Control PLANT DISEASES
For Better Farming And Better Living

Mimeo BP 2-10

WINTER INJURY AND DROUTH DAMAGE
TO ORNAMENTAL EVERGREENS

The combination of dry summer and fall weather and low tem-
peratures during the winter or early spring months may cause
damage to evergreens and other shrubs used for ornamental plant-
ings around city homes.
Winter injury (and drouth damage) may cause a dying back of
the branches and twigs of evergreens, such as Red Cedar, Arbor-
vitae, Pfitzer Juniper, Andorra Juniper, Prostrate Juniper. De-
ciduous shrubs, such as Spiraea and privet also may be damaged.
In the early spring, trees and shrubs damaged from this cause
will appear brown and dried out at the tips of the branches and
twigs and will fail to leaf-out normally. In some cases, dam-
aged shrubs may leaf out in the spring but will die back within
3 or 4 weeks. The bark of branches may even be killed. Cases of
winter injury may not show up until a year or more after the dam-
age has occurred. Winter injury may be difficult to distinguish
from diseased conditions.
Winter injury may be caused by several factors. Spring
frosts, with temperatures below freezing in very late spring
after new growth is well advanced, will cause "winter injury".
This is especially true when ornamental trees and shrubs are
located in hollows and valleys where "frost pockets" may occur.
A cool summer, followed by a warm early fall with unseasonable
cold in late October or early November, may result in "winter
injury". Under such conditions, twigs and branches of ornamen-
tal trees and shrubs have not yet matured and consequently are
more subject to damage from early freezes. Since the ability
of trees and shrubs to withstand low temperatures is greatly
influenced by the maturity of the wood, trees and shrubs fed
with excessive amounts of nitrogen fertilizer, resulting in
prolonged growth in the fall, are most commonly the victims of
winter injury. Trees and shrubs frequently suffer severely dur-
ing the winter despite their dormant condition. Their winter
hardiness is influenced by drainage, location, natural protec-
tion, species of tree and character of the root system as well
as by the combination of unfavorable weather conditions. Pine
roots are most likely to freeze in poorly drained soils. The
effects of frozen roots are seldom seen until the following
summer, when damaged trees may wilt and die. Injury to roots
occurs most commonly during winters of little snowfall or in
soils bare of small plants and other vegetation.

PURDUE UNIVERSITY Agricultural Extension Service, Lafayette, Indiana
Department of Botany and Plant Pathology, Life Science Building