Yellowing leaves-Birch, Oak and Maple (Chlorosis)
We’ve noticed many trees showing signs of chlorosis this summer. Our hot, dry weather has made this year quite bad for chlorosis. Common tree species exhibiting chlorosis are pin oak, red maple, white oak, river birch, magnolia, and white pine.
Chlorosis is a yellowing of normally green leaves due to a lack of chlorophyll. Even though the signs of problems are seen on the leaves, the major problem lies underground with the root system. Many factors, singly or in combination, contribute to chlorosis. In southeastern Wisconsin, some of the most common causes among trees and shrubs include nutrient deficiencies related to soil alkalinity (high pH), drought, poor drainage, and compaction of the soil. Common tree species exhibiting chlorosis are pin oak, red maple, white oak, river birch, tulip tree, sweet gum, bald cypress, magnolia, and white pine.
A common sign of chlorosis is yellowing leaves with green veins. (The veins are the last part of the leave to turn yellow.
SYMPTOMS OF CHLOROSIS
Chlorotic plants may only show symptoms on one or two branches, or the whole plant may be affected. The first indication of chlorosis is a paling of the green color of the foliage, followed later in the season by a general yellowing. In mild cases, the leaf tissue is pale green, but leaf veins remain green. In moderate cases, the tissue between leaf veins is bright yellow. In advanced cases, leaf size is stunted and the leaf tissue is pale white to pale yellow. The leaf margins may become scorched or develop brown, angular spots between the veins, and the leaves may wither and drop prematurely. In conifers, an overall yellowing of the needles occurs. If severe, the needles progressively turn brown and drop, and twigs and branches may die back.
CAUSES OF CHLOROSIS
The most common cause of chlorosis is high soil pH level. Most urban soils in southeastern Wisconsin are alkaline with a high pH level, (especially urban soils that have been disturbed by construction). With most plants, the micronutrients iron, manganese, copper, and zinc are most available when the pH is between 5.0 and 6.5; a soil pH range between 6.0 and 6.5 is considered optimal for nutrient availability. Excesses of potassium, magnesium, and phosphorous also contribute to chlorosis. When present in excess, these elements cause some trees, particularly birches oaks and maples, to take up inadequate amounts of the micronutrients iron and manganese. Stressors, such as temperature extremes, drought, poor drainage (which limits soil aeration) or restricted root growth, further limit nutrient uptake in plants sensitive to chlorosis and can make chlorosis dramatically worse.
There are numerous ways to combat chlorosis in trees, and we use a variety of different methods and procedures depending upon the severity of the chlorosis. There is no silver bullet, and often a combination of techniques is used.
- Spraying applications of micronutrients to foliage can provide rather quick green up of the leaves but can be temporary in nature, usually lasting just the season.
- Trunk injections are applied either as micro injections (small concentrated injections) or macro injections (longer lasting dosages mixed in water to provide more thorough uptake in the tree. Trunk injections can have effects that last 2-3 years.
- Soil fertilization treatments produce the best results, but are usually the slowest to respond. Soil fertilization treatments can help change the pH level of the soil over time, and can help create healthier more robust root systems.
Long term solutions:
The most lasting results are obtained by improving the tree’s rooting environment.
- Remove existing grass from under the tree.
- Aerate root system with air spade.
- Apply a one-to-two inch layer of organic compost and/or three-to-four inches of organic mulch. This will reduce weed competition, prevent soil temperature fluctuations during the winter and summer, and help to create more favorable soil conditions for roots to grow.
- Water during dry periods to minimize stress.
If you feel that your tree(s) may have chlorosis or you think something isn't right with your trees, contact Hoppe Tree Service to schedule an inspection by one of our certified arborists.