Why are the leaves on my tree turning brown in summer?

Thirst is the first suspect. The Virginia Department of Forestry lists the signs of drought as wilting, leaf scorch, browning or yellowing, early fall color, early leaf or needle drop, or dry and dusty soil.^[1] Check the soil first and water deeply if it is dry. If the soil is fine, the pattern of browning points toward a disease or a borer, and that needs a diagnosis rather than a guess.

Start with the pattern

Walk around the tree and note what is brown and where. Browning on leaf tips and edges across the whole crown looks different from one dead branch among green ones. Check the neighbors too: damage across several different kinds of plants in one spot also suggests nonliving factors, such as weather or water.^[3]

Drought and heat

A hot, dry spell is a common cause in summer. Short periods of drought and heat will not harm trees and is quite common in summer months, but extended periods of drought conditions may require deep and frequent watering.^[1]

Do not guess whether the soil is dry. The USDA Forest Service's Tree Owner's Manual says to check the soil moisture at 6 inches below the surface.^[2] If it is dry, water slowly so it soaks in rather than running off. The forestry guide's target is to simulate up to 1 inch of rainfall per week when rain is inadequate during the growing season.^[1] For a tree planted within the last three years, the manual says: "If the soil is dry, provide about 2 gallons of water per diameter inch of the trunk."^[2]

Too much water looks the same

Waterlogged soil produces the same picture from above. Drought and waterlogging produce many of the same symptoms on the aboveground parts of the plant, mainly chlorosis (yellowing leaves), abscission (shedding older leaves), and wilt.^[3] Soil saturated with water for more than 24 hours can prevent roots from getting oxygen.^[2] If the ground under the tree is soggy every time you check, stop watering and look at drainage, downspouts and sprinklers pointed at the trunk.

Mulch can add to the stress. Do not put mulch in contact with the trunk, and then pile mulch only 2 to 3 inches over the roots.^[4] A tall mound against the bark holds moisture where it should not be.

Bacterial leaf scorch

If the browning begins at the leaf edges in midsummer and comes back every year, bacterial leaf scorch is a possibility on susceptible trees. The forestry guide lists American sycamore, mulberry, grape, American elm, sweetgum, boxelder, dogwood, red maple, and sugar maple among the hosts, plus several oaks.^[1] Leaves will start to brown prematurely in midsummer.^[1]

The disease is chronic, and you cannot confirm it by eye. The only way to confirm bacterial leaf scorch is through laboratory tests for the bacteria.^[1] There is no cure, though antibiotic treatments can help prolong the life of the tree.^[1] Water stress can exacerbate symptoms, so irrigate during drought conditions.^[1]

Borers and dieback

Wilting that appears on scattered branches rather than evenly across the tree can mean a borer. On oaks, the two-lined chestnut borer is a stress-driven example: wilted foliage on scattered branches is typically the first symptom followed by branch mortality and then crown decline.^[1] It attacks trees that are already weakened or stressed, which is one more reason to fix watering and mulch.^[1]

On an ash, wilting leaves and thinning crowns can be a sign of emerald ash borer, because as larvae feed underneath the bark, tree foliage wilts and canopy dieback occurs.^[1] If you have an ash, read how to protect ash trees from emerald ash borer in Virginia.

Get a diagnosis

When watering and mulch do not explain it, collect evidence. The Virginia Department of Forestry suggests noting whether there are mushrooms at the base of the tree, exit holes from insects, or spots on the leaves, and taking photos that show the whole plant plus close-ups of the injury.^[6] Send them to your local DOF forester, or send a sample to the Virginia Tech Plant Disease Clinic and Insect ID Lab.^[6] For a fuller walk-through, see how to treat a sick tree.

Stop and call a pro if

• The browning is on a big tree you cannot reach. Anything that needs a ladder, climbing or a chainsaw is arborist work. When to call a certified arborist explains who to hire.
• A single branch or half the crown is dying while the rest is green. That pattern suggests a problem at the roots or in the trunk and should be examined before the branch comes down on its own.
• The trunk is cracked, has fungi or cavities, or the tree has started to lean. The tree may be a hazard to the house, a car or a power line.
• You are thinking of spraying. Virginia law says no person may apply or recommend for use any pesticide commercially without a pesticide business license and the employment of a certified commercial applicator.^[5] An arborist can also tell you whether anything is worth spraying at all.
• A power line is near the branches. Keep ladders, pruners and yourself away and call the utility.

Getting help in Virginia

For what a visit costs, see what an arborist costs in Virginia. Browse more lawn and landscaping answers or tree and shrub health services, or the wider lawn and landscaping directory.

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