Small, Colorado State University
Cooperative Extension Agent, Urban IPM
Recognizing Drought Injury
Symptoms on Plants
Drought stress occurs when plant roots are not absorbing
enough water for their needs. There are many causes for drought stress. The obvious one is
insufficient moisture. However, sufficient moisture may be present but plant roots are not
functioning properly to absorb it. There may be just enough present for the plant to
maintain itself, but no extra available for growth. In some cases, plants that are
over-watered suffer drought stress symptoms. Over-watering drives oxygen out of the soil,
which is needed by plant roots for proper functioning. If there is insufficient oxygen,
roots die, just as they do when there is insufficient water.
Drought may be of two kinds: short-term and long-term. An
example of a short-term drought is the length of a growing season. A long-term drought
lasts more than one growing season. While a short-term can damage plants, the long-term
droughts are more harmful due to the chronic moisture stress.
Symptoms are the plants reaction to stress and
provide clues during diagnosis. Following are some common symptoms of drought stress. Be
aware, however, that symptoms may mimic. Many of these symptoms may also be the result of
other causes such as compacted soil, mechanical root injury, freezes, improper pesticide
use and overwatering. Consider weather events and cultural practices along with the
symptoms when making a diagnosis.
Symptoms found on entire plant:
The pattern of plant damage or death occurs from the top of
the plant down and from the outside of the plant inward.
- Plants wilt. One of the first symptoms of drought-stressed
plants is the loss of turgidity. Plants or plant parts become limp and droopy.
- Plants show a decrease in growth or have no growth, both in
girth and in length. A way to verify this on woody plants is to check the length of the
growth increments, the amount of growth produced in each season. Beginning at the tip of a
twig, move along the twig toward the trunk. Look for the first set of
"wrinkles". The distance from the tip to the first set of wrinkles shows the
amount of growth produced during the most recent growing season. Look for the next set of
wrinkles. This show s the amount of growth produced by the plant during the previous
season. Continue checking the length of the increments. If they are short or getting
shorter, this can indicate a decline in root function. (Recently transplanted trees may
have short growth increments until the root systems re-establish.)
- Plants or sections of them, appear chlorotic (yellow or
- Tree canopy may be thin. (Can also be due to insect,
- Plants may leaf out, then die later in the growing season,
a result of depleted food reserves. This may occur during or even a few years after, a
- "Winter-kill" may occur. A reduction in hardiness
develops as the result of decreased food production, movement and storage that occurs
during a drought.
- Gummy exudates appear on twigs, branches and trunks.
- Suckers develop on branches and trunk.
- Heavy seed production. This may also be a normal plant
response to certain weather conditions. Some plants normally produce large amounts of seed
every few years.
- Stems and twigs die, with the outermost and upper ones
- Entire plants may die, as the result of root death from
Symptoms found on leaves:
Leaves are smaller than normal.
- Deciduous leaves turn brown from the outside edges inward
and in between the veins ("scorch"). This symptom occurs because these areas
naturally have the least amount of moisture in the leaf
- Evergreen needles brown from the tip downward.
- Evergreen needles turn yellow, red or red-purple.
- Leaves roll up and/or are misshapen.
- Leaves drop prematurely. They may or may not turn color
prematurely before dropping.
- Leaves remain attached to tree, even though brown.
- Leaves are dull in appearance rather than shiny.
- Leaves may turn blue-green.
Flower and Fruit Symptoms:
- Flowers fail to open properly.
- The flowering period is shorter than normal.
- Fruit and seed production may be reduced or absent.
Pest Problems related to drought:
Moderate to large amount of spider mites found. Spider
mites are attracted to, and proliferate on, drought-stressed plants.
- Canker development on trunks, twigs and branches. Disease
organisms are better able to successfully attack drought-stressed plants because of their
- Presence of certain twig beetles and borers, which are
attracted to drought-stressed plants. Drought decreases a plants resistance to these
Additional Lawn Symptoms:
- Turf browns, in entire patches or in spots. Spotty browning
can be the result of localized dry spots and/or improper sprinkler function.
- Thinning lawns as a result of decreased food production and
- Appearance of more lawn weeds, a result of lawn thinning.
This provides physical space for weed seed germination and growth. Some weeds are more
heat-tolerant than bluegrass and will successfully colonize areas where bluegrass has a
difficult time competing (i.e., along driveways, sidewalks and streets, south and west
- Stress-related diseases
such as Aschochyta leaf blight, Necrotic ring spot and Dollar Spot may develop.
Photos: Judy Sedbrook
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