Recognizing Drought Injury Symptoms on Plants

Recognizing Drought Injury Symptoms on Plants

By Mary Small, Colorado State University Cooperative Extension Agent, Urban IPM

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 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.

damage occurs from top of plant down (2040 bytes)

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.)

decreasing growth increments (2330 bytes)

Plants or sections of them, appear chlorotic (yellow or yellow-green).

chlorotic sections at top of tree (3178 bytes)

Tree canopy may be thin. (Can also be due to insect, disease.)

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.

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

drought scorch on katsuda tree (2743 bytes)

Evergreen needles brown from the tip downward.

needles turn brown from tip down (3987 bytes)

Evergreen needles turn yellow, red or red-purple.

evergreen needles turned purple (3624 bytes)

Leaves roll up and/or are misshapen.

Leaves drop prematurely. They may or may not turn color prematurely before dropping.

premature leaf drop in July (2429 bytes)

Leaves remain attached to tree, even though brown.

brown leaves remain on tree (2673 bytes)

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.

spider mites on douglas fir (2408 bytes)

Canker development on trunks, twigs and branches. Disease organisms are better able to successfully attack drought-stressed plants because of their decreased resistance.

Presence of certain twig beetles and borers, which are attracted to drought-stressed plants. Drought decreases a plant’s resistance to these pests.

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 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).