Tree Diseases - Drought Stress
Extended droughts can cause decline and death on young and mature trees. Even large trees more than one hundred years old can decline. Foliage on drought stressed trees thins and drops beginning at the top center part of the canopy. This is a natural way for the tree to reduce water loss from transpiring leaves. Reduce the amount of leaves reduce water loss. This can be largely prevented with timely application of irrigation, and appropriate soil management. It is better to apply water preventively before the canopy begins loosing foliage than to wait until these symptoms are advanced. Large shade trees can go through 80-100 gallons a day if weather conditions are right.
Apply water across the soil surface and let it soak into the soil. Surface soaking allows tree roots more chances to absorb any water, helps maintain soil health, and helps maintain essential element cycling and transformations in the soil.
If you can duplicate a rainfall of about 2 inches a week, you are doing great. If Mother Nature provides enough precipitation to wet the soil 2 to 3 feet deep, don't apply additional water. However, if natural rainfall falls short of a full soaking, apply only enough additional water to wet the soil 2 to 3 feet deep.
The best time to water is at night from 10 p.m. to 8 a.m. Trees relieve water deficits (refill) during the nighttime hours. Watering at night allows effective use of applied water and less evaporative loss, assuring more water moves into the soil and tree. The next best time to water is in late afternoon when the foliage is dry and evaporation potential is not at its daily peak.
Plan to water newly planted trees each summer for the three years after planting. Once past this establishment window, the tree should be able to survive on its own without supplemental water.
Evergreen trees, however, always will lose water during the dormant season. These trees should be watered during winter droughts. Because temperatures are low and relative humidity is typically high, much less water is required in the dormant season, but water still is needed. Do not water when the soil surface is less than 40 degrees F.
Manually, the best ways to water trees are by soaker hose or trickle (drip) irrigation, which you turn on and off. Even a garden hose, moved often, can provide a good soil soaking. Take care to water the surface beneath the tree's canopy, but not the tree's canopy. Foliage that is watered can be sunscalded or could develop fungal foliage disorders.
Newly planted trees are the most susceptible to water stress and should be monitored closely. Many times these trees have lost a percentage of their root system in the digging process and are not very efficient with water uptake. Concentrate on watering just the basal root system of new trees and check often with a soil probe to inspect water dispersal.
If you are using a sprinkler system, you can estimate this amount of water by placing several small containers under the canopy of your trees. When the average depth in the containers equals 2 inches, you are done with that tree. In addition, you can probe the soil to a depth of 6 to 8 inches when you are done watering to make sure the soil is saturated to that depth.
When should I water?