Dogwood leaves turn yellow when there is an environmental factor causing the tree stress. If even one aspect is lacking, the tree can succumb to this stress. You can improve the lifespan and overall health of the tree by correctly and quickly identifying the stressor and fixing it.
The most common causes of dogwood tree leaves turning yellow are insects and diseases, leaf scorch, and chlorosis.
In this article, we will discuss these causes of dogwood leaf yellowing and how to remedy each one.
Why are my dogwood tree’s leaves turning yellow?
Insects and diseases
When a dogwood tree is stressed for any reason, it becomes more susceptible to pathogens and pests. The more insects or diseases invade the tree, the more it will deteriorate and ultimately succumb to its invaders.
The most common insects that attack and damage dogwood trees are dogwood club-gall midges, dogwood borers and twig borers.
Diseases that affect dogwood trees include spot anthracnose and powdery mildew. Both these diseases are caused by fungi. They infect dogwood trees that are not properly cared for or are in living conditions that are not ideal.
Leaf scorch
Dogwood leaf scorch is one of the most common problems growers encounter with this plant. This is indicative of a tree that is suffering water stress. A dogwood tree that does not get enough water will have dry leaves with yellowing or browning edges. The leaves will completely dry out and fall off one by one.
You can prevent water stress and leaf scorch by keeping the tree well irrigated. This is important because dogwood trees have shallow roots so they are easily affected by drought. Younger trees are more fragile while older, more established dogwood trees can withstand drought better.
Chlorosis
Chlorosis is a condition in which plants and trees are unable to absorb the nutrients and minerals they need to make chlorophyll. Less chlorophyll means the plant is unable to perform photosynthesis properly, compromising its ability to nourish itself and remain healthy. The leaves on the tree will turn yellow and its growth will become stunted.
Several factors may contribute to chlorosis. These include nutrient deficiencies, structural damage to roots, compacted soil, poor drainage, too much organic matter, pests, and even herbicide use.
Chlorosis damages dogwood trees by further stressing the tree, depleting its energy stores, turning the leaves yellow, stunting the growth and making it susceptible to both disease and pests.
What does a dogwood tree with chlorosis look like?
The most obvious sign of chlorosis is the yellowing of leaves, but keep in mind this can also be caused by conditions other than chlorosis.
The most common deficiency to cause chlorosis is iron deficiency. Iron chlorosis is interveinal, meaning that the leaf yellowing happens in the leaf tissue between the veins, while the leaf veins remain green. This kind of leaf discoloration is directly attributed to an iron deficiency.
How does a dogwood tree become iron deficient?
You may think that the reason for iron deficiency is that the soil has been depleted of iron, but this is rarely the case. The problem in iron chlorosis is more often the tree’s inability to absorb iron from the soil despite there being plenty of iron available. This happens when the soil pH is too high.
Soil pH is important in determining the availability of nutrients to the tree. If the soil is too acidic or too alkaline, this can affect the solubility of the nutrients in the water. If the nutrients are not soluble in water, the tree’s roots will not be able to take them up.
Iron, specifically, is not soluble when the soil is too alkaline, making it impossible for the dogwood tree’s roots to absorb it, leading to iron deficiency and chlorosis.
Are there other nutrient deficiencies that can cause yellowing leaves in dogwood trees?
A lack of potassium can appear as yellowing of leaves, as well as the curling and scorching of the leaves’ edges.
Magnesium deficiency can also affect the tissue between the veins of each leaf. It will turn the leaves more orange than yellow.
A lack of nitrogen affects older leaves more than younger leaves. This is because a tree will instinctively choose to save the remainder of its depleting resources, such as nitrogen, for its younger leaves to support new growth. This causes the more mature leaves to turn yellow or even brown, and then fall off.
Manganese, sulfur and zinc deficiencies in dogwood trees also result in leaf yellowing and chlorosis.
Can chlorosis be treated?
Yes, chlorosis can be treated, but these measures are often temporary and need to be repeated every so often to keep the tree healthy. This is because it is very difficult to permanently maintain a specific pH in a large area of ground. Water will move through the soil when it is watered or rained on, frequently washing away considerable amounts of nutrients.
The best advice when growing trees and dealing with possible chlorosis is to try to prevent it from happening in the first place. If the dogwood is native to your part of the country, you should have no problem growing it with the pH of your soil, since that is probably the pH the tree has adapted to.
If you still get yellowing of leaves due to chlorosis, you can apply elemental sulfur to the soil around the tree to help lower the pH. You can also add chelated iron to the soil if the reason for the deficiency is iron depletion and not the soil’s pH. You can try injecting the tree trunks directly with iron sulfate, but make sure you do your research on how to properly go about this process. Lastly, you can try to increase the iron in the tree by spraying the leaves with chelated iron or iron sulfate.
Hiring a professional to check your soil’s pH and having them choose the appropriate treatment for your situation is probably best.
Conclusion
Dogwood tree leaves turn yellow when there is an environmental factor causing the tree stress. The yellowing can be an indication of a condition that is not so serious, but it can also be caused by something that could potentially affect the overall health of the tree. Identifying the exact cause of the discoloration can be tricky since yellowing leaves are a broad symptom, but once you figure it out, managing the problem becomes easier.
The most common causes of yellowing dogwood leaves are insects and disease, leaf scorch, and chlorosis.
Image: istockphoto.com / RussieseO