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Recognizing Drought Injury
Symptoms on Plants
Mary Small
Extension Agent, Urban IPM
Jefferson County
An overview:
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 plant’s 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 over watering. 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 yellow-green).
Click on image to enlarge
- Tree canopy may be thin. (Can also be due to
insect, disease.)
Click on image to enlarge
- 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 drought event.
- "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.
Click on image to enlarge
- 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.
- Wood or bark cracks.
- Stems and twigs die, with the outermost and
upper ones dying first.
- Entire plants may die, as the result of root
death from dehydration.
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.
Click on image to enlarge
- Evergreen needles brown from the tip downward.
- Evergreen needles turn yellow, red or
red-purple.
Click on image to enlarge
- 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 drops early.
- 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 decreased resistance.
Click on image to enlarge
- Presence of certain twig beetles and borers,
which are attracted to drought-stressed plants. Drought decreases a plant’s
resistance to these pests.
Click on image to enlarge
Additional Lawn Symptoms:
Click on image to enlarge
- 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 storage.
- 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 exposures).
- Stress-related diseases such as Aschochyta
leaf blight, Necrotic ring spot and Dollar Spot may develop.
June 2002
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