Care of trees during drought
When trees suffer from drought they become targets of opportunity for many insects: bronze birch borers on birches, two-lined chestnut borers on oaks, bark beetles on pines, etc. Some insects have developed the ability to detect trees under stress. For example, studies have shown that two-lined chestnut borer adults are able to rapidly and specifically locate stressed oaks in stands containing stressed host species, unstressed host species and nonhosts. The rapidity and specificity of the attack showed that the beetles were able to detect stressed trees from a distance. Two-lined chestnut borer females are attracted to volatiles from stressed white oak trees. Stressed trees also have less energy and resources to defend themselves and to produce "defensive" chemicals once attacked. For example, stressed pine trees may not be able to produce enough resin to pitch out the invading bark beetles.
The best way to care for your trees during drought is to water them. Trees with sufficient water are not as attractive to many of the insect pests. Also they can mobilize more energy to protect themselves if they are attacked. Trees should receive one inch of water per week during the growing season either from rain or watering. One good soaking is better than two or three light sprinklings. Light sprinklings actually benefit your grass more than your trees. Lay the hose on the ground and let it soak into the soil. If using a sprinkler set an empty tin can out so you can measure how much water you apply.
Some other recommendations to help trees stressed by drought include the following:
Also remember to conserve water during a drought. You are using extra water to keep your trees healthy so you need to conserve someplace else. Shut the water off when brushing your teeth or washing dishes. Don't wash the car. Give up baths for the summer. Thinking of taking a shower tonight? Doesn't that sprinkler under your trees look like it would be just as refreshing.....