Lack of moisture is the most common stress encountered in landscapes. When drought conditions persist for months or even years, a plant's health and survival is severely impacted. All types of trees and shrubs are susceptible to these conditions, though new plantings that have not become established and very old plants will be most affected.
The first symptoms of drought are usually evident on the leaves or needles. Wilting, defoliation, discoloration, and browning of leaf margins or needles are common signs. Dieback and crown thinning follow along with restricted growth of new shoots and foliage. The severity of symptoms depends on many factors such as the species, soil conditions, and duration of drought.
Drought reduces the plant's ability to produce food, restricts ability to absorb nutrients, and limits growth. That means it's hard for plants to fully recover from drought, sometimes requiring several years. This makes life very difficult for trees and shrubs and they become more susceptible to certain pest problems like boring insects as well as stem and root disease. These secondary invaders can lead to the ultimate decline and death of the plant.
During droughts, plants should be monitored closely for pest problems. Proper irrigation is also critical with water applied to the root zone and not directly on the trunk. Mulch can also help conserve soil moisture and reduce competition for water. Finally, pruning of any dead or dying limbs and regular fertilization will help minimize the effects of drought. Please note that fertilizer should be applied only after drought has ended and soils are recharged by rainfall.
If you live in a region that is prone to these extreme weather conditions, planting drought-resistant trees and shrubs is also an excellent idea.