Extension Educator, Horticulture
Take a spring stroll down any street and undoubtedly you will see an evergreen that appears more "everbrown" than evergreen. Is it some infectious disease wiping out all our trees bold enough to keep their leaves all winter? Not so fast. Many evergreens experienced winter injury from wind and salt.
Since evergreens retain their leaves over the winter they are susceptible to all the nasties of winter weather. They continue to use and lose water through their needles even when the ground is frozen. Especially during high winter wind events evergreens may lose more water than they can replace. Needles may turn completely brown or may show browning only on the tips. Brown needles may appear throughout the tree, but often show up on the windward side of the tree. White pines often show winter wind damage. Recently transplanted evergreens are more susceptible to winter injury due to their reduced root system.
Both young and mature trees can also show browning from salt spray from deicing salts. The damage is more prevalent in high traffic areas along interstates or city streets. Salt damage appears on one side of the tree. Salt spray damage typically will show on all evergreens facing the street not an individual tree in a row.
Don't give up on brown evergreens just yet. They may look fatally dramatic; however, if the branch and growing bud is still alive they have a chance to grow. First scratch a stem with your thumbnail. If the stems are green and appear pliable, they are probably still alive. If the stem is dry and brown than that portion or the entire plant may be dead. Also look at the buds at the tips of branches. Sacrifice one and see if it is still green. Green is good. As long as the buds are alive the branches may grow and eventually fill in the area thinned by needle loss.
If the evergreens started showing decline or browning last fall, the source of the decline goes beyond winter damage. Insects and disease problems can also damage evergreens as can environmental stresses of drought or flooding or poor maintenance practices such as over-fertilizing.
The pattern of affected plants in the landscape can lead to clues to the problem. Most diseases begin in hot spots and slowly spread from those spots. Infectious diseases rarely affect a line of trees at once or appear seemingly "overnight". Look at similar trees in the community. If all the pines in the area are affected, environmental stress is more likely. Needle browning on a wide variety of evergreen plants such as pines and spruces typically is also environmental and not an infectious disease or insect problem.
Identifying the evergreen species is also crucial in narrowing the possible suspects of decline. Each species has its own set of common problems.
For example Scotch pine is highly susceptible to pine wilt disease caused by the pinewood nematode whereas white pines are resistant.
Home owners have reported a sudden decline of one white pine in the midst of other healthy white pines. The trees most likely are suffering from white pine decline which involves many stress factors such as poorly drained soils or windy sites working together to cause tree decline and often tree death. An infectious disease is not usually involved in white pine decline.
With good maintenance practices evergreens should recover well from winter injury. Watering during dry periods and mulching with 3-4 inches of wood mulch can help trees to recover, stay healthy and hopefully be in better shape for next winter.
Information on evergreen insects and diseases http://www.urbanext.uiuc.edu/focus/index_evergreen.html