Yellow leaves in summer is a sign
Often during the summer season we see trees and shrubs that have a yellow coloring. In many cases they are pretty and are supposed to be that way dependent on the cultivar and species. Common trees and shrubs that produce yellow leaves are the sunburst honey locust, the golden ninebark, American elderberry, dwarf goldenlocks elder, mock orange and the golden alder. These are used for ornamental purposes in the garden for a variation in foliage color for the landscape.
There are other trees that get yellow leaves during the summer that are not supposed to get them such as silver maple, quaking Aspen, weeping birch, white birch and river birch. When these selections develop yellow leaves, it is usually due to an issue with its growing conditions. It could be an insect problem, a fungus, a result of drought or flooding, but oftentimes in our area it is due to an issue called iron chlorosis.
The tell-tale symptoms of this condition are the yellowing of the leaves either in sections or in the entire tree. The leaves will become pale yellow to white in some cases, with deep green veins running through them. After a period of time, the very pale leaves can become scorched in the late heat of summer and turn brown and fall to the ground. If this condition persists, branches and large limbs can die. In extreme cases the tree can eventually die also due to long-term stress.
Normal leaves are green because they are filled with chlorophyll, which aids in the production of sugars and energy for the tree. When this chlorophyll exits the leaves, they become yellow, halt the energy production and begin to cause stress for the plant. This is caused by the trees inability to acquire the needed form of iron in the soils as they are unavailable to do for various reasons, the main reason being a high soil PH in excess of 6.5. In our region of clay-based soils, there is high alkalinity and high PH, thus making it prime conditions for chlorosis.
If the yellowing begins on a young tree in the yard year after year, the best prevention is to remove the tree and replace it with a less susceptible species or a native plant. Many of the ones that become chlorotic are non-native to our region.
If the chlorosis occurs on a valuable tree in the landscape or one that is quite large, there are other treatment options available. Three common treatments are soil amendments, foliar sprays and trunk injections. Sometimes one type of treatment will help amend the problem and other times a mix of the options.
Soil amendments means that treatment through the soil is the route of action. One way is to apply elemental sulfur and ferrous sulfate, or iron. For large trees, a solution is to bore numerous holes directly beneath the drip line of the tree about 12 to 18 inches deep and 2 feet apart. Of course, when boring that far down, you will want to make sure you are not going to come in contact with any underground utilities, so plan accordingly. After making the bores, fill the holes with a mixture of equal parts elemental sulfur and iron sulfate to about 4 inches from the top of the bore holes. Fill the remaining 4 inches with soil to cap it off. Over time, this reacts within the soil to create a more acid base, thus making iron more available for the tree to access. This is the most inexpensive option to treat your trees and shrubs.
Foliar sprays are liquids of iron chelates that are sprayed directly on the foliage of the tree or shrub. It remedies the condition within days of application. In minor cases, this is an inexpensive way to remedy the problem. In more severe cares, this application alone will act as a Band-Aid fix to a soil issue, thus will work better when used along with soil bore treatments. One drawback of this type of treatment is on large trees where one is unable to access the higher portions and sometimes it can get applied unevenly.
The final option is trunk injections. It sounds more complicated, and it is, along with the increased expense. Liquids and dry solutions can be directly injected or implanted in the lower trunk of the tree for immediate access within the main living tissue to be transferred to the branches and canopy. Capsules of dry material can be drilled into the lower trunk and slowly absorb into the tree. This is an invasive process, so one will not want to repeat this application any more than a few years apart as you do not want to create open wounds for insects or bacteria to enter the tree. Liquid iron can also be injected into the base of the trunk with a tool that resembles a hypodermic needle. It leaves a smaller wound within the tree and has had very good success rates. The key with this treatment is to not apply it any more than every two to three years to minimize the injury to the trunk that may occur.
As with anything in the landscape, there may be challenges you are faced with in which a remedy or treatment may be necessary to correct. If you are unsure of what you are dealing with, contact a certified arborist or the city forester for further diagnosis. Once you know what you are dealing with, the solution can sometimes be an easy choice.
If you see yellowing appearing in your trees during this time of year, take a closer look and see if it is due to the dry conditions of late summer or if it is actually iron chlorosis that needs to be treated. A healthy tree or shrub is obviously going to be a happy one.