Red Oak Leaves Are Turning Yellow in the Summer

Oak Wilt

• Red oak leaves turning yellow in the summer could be a sign that the tree is suffering from oak wilt, a fungal disease brought on by the pathogen Ceratocystis fagacearum. When infected, the foliage of the tree begins to die from the top downward, with the leaves wilting and turning a bronze or yellowish color along the edges. As the disease progresses, the leaves turn completely yellow and fall to the ground; sometimes healthier, green leaves fall too.

Wilt Management

• Oak wilt is extremely lethal and the red oak is especially susceptible to the problem. It often dies within one year of contracting the disease, although the tree is capable of surviving for up to two years. Animals like squirrels, and even devices like pruning shears, spread the pathogen from one tree to another. It also moves between the root systems of trees with intertwined roots. An afflicted red oak should be removed from the environment immediately to protect adjacent trees.

Iron Chlorosis

• Oaks of all species, including the red oak, are likely to experience a yellowing of their leaves if the soil in which they are planted is lacking in iron. This condition is known as iron chlorosis and is indicated by a near total yellowing of the margins of the oak leaf, while the veins retain their green. It normally appears most severe on new foliage at the tips of a branch. Eventually, the leaves will curl, dry and fall away.

Damage

• If chlorosis continues for several years, large limbs or the entire tree can die. The lack of iron is detrimental to the leave's ability to conduct photosynthesis, the process by which the foliage produces energy and the tree retains vigor.

  A lack of nitrogen in the soil can also encourage the yellowing of leaves. This problem tends to appear first in older leaves, rather than the newer leaves that suffer initially when chlorosis is the problem.