Spring Clean Up Reveals Winter Damage To Trees And Shrubs
Friday, May 30, 1997
FORT COLLINS--As gardeners clean up their trees and shrubs
for spring, winter damage is beginning to show.
Colorado State University Cooperative Extension plant
pathologist Bill Brown said0, "Much of Colorado's Front Range
experienced a dry winter, which naturally leads to a lot of
damage. Some of that damage won't be obvious until mid summer,
when temperatures zoom up and trees and shrubs exhibit stress
from lack of moisture."
Root injury, foliar browning and die-back or injury to stems
are three of the most common symptoms caused by freezing injury.
These symptoms often result from one or more of the following
three winter problems.
Damage to shoots or stems: Early autumn frosts often injure
growing or partially hardened shoots. Brown said late-fall
applications of fertilizer and water can prolong shoot growth and
result in frost injury of the late growth, which hasn't developed
cold hardiness. Although various parts of the tree or shrub may
be exposed to different temperatures, only portions of the plant
may exhibit visible injury.
Desiccation injury: Winter injury to conifers is due more to
shoot desiccation than to cold damage. Severe damage can kill the
leaves, buds and even trees. Winter-desiccation injury occurs
when the cold and frozen soil keeps the roots from absorbing
enough water to keep up with transpiration losses. In human
terms, that means the tree "sweats" more than it can "drink."
Winter winds add to the problem by increasing the transpiration
loss. This is when many trees experience severe needle burn. The
needles begin to turn brown at the tip and even further back in
severe cases. Damage usually is most severe on south and
southwest sides of trees, but damage is variable within different
species of trees and shrubs.
Root injury: Roots usually are hardier than stem tissues
because soil and snow cover protects them from exposure to
freezing air temperatures. If left unprotected, however, Brown
said small feeder roots may be injured or killed when the soil
does freeze. Mulching trees and shrubs can help control root
injury caused by freezing.
Brown noted that shallow tree roots in poorly drained soils
may already be stressed and frequently are more heavily damaged
by frost than roots in well-drained soils. In the first warm days
of spring, new shoots and leaves that wilt and die indicate
winter root damage.
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