| Leaf scorch may occur on any species of tree or
shrub as well as herbaceous plants. It is a widespread noninfectious disease or
disorder. Scorch most often occurs following
prolonged periods of dry, windy weather or bright
sunshine when the roots are unable to supply water
to the foliage as rapidly as it is lost by transpiration
from the leaves. Unfavorable locations, such as
sandy or gravelly soil, near obstructions or pavement
that restrict root growth, or exposed windy slopes
usually promote scorch. Anything that affects the
plant’s ability to take up water, including insect and
disease problems, can result in leaf scorch.
Herbicides and pesticides may also contribute to
scorch. Do not spray on windy days to eliminate
drift problems and do not allow mist to settle onto
trees.
In mild cases of leaf scorch, the leaves remain
attached, and little damage results. In more severe
cases, plants may drop many of their leaves
prematurely, although such plants do not die. Where
leaf scorch occurs each year, such annual stress will
gradually weaken the plant, making it more
susceptible to insects and diseases.
Symptoms and Diagnosis
Browning of leaf margins and/or yellowing or
darkening of the areas between the main leaf veins
are symptoms of leaf scorch. Due to environmental
causes, leaves may dry, turn brown, and become
brittle. Look for damage to trees and shrubs on the upper
portion on the sunny, southern side and on the
windy side. Premature dropping of leaves and twig
dieback may occur during the late summer.
Symptoms usually appear after drying winds in
conjunction with periods of hot, dry weather.
Leaf scorch on narrow leaf evergreens appears as
brown or purple brown discoloration of the needle
tips. If unfavorable conditions become more severe,
browning of needles increases. This should not be
confused with the browning and shedding of older
interior needles. Scorch may result from hot, dry
weather in summer or from strong, dry winter winds
when the ground is frozen. Symptoms may not
become apparent for a month or more after the
initial injury.
Winter leaf scorch in evergreen plants usually
appears as two long, brown areas paralleling the
main leaf vein.
Life Cycle
Although plants can experience scorch with no
insects or disease pathogens involved, insect and
disease damage can also affect the plant’s uptake of
water. In some cases, insect damage such as
leafhopper (hopper burn) or specific scorch diseases
caused by fungi or bacteria can produce similar
symptoms. Scorch can also reduce the health of a
plant making it more susceptible to attack by insects
and diseases.
Integrated Pest Management Strategies
1.Water when needed and maintain plant vigor.
Plant in a fertile, well-drained soil at the same depth
the plants grew in at the nursery and with an
adequate supply of organic matter. Soil should be
moist to a depth of 10 to 12 inches after a thorough
watering. This should be done about once weekly. It
is very important for the trees, especially broadleaf
and needled evergreens, to be well watered going
into the winter period. Water during this period if
seasonal rains are not adequate or during the winter
when the soil is not frozen. Annuals and perennials require more frequent watering than most trees and shrubs.
2. Fertilize. Fertilize plants in early spring based on
a soil test and the directions printed on the
fertilizer container. Nitrogen should be applied
annually based on the area to be fertilized, the
type of plant, and the diameter of the trunk. Do
not fertilize with nitrogen in the late fall as it may
cause new soft growth easily damaged by
cold weather.
3. Compaction. If a tree's root system has been injured
by construction or other means of compaction or
if it is restrained by either sidewalks or retaining
walls, it may need to be pruned to balance
the top with the root system. Do not top but
selectively prune to obtain this balance.
4. Mulch. Organic mulches (pine needles, wood
chips, composted leaves, pine bark, cypress
mulch) can help retain moisture during the
summer and fall droughts. In the winter this mulch
prevents the alternate freezing and thawing of the
soil. Mulch will also cool the soil in summer.
5. Screens. Screens may be used to protect trees and
plants in areas exposed to wind and sun, but it is
best not to plant tender plants in these exposures.
6. Exposure. Other factors which can result in
scorch are excessive fertilizer, deicing salt,
herbicide, dog urine, trash fires, leaking sewer or
gas mains, girdling roots or strangling wires,
vehicle exhaust, and heat reflected from
buildings. Elimination of the exposure to these
elements is the only correction.
7. Physical hazards. Avoid root injury when digging
near trees and shrubs. Care should be taken to
not injure the bark and roots when using
lawnmowers, weed whips, and edging tools. | 
