Drought is usually defined as prolonged dry periods that can cause damage to tree, plants and other crops. Drought, or water deficits in trees cause them injury, ranging from symptoms of wilting of leaves to total plant death.

Wilting of the leaves in hardwood trees can be temporary, or permanent, depending on the length of time water is unavailable. Temporary wilting can be seen as leaves drooping during the day. At night the tree will rehydrate and recover from temporary wilting. If the tree does not recover during the overnight period temporary wilting can become permanent wilting. Permanently wilted trees plants may recover when water is added to the soil, but prolonged permanent wilting usually kills most species of plants.

Conifer trees, especially pine trees, usually don't "wilt" from drought stress. During very dry periods, the second year needles (located away from the tips of the branches) will turn yellow and begin to drop from the tree prematurely. This is usually a sign of water deficit stress. If the needles on a pine tree turn from yellow to red, the tree is severe, and usually dies.

Sometimes, it is tricky to determine if a tree has died from drought stress or has simply become dormant and appears to be dead. Try this simple test to help determine if a drought-stressed tree is alive or possibly dead. Use your fingernail to scrape a small section of bark from a small twig or branch within reach. If the tissue under the bark is green and moist, the tree may still be alive. To be absolutely sure the tree is not dead, wait until the next spring to see if it sprouts a new crop of leaves.