Oak Tree Diseases

When properly cared for, oak trees can live for decades. They are a symbol of strength and solidity to many people. However, there are some diseases that can topple an oak in a season if they are not addressed immediately and effectively. The best way to keep your oak tree healthy for years to come is to know the signs and symptoms of oak tree diseases so that you can treat them quickly and efficiently when they occur.

Diplodia Canker

Diplodia canker attacks new growth. It rarely tackles branches larger than one inch around, but it can weaken, stunt and deform your tree if left untreated. If your oak tree has diplodia canker, you might first notice that your tree is looking "shabby" due to unequal defoliation and brown leaves. Check the smaller branches on affected limbs, and you will likely see the swollen nodes that indicate the presence of canker problems. Use sterile pruning to remove impacted branches about 4 inches below the canker. Dispose of the tree debris in sealed garbage bags or by burning. This should eradicate the problem, but if it does not, then you can treat the tree with a fungicide as well.


Anthracnose fungus attacks oaks in moist, shaded areas and is spread by the splashing of spores onto different parts of the tree during heavy rains. You will notice browning of leaves in the lower branches, with the veins discoloring first and then the remainder of the leaf. Left unchecked, the fungal infection will spread upward through the tree. Use sterile pruning to remove affected branches and dispose of them so that the spores cannot reinfect the tree. If the weather stays dry, this will probably give your tree time to recover. If the weather is wet, the disease may come back. Simply keep it in check until the weather is dry enough to kill it. In the University of California's "Landscape Notes" newsletter, James Downer, a farm adviser, says thiophanate-methyl sprays have been used to treat this, but weather is the biggest determining factor in the disease progression.

Sudden Oak Death

Sudden oak death first appeared in California in 1995. The U.S. Department of Agriculture reports that as of 2002 the disease was known to occur only in California and Oregon. However, transplants could cause the spread of this disease. Sudden oak death is caused by the fungus Phytophthora ramorum, which kills trees via the fast formation of oozing, infected cankers that quickly defoliate a tree and destroy limbs and branches. Look for swollen, bulging areas that indicate the presence of cankers on stems and branches. Caught in time, it's possible to save the tree through sterile removal of the cankers. However, once dieback begins and the leaves start to yellow and fall throughout the canopy, you should simply remove the tree as quickly as possible to prevent further spread of infection.

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Carole VanSickle has over five years experience working with scientists and creative scholars to promote and explain their work. She is based in Atlanta, Ga., and specializes in scientific, medical and technical writing, SEO and educational content.