look twice as you drive by at 55 mph, but the tell-tale blackening of the affected ground and debris are usually fairly obvious and persist for months or years. The damage to the trees’ foliage is generally concentrated in the lower crowns. The scorched needles may be intact, but there you won’t see the tell-tale dots left by fungus fruiting bodies. The needles are usually cast from injured branches relatively quickly, but they can remain attached to fire-killed branches for several years.
Damage from herbicides or de-icers is usually concentrated to the areas where the products were applied. The symptoms appear from early spring into summer as the affected tissue dries out. Right-of-way vegetation and the sides of trees facing roadsides may exhibit killed or yellow-flecked foliage. The foliage will appear intact, without any missing or eaten portions, but injured portions could be sunken or shrunken. Sucking insects can cause similar mottling, but insects usually leave shed exoskeletons or webbing as well. Chemical damage can also be extremely consistent in appearance – much more so than damage from insects. Many herbicide ingredients mimic or interfere with plant growth hormones, and commonly lead to abnormal shapes and sizes of shoots and leaves.
Hail stones melt quickly but damage symptoms became apparent immediately and can persist for several years. Think about how hail stones fall and how the storms containing hail approach. The storms are usually sudden, with fierce wind gusts, so the side of the tree or forest facing the storm is where the damage generally occurs. The size of the affected area can vary widely, with sudden transitions from severe to no apparent damage.
Tree damage (broken, ripped, abraded or pitted branches, bark and needles) will be concentrated on the upper crowns and surfaces of the branches. The upper and unprotected foliage may be knocked to the ground, while protected interior or lower foliage may appear green and intact.
Injury from hail is inflicted suddenly so the damaged trees will appear to be in the same stage of injury or recovery. Although some physical changes occur immediately (fallen foliage, broken bark or branches), the injured needles dry out quickly in the warm days of summer, making the color changes more conspicuous and rapid than many other types of insect, disease or physical activity.
One way of finding out if hail has occurred near your woodlands is to determine a date range for the damage, and then check those dates on NOAA’s Storm Prediction Center to see if hail was verified or reported in your area.
If your trees are damaged by hail, consider the following as you assess the damage:
- The loss of upper, exterior foliage is more significant to a conifer tree than the loss of its lower, interior foliage.
- Although forest managers always try to maintain at least 30 percent of the height of a tree in a live crown, vigorous trees that receive fire injuries from below or insect defoliation from above can survive with less than 30 percent of their live crown remaining.
- After the injured or dead foliage has dried out, check the survival of twigs and branches by examining some of the remaining buds. Slice the bud lengthwise with a sharp knife. If the bud tissue is green and succulent, the bud and the twig it is attached to are still alive. If the bud is brown and punky, that portion of the branch or twig may have died.