Treating Sick Dogwood Trees: Reasons For A Dogwood Tree With Yellow Leaves
Autumn foliage aside, yellow leaves on a tree generally doesn’t signal health and vitality. The flowering dogwood tree (Cornus florida) is no exception. If you see your dogwood tree leaves turning yellow during the growing season, the tree is likely suffering from a pest, disease or deficiency. Read on to find out why your dogwood has yellow leaves.
Avoiding Sick Dogwood Trees
When delicate blossoms open on your dogwood tree boughs, you know that spring is on the way. This native tree grows wild throughout the eastern states, and it is also a popular ornamental. The small size works well in home gardens and backyards, but improper culture can cause sick dogwood trees.
The best defense against pests or diseases attacking your dogwood is to provide appropriate care for your tree. This is easier when you understand that dogwoods are understory trees in the wild, growing in shade on organically rich soil. You need to provide a similar environment.
Dogwood Tree with Yellow Leaves – Borer Attacks
If your tree canopy dies back or the leaves turn fall colors prematurely, it may indicate a dogwood borer attack. This insect is the most common pest of the cultivated dogwood.
Adult borers are day-flying moths that lay their eggs wounds or fissures in the tree bark. As the insect larva emerge, they bore into the tree, leaving holes and sawdust-like frass as evidence of their presence. Yellow leaves on dogwood trees can be an early sign of an infection.
To prevent a borer attack, plant your dogwood in shade, not direct sun, and provide adequate irrigation to avoid water stress. Don’t weed whack close to the base of the tree or otherwise wound its bark, since wounds provide an entryway for the borers.
Yellow Leaves on Dogwood Trees – Chlorosis
Another possible cause of yellow leaves on dogwood trees is chlorosis. Dogwood trees are susceptible to iron chlorosis, which means that the trees are not uptaking sufficient iron to manufacture chlorophyll, the green pigment in leaves.
You should suspect chlorosis if the yellow first shows up in the area between the leaf veins, leaving the veins green. In more severe cases, the entire leaves turn pale yellow.
To prevent chlorosis in your dogwood tree, check the soil acidity before planting. Dogwoods cannot absorb the iron in the soil if it is too alkaline, that is, if the pH is above 7.5. While you are doing soil testing, check for magnesium, manganese and boron levels as well, since deficiencies in these minerals can also cause chlorosis.
When you see your dogwood tree leaves turning yellow because of chlorosis, make sure you are watering appropriately. Overwatering the tree (or poor drainage) can also cause chlorosis. Likewise, root damage, girdling roots and trunk wounds all make it more difficult for the tree to transport nutrients.
Dogwood Has Yellow Leaves – Other Issues
If your dogwood has yellow leaves, the tree might also suffer from some other disease. For example, leaves with powdery mildew can turn yellow. Identify the disease by the white powder on foliage.
Similarly, scale infection can also cause yellow leaves on dogwood trees. Scales are legless insects that look like small brown bumps on foliage or stems. Kill adults and eggs by spraying horticultural oil in spring.
Signs of Stress in Dogwood Trees
Dogwoods (Cornus florida) are flowering deciduous trees that are planted as specimen, or accent trees, due to their ornamental value throughout all four seasons. Thriving in U.S. Department of Agriculture plant hardiness zones 5 through 9, dogwoods are native to the eastern United States. Without proper cultural care, dogwood trees easily succumb to stress, which makes them a target for further stressors, such as pests and diseases. Improve the health and lifespan of your dogwood tree by regularly checking for signs and symptoms of stress.
Dogwood trees have a naturally attractive rounded shape, so they require little pruning unless needed for aesthetic reasons or to improve their vigor. The best time to prune is in the late fall or winter while the tree is dormant.
Water your dogwood on a regular basis until it is established. Then provide additional water during hot dry spells and mulch to help retain moisture. Keep the mulch pulled back a few inches from the tree trunk.
Be careful when fertilizing a young dogwood tree-many newly planted trees are killed by applying too much fertilizer. For this reason it is often safest to hold off on fertilizing until your tree is in its second season. If you have an established dogwood that you feel would benefit from fertilization, have your soil tested to determine the best course of action. Additionally, fertilizer applied too late in the season can stimulate new growth, making the tree vulnerable to winter damage.
Dogwoods are subject to anthracnose, a fungal disease that causes leaf spotting and twig dieback. Preventive measures include providing good air circulation to keep foliage dry, and watering in the summer during periods of drought. Any diseased twigs and branches should be pruned off.
The most common insect pest is the dogwood borer, whose larvae burrow under the bark of the trunk and limbs. Because newly hatched larvae enter the tree through wounds or broken bark, avoid damage to the bark when doing lawn maintenance or pruning. Infected trees can be treated by spraying with an insecticide.
Ideas for the Yellow Twig in the Landscape
Yellow Twig Dogwood makes a wonderful contrast plant that provides winter interest.
Use in a mixed border, make a hedge of them or plant them as a specimen. They look wonderful as a mass planting, too.
Their fibrous root systems make them excellent choices for erosion control.
They are perfect additions to a woodland or contemporary garden. They attract wildlife and fall color.
Plant them with kerria, astilbe or sedge. You can also mix them with red twig dogwood for a wonderful contrast.
The white berries are a favorite food of many songbirds that will find your garden a wonderful place to visit.
Improving Health and Vigor
Reduce stress and improve the health and vigor of your dogwood tree by providing the very best growing conditions and maintenance. Dogwoods require partial sun, and fertile, well-draining soil. Stick to a regular schedule of pruning and fertilization for a healthy tree with adequate nutrition.
Dogwood trees also have problems when there is not enough sunlight or air flow through the canopy of the tree therefore, pruning is an important part of maintenance. Always remove damaged, broken or diseased limbs. Keep your dogwood tree free from pests and diseases that cause stress by keeping the area beneath the tree clean and free from debris and leaf litter. A fungicide or horticultural oil treatment in the early spring, just before the tree begins to bloom is another way to keep pests and diseases at bay.