Chartreuse is not usually the first color that comes to mind when describing tree leaves. This bright yellow-green color may be eye-catching, but it can also be a sign that something is wrong. If your trees are looking more chartreuse than dark green this summer, chlorosis may be the culprit.
Chlorosis is a general term used to describe leaves or needles that develop an abnormally light green or yellow color. One of the most common forms seen in Nebraska is iron chlorosis. Trees affected by iron chlorosis often have leaves that are yellow or pale green while the veins remain dark green. As the condition worsens, leaf edges may turn brown, branches may begin to die back, and severely affected trees can decline over time.
The most common cause of chlorosis in our area is not a lack of iron in the soil. In fact, Nebraska soils often contain plenty of iron. The problem is that our naturally high-pH soils can make iron unavailable for plant uptake. The iron is present, but the tree simply cannot access it.
Other factors can contribute to chlorosis as well. Wet or compacted soils, root damage, excessive nitrogen or phosphorus levels, and deficiencies of other micronutrients such as manganese can all interfere with a tree's ability to absorb nutrients.
Some tree species are especially susceptible to iron chlorosis. Common examples include silver maple, red maple, Freeman maple, pin oak, crabapple, pear, birch, and baldcypress. While other species may occasionally show symptoms, these trees tend to be the most frequently affected.
Fortunately, there are several treatment options available.
For young trees with severe chlorosis, tree replacement may sometimes be the most practical solution. Selecting a tree species that is better adapted to our soil conditions can save time, money, and frustration in the long run.
One treatment option is applying elemental sulfur around the tree. Sulfur can gradually lower soil pH, making iron more available to plant roots. This method is relatively inexpensive, but patience is required. It may take one to two years before noticeable improvements occur.
Another option is applying iron chelate products to the soil. Look for products containing FeEDDHA, a form of iron that remains available in high-pH soils. These products are mixed with water and applied around the root zone. While they can provide relatively quick results, treatments often need to be repeated annually and can become costly for larger trees.
Iron can also be applied directly into the tree through trunk injections or iron implants. These treatments typically provide results that last one to three years. However, they require drilling into the trunk, creating wounds that the tree must seal. Repeated treatments over many years may cause additional stress. In Nebraska, trunk injections must be performed by a licensed pesticide applicator, which can increase treatment costs.
The timing of treatment is also important. Spring and fall are generally the best times to address chlorosis. Treatments made during the heat of summer are often less effective because stressed trees may not absorb nutrients efficiently.
Another long-term management strategy is the Whitcomb Method. This technique involves drilling a grid of holes beneath the tree canopy and filling them with sulfur, a complete fertilizer, iron, and micronutrients. While labor-intensive initially, it can provide long-lasting improvements for severely chlorotic trees.
One treatment that should be avoided is the use of iron nails, iron shavings, or other pieces of metal buried around the tree. Despite their popularity in gardening folklore, these methods have not been shown to effectively treat iron chlorosis.
If your trees are showing off chartreuse leaves this summer, don't ignore the warning signs. Proper diagnosis and treatment can help restore healthy green foliage and keep trees thriving for years to come.