Dieback and decline of shade trees
and shrubs
Figure
1
A declining tree showing the typical symptoms of branch dieback and yellowed foliage.
Tree and shrub decline is a progressive deterioration in the health of a tree
or shrub that is attributed to a combination of factors. These may include environmental
stresses such as extremes in temperature or moisture, site problems such as soil
compaction, extremes in soil pH, poor soil texture for plant requirements, mechanical
injuries to trunk or roots, insect infestations and diseases such as defoliating
leaf diseases, root rots and wilt diseases. While each of these factors alone
may not be that detrimental to the plant, in combination they may cause the decline
and death of the plant. The plant, in order to compensate for this stress, will
decrease the amount of top growth to restore the delicate balance between the
branches and roots.
Primary
hosts in Missouri
Sugar maples and many species of oaks are commonly affected, but other trees
and shrubs may also decline. No plant species is completely immune to the problem.
Figure 2
Healthy trees will have 4 to 8 inches of twig growth each year. Twig
growth less than this may indicate that the tree is under stress.
Symptoms
and diagnosis
There is an overall loss of vigor. See figure 1. Early fall
coloration of leaves, late leafing in spring, production of foliage in clumps,
decrease in twig growth (See figure 2), heavy seed crop production,
and twig dieback are all symptoms. These visible symptoms may not occur until
the tree or shrub is severely stressed. A declining plant will also be more susceptible
to other disease and insect problems.
Integrated
management strategies
Prevention and early detection are the key to keeping trees and shrubs healthy.
Plant in favorable environments and avoid stresses. Keep soil pH mildly acidic
for oaks. Avoid unnecessary injury. Water deeply during dry periods. Mulch over
the root system to maintain an adequate level of soil moisture and to promote
root growth. Once the plant is in a state of decline, it will be necessary to
restore the natural balance of roots and shoots by pruning 10 to 20 percent live
branches as well as all dead and dying branches. Use fertilizers high in phosphorus
and low in nitrogen to stimulate root growth. Prevent serious recurrent defoliating
disease with fungicide treatments and treat serious insect and mite infestations.
Updated 6/8/09