Water Trees in a Wide Swath
By Ron Honig
Throughout this brutal summer of high winds and hot, dry conditions, our three Extension offices in the Wild West District received numerous calls related to tree problems, particularly in shelterbelts.
We believe most of these problems are related to drought and other environmental stresses such as winter freeze injury and dehydration injury from sandblasting and high winds. Environmental stress is cumulative. Trees can become weak over a period of years when conditions exist such as repeated drought cycles, severe winter temperatures, disease or insect attacks, and iron chlorosis due to poor soil chemistry.
We received several requests for inspections of pine trees showing brown needles and branches as well as general scorching of the needle tips. Inspection and testing at the K-State plant diagnostic lab in Manhattan showed no disease pathogens present on the samples submitted for testing.
We also received numerous inquiries related to Eastern Redcedar trees and related junipers with yellow to orange needles on the interior of branches. Again, juniper samples submitted to K-State’s diagnostic lab for examination showed no signs of disease problems, leading us to conclude the injury is related to drought stress.
Following the severe drought of 2011 and 2012, K-State’s horticulture department documented a large increase in the death of blue spruce trees, however pines and eastern redcedars also were noted to have suffered significant losses across the state following that long dry period.
We know, of course, that when settlers arrived in southwest Kansas there were very few trees that could be considered native. We have brought tree species into this semi-arid environment that would never be expected to survive in this region without intense management on the part of the landowners. The most limiting factor naturally being moisture.
Most frustrating to property owners I visit with is seeing environmental injury to their shelterbelt and landscape trees despite trying to provide a consistent water supply through use of a drip irrigation system or hand-watering.
One situation we see again and again is the use of a drip irrigation system with an emitter positioned at the base of the tree’s trunk. This system is usually originally designed when the tree row was planted and the trees were small. At that time the tree’s root system was small and entirely positioned under the water emitter.
As the tree flourished and grew, the root system expanded laterally well beyond the tree’s trunk and the emitter on the irrigation hose. Under sufficient growing conditions those expanding roots survived and supported the tree’s increasing size. Under poor growing conditions, those same roots died back if they were not in moist enough soil to maintain the tiny root hairs that are responsible for absorbing water into the tree’s root system. As roots die back, the tree loses the full ability to support its increased size. This reduction in roots however, may not be apparent until the lack of roots becomes too large of an obstacle for the tree to maintain its load of foliage, whether it be leaves or evergreen needles.
Usually a stressed tree will green up initially, and then in the late-spring or early-summer, we notice a rapid decline in the tree’s health.
Under good soil and growing conditions, a 20-year-old tree can send roots out in all directions well past the tree’s “dripline”, meaning the outer edge of the leaf or needle canopy. Without precipitation to feed those wide-ranging roots, the single irrigation emitter can not possibly wet a large enough area to supply that tree’s water demands.
One impulse is to increase the size of the orifice in the emitter or to simply leave the water turned on for a longer length of time. The pit fall to this remedy is that water has a limited lateral movement in our western Kansas soils and water is likely to move downward in the soil profile easier than it will move side-ways. Water that moves downward past the tree’s roots without being absorbed by the tree is wasted for the most part. If your irrigation system is already providing enough water from its emitter to water below the roots, increasing the orifice size or the run time, will not benefit the tree and may possibly damage the tree’s roots by suffocation if roots are allowed to remain in water-saturated soil for too long of period.
We know trees are revered for exchanging carbon dioxide into oxygen, but the root system must have oxygen to survive. Over-watering can kill off roots as easily as a drought period. Adding an additional water line further out from the tree’s trunk to reach those long roots can be an answer to the problem, as well as simply adding additional emitters between trees or switching to a sprinkler system to spread irrigation water over a larger area.
We also must remember that during dry periods our shelterbelt trees are competing with each other for moisture. Those closely-planted trees have roots that are crisscrossing under each other and fighting to absorb as much moisture as possible to survive.
K-State recommends watering to a depth of 12 to 18 inches, if possible. Though this will not reach all the roots of a tree, it will reach the majority of them. Trees normally have at least 80 percent of their roots in the top foot of soil. Shrubs should be watered every week to a depth of 8 to 12 inches. Check depth of watering by pushing a wooden dowel or metal rod into the soil. It will stop when it hits dry soil.
