Why Are Tree Leaves Yellowing and Falling Off in August?

Even though August is still considered summer, many trees in Connecticut are showing early signs of autumn. Tree leaves are turning yellow or brown, and we’re seeing premature leaf drop.

That’s prompted customers to call us with questions about their trees, such as:

• Why are tree leaves turning yellow in summer?
• How do I know what’s causing my trees to yellow and drop leaves?
• Are yellowing tree leaves normal in summer?
• Is it bad for trees if they drop leaves early?
• How can you prevent summer leaf yellowing or leaf drop?

We answer those questions, and more, below.

About Early Leaf Color & Premature Leaf Drop

We normally associate changing leaf color and falling leaves with the seasonal change from summer to autumn. But when we notice these changes happening in summer, it raises concerns.

What should trees look like in late summer?

By the end of summer, both you and your trees might feel a little tired from the long, hot days. You can expect to see occasional drooping or wilting leaves during heat waves or a dry spell.

But when these conditions end, your trees should recover. As temperatures cool, or if you get a good rainstorm or irrigate your trees, you should see improvement in your tree’s appearance within days.

You may see some yellow leaves and some leaf drops in late summer. A few yellow leaves falling in summer doesn’t automatically mean your tree is in trouble. For example, a tree may drop insect-damaged or diseased leaves if they no longer produce food energy for the tree by photosynthesizing.

Some trees also put out new leaf growth all summer. These new, healthy leaves will replace earlier, damaged leaves that drop to the ground.

Look for these eight common symptoms that mean your tree is suffering from pests, disease, or environmental stress and learn what to do about it.

When are yellowing or dropping leaves in summer a problem?

Your tree may be struggling if you see a lot of yellow leaves on your tree and a lot of leaves dropping before autumn arrives. And if most of a tree’s leaves fall off in summer, there’s definitely a problem.

Why do tree leaves yellow or drop in summer?

Below are some common reasons why trees in Connecticut may develop yellow leaves in summer or drop leaves early.

Improper Watering

Yellowing leaves, browning leaves, and leaf drop are all signs of water stress. This can be due to too much water or too little.

Signs of Overwatering – If you’ve been overwatering your trees, you’ll see drooping and yellowing leaves, and more dropped leaves than usual. This happens because a tree’s roots are “drowning” in saturated soil, and leaves can’t expel water fast enough.

Signs of Underwatering – Underwatered or drought-stressed trees will also drop leaves to conserve energy. This is a natural response by many trees as it reduces the amount of energy a tree needs to produce. As a result, the tree enters a type of growing-season dormancy.

• Summer dormancy from severe drought stress can cause all a tree’s leaves to fall.
• In contrast, briefer episodes of drought will cause leaves to turn yellow or brown and look limp and scorched. Partial leaf drop from drought stress is common.

Hot Weather & Heat Waves

High temperatures can do a lot of damage to trees. Irrigation during heat waves helps, but a tree’s whole system struggles with excessive heat. This is because the weather has exceeded the temperature range a tree has evolved to grow in.

When excessive heat damages your tree, you may see:

• drooping yellow leaves throughout the tree’s crown,
• drooping twigs and branches, and
• leaves at the ends of branches may die back.

When leaves are too damaged to survive, they may drop early.

Insect Infestation

Insect pests are active during the long, hot days of summer, and insect populations can explode quickly, causing infestations.

There are many insects that attack trees, in many ways. For example, insects that chew through leaves or suck out sap will damage leaf surfaces and veins. This stops leaves from making food energy and taking up water and nutrients.

When insects kill leaves, or when the nutrients that leaves need to remain green are missing, leaves will turn yellow, wilt, and drop.

Diseases on Your Tree

Like insects, there are lots of leaf diseases that can attack your trees.

Hot, humid summer weather is ideal for fungal growth, and fungal leaf diseases can spread fast. Bacterial leaf diseases, such as fire blight and black spots, are also common in summer, and warm weather and rain help spread them.

As diseased areas on leaves grow, they kill leaf tissue and the leaves can’t make food energy from sunlight. This causes leaves to turn yellow and wilt. Some leaf disease spots develop yellow areas around their edges, so you may see circles or irregular areas of damage with haloes of yellow around them.

Like insect-damaged leaves, leaves damaged and yellowed from disease will often drop early. If your trees are regularly damaged by leaf diseases, a tree evaluation and treatment plan can help control the problem.

Lack of Nutrients or Poor Soil Condition

Trees need a full range of nutrients to remain vigorous and develop healthy, green leaves. When certain nutrients such as iron, nitrogen, or manganese are not available, leaves will become chlorotic (turn yellow).

Which leaves on your tree turn yellow first is a clue to what nutrients are missing. For example:

• iron chlorosis appears on new leaves at the end of branches, while
• nitrogen deficiency affects older leaves first as the tree tries to support new growth.

The only way to know exactly what nutrients your soil is lacking is to perform a soil test.

Many leaves that are suffering from nutrient deficiency but are still alive can regain their healthy green color after proper fertilization.

See the common soil problems in CT, how it affects your trees, what to do about it, when, and how.

Pesticide or Herbicide Damage to Your Trees

Herbicides like glyphosate will not only kill weeds, they will also kill your tree’s leaves. There are over 750 products containing glyphosate for sale in the United States, so check the label of any product you intend to use.  Even if you’re not intending to spray your trees, it’s common for wind-carried spray drift to land on trees.

When herbicides land on your trees (or other plants) or are taken up through their root system, their leaves will turn yellow, wilt, and die. Don’t apply herbicides near tree roots and never spray during windy weather! And if you do accidentally get herbicide on the wrong plant, wash it off at once with water.

Pesticides can also cause your tree’s leaves to turn yellow, droop, and die. This happens when pesticide drifts to non-target trees, when you spray too much pesticide, or if you apply it at the wrong time.

Always follow product directions when applying pesticides. Avoid spraying your trees during very hot and humid weather, or if your trees are already stressed. And of course, before you spray, make sure you’re using a spray designed to treat the problem. Or, better yet, have an arborist diagnose and treat any pest problems on your trees.

Is it bad for trees to have their leaves turn yellow or drop early?

Whether or not leaf yellowing or premature leaf drop is harmful depends on the severity of leaf loss. Trees rely on their leaves to produce food energy for growth, so any loss of leaves reduces the amount of energy a tree can use and store.

Trees build up stores of food energy, so it’s likely that your tree will survive some summer leaf loss by drawing on energy reserves.

The real damage to trees from leaf loss in summer is from repeated, annual leaf loss.

When a tree is repeatedly stressed or damaged, it will deplete its internal energy reserves to stay alive. As a result, its overall vigor will decline. If your trees put out fewer and smaller leaves than normal, they may be struggling from a lack of resources.

How can I tell the difference between tree problems and fall color change?

All trees respond to season-change cues. In late summer the angle and intensity of the sun change and temperatures start to drop as fall approaches.

But trees, and weather, don’t follow our written calendars! So, if summer weather is unseasonably cool or if there’s an early cold snap, you may see leaves change color early. This is normal.

It’s also normal to see a reduced intensity of fall color if we’ve had prolonged summer heat and drought.

When to be concerned – You should be concerned if:

• your trees’ leaves all wilt and turn yellow before the end of summer, or
• a tree drops all its leaves at once.

This can signal that your tree is struggling, and it’s a good idea to have your trees evaluated by an arborist.

What can I do to prevent early leaf drop?

The best way to ensure your trees’ health is to maintain them all year. Make sure that:

• Your trees have nutrient-rich soil
• Your irrigation system supplies enough moisture, and
• You treat insects and diseases early before the damage becomes severe.

Connecticut’s summer can be especially tough on trees. Heat waves, drought, and thunderstorms can quickly damage or even kill your trees. To help you keep your trees as healthy as possible throughout the summer (and prevent yellowing and premature leaf drop), check out our Summer Tree Care Tips.

When should I call an arborist?

If your trees don’t look healthy, or if their summer leaves turn yellow and a lot of them drop, have an arborist evaluate them. Your trees are beautiful, valuable investments, and early, professional treatment can keep them healthy for decades to come.

A Final Word

You can prevent many of the causes of premature leaf drop by giving your trees proper care. But even with good care, trees can develop diseases and insect infestations, suffer from unseasonable weather, or be affected by environmental issues. We specialize in caring for Connecticut’s trees and we’re here to help yours. If you feel your trees are struggling or just don’t look their best, give us a call at 203-258-5584 to schedule an appointment with one of our arborists.