Leaves on the trees

Autumn leaves

So what causes the beautiful displays of autumnal colour? The green colour of spring and summer leaves is the result of chlorophyll, the chemical that enables the plant to photosynthesise and produce the energy it needs to grow. Come autumn, the tree starts to break down the chlorophyll and stores the broken-down molecules to have on hand when spring comes, making that first effort of chlorophyll production easier. This means that the green pigment that chlorophyll provides to the leaf is no longer dominant. Other colours—yellow, orange, red, purple—start to show through.

As the tree extracts and breaks down chlorophyll from green leaves, they lose their green colour. Image adapted from: Timothy Eberly; CC0

The red and purple colour are produced by a chemical called anthocyanin. This chemical can also help protect leaves from becoming sun burnt or being eaten by insects. Some trees have anthocyanin in their leaves throughout the year, but many only produce this chemical in the autumn. It reacts with glucose (sugar) held within the leaves to produce the red and purple pigments. Maple leaves are particularly renowned for their beautiful autumn colours—this is because their leaves contain a lot of glucose, which ups the production of anthocyanin.

The yellows and oranges are caused by varying amounts of chemical called carotenoids (also responsible for making carrots orange!). Browns are generally caused by tannins.

Chemicals within the leaves provide the brilliant autumn colours: yellows and oranges are caused by carotenoids; reds and purples by anthocyanin. Image adapted from: Stanley Zimny (Thank You for 28 Million views); CC BY-NC-ND 2.0

The grandeur of autumn colour can vary from year to year depending on weather conditions. More rainfall and increased soil moisture makes for more intense displays of colour. Sunny days also help, as anthocyanin production is helped along by sunlight.

So, the gorgeous displays of colour deciduous trees put on for us aren’t solely to help ease us through that transition from the warm summer nights into the chill frosty mornings of winter—they’re the result of a complex evolutionary strategy to save energy and conserve nutrients, essential to the trees’ growth and survival.

Do Apple Trees Lose Their Leaves in the Winter?

Michael Blann/Digital Vision/Getty Images

Each fall and into winter, apple trees lose their leaves until the following spring. In spring, the tree produces brand new leaves that will stay on the tree through the summer and into the fall.


All apple trees are deciduous, meaning they lose their leaves every year. The leaves usually turn yellow or brown right after the fruit matures and fall completely off the tree by the start of winter. The trees go into a dormant stage during winter, meaning that no new growth occurs during the cold season.


To prevent pests from overwintering on the ground under your apple trees, rake up dead, fallen leaves and properly dispose of them. Removing rotting fruit lying under the tree keeps pests from using the fruit as a place to overwinter.


In mid to late March, apple trees start producing leaf buds as they come out of the dormant stage. The buds turn into new leaves that stay on the tree the rest of the summer and into fall.

Early Leaf Drop of Apple Tree

I have a 15-year-old dwarf golden delicious apple tree. Every year beginning in July it starts dropping it’s leaves. I spray it annually with fungicide and insecticide, but the problem continues. An experienced gardener told me it was the pine trees in my neighbor’s yard causing the problem.

Several fungal diseases can cause apple trees to lose their leaves. Apple scab causes olive green or black spots on the leaves. Leaves eventually drop from the tree. Rust causes orange spots on the leaves. The infested leaves will eventually drop from the tree. The alternate host for this tree is the evergreen red cedar (Juniperus virginiana). This may have been the “pine tree” your experienced gardener was talking about. Removal of all red cedars within a mile of the apple will prevent the disease. This is usually not possible since these plants belong to others. Sanitation will help with both diseases. Rake and destroy leaves as they fall to the ground. Fungicides will also help but timing is critical for success. Fungicides must be applied at bud break and every 10 days for a total of 4 to 5 applications. Additional treatments may be needed during wet weather. Do not spray an insecticide during blossom. They will also kill the important pollinating honeybees. As always read and follow label directions carefully.

Apple Scab Causes Naked Crabapple Trees

Apple scab causes brown lesions on crabapple leaves

By Christine Engelbrecht
Plant Pathology
Iowa State University Extension

Across Iowa, crabapple trees have been dropping leaves this summer. Although many do so every summer, this summer the blatant leaf-dropping has been especially prevalent. What causes these attractive trees to drop their leaves mid-summer? The answer is a fungal disease called apple scab.

A fungus called Venturia inaequalis infects crabapple leaves early in the spring. As the fungus grows in the developing leaves, it causes purplish-brown spots, often clustered along the leaf veins. The spots can grow up to a half inch in diameter, with feathery margins when young and more distinct margins as they mature. Most people don’t notice the disease, though, until these infected leaves turn yellow and fall off the tree. Some people rake the fallen leaves out of their yards daily for weeks, until the tree is almost completely bare by midsummer. The crabapple that was spectacular while blooming in spring has become an eyesore by August.

The apple scab fungus spends the winter in the fallen leaves, and in the spring it produces spores that can infect the new crop of leaves. Besides crabapple, the disease also affects apple, pear, hawthorn and mountain ash. Apple scab is the most economically important disease of commercial apple orchards.

Why do some crabapple trees get hit with scab every year, while others seem to be unharmed most years? Crabapple cultivars vary greatly in their ability to fend off the apple scab fungus. Some popular cultivars, such as “Spring Snow”, are very susceptible to apple scab, and they lose their leaves nearly every year. Other cultivars, such as “Prairifire” are resistant. Even a resistant variety can get apple scab if the weather is very favorable for disease, but in most years it will be disease-free.

We see apple scab every year, but this year the disease has been especially severe in much of Iowa, causing defoliation earlier than usual and causing more severe leaf drop. The severity of many plant diseases is largely dependent on the weather. Apple scab is favored by cool, wet weather in the spring, when the fungus infect the new leaves. Because this spring’s weather was so favorable, some resistant trees that haven’t had apple scab for years are dropping leaves this year.

Although naked trees in summer are ugly, apple scab does not kill crabapples and usually does not seriously hurt them. But we plant crabapples to be pretty, so what can we do to manage apple scab? First, choose a resistant cultivar when planting a new crabapple tree. There are many choices of resistant cultivars with beautiful spring blossoms. Realize that resistance is relative, and a “resistant” cultivar can still become diseased under some conditions—but it will have fewer disease problems than a susceptible cultivar.

Since the apple scab fungus survives the winter in fallen leaves, raking up and destroying those leaves at the end of the season can help to minimize problems next year. Keeping trees well spaced and pruned to promote airflow through the canopy can also help. Sometimes fungicide sprays are used to prevent infection of susceptible cultivars in the spring. However, the sprays must be repeated, and they are ineffective once symptoms appear.

Starting with a resistant cultivar is the best way to ensure that your crabapple stays beautiful and leafy throughout the summer.

Two high resolution photos are available for use with this week’s garden column:
Photo 1: A susceptible crabapple tree has lost most of its leaves to apple scab by midsummer
Photo 2: Apple scab causes brown lesions on crabapple leaves

Maple petiole borer causing leaf drop in maple trees

Why are leaves dropping from my maple trees? A close examination of leaves on the ground will likely show leaves with only a small portion of their stems (petiole). This leaf drop is caused by the feeding of maple petiole borers, Caulocampus acericaulis. Petiole borers are small insects called sawflies, which are non-stinging wasps.

The sawfly is only about 1/6 of an inch long and emerges from the soil in the spring to mate and lay eggs near the base of the petiole of maple leaves. Larvae enter the petiole where they tunnel through the stem of the leaf, feeding for 20 to 30 days. Eventually, the tunneling causes the stems to break and the leaves to fall to the ground in May to June. The larvae do not fall with the leaves, but remain in the portion of the petiole still attached to the tree. After 10 days, the portion of the petiole attached to the tree will fall to the ground with the borer. Larvae leave the petiole and burrow into the soil where they remain until the following spring when they emerge as adult sawflies. There is one generation of maple petiole borer each year.

Damage caused my maple petiole borer. Photo credit: Charles D. Pless, University of Tennessee, Bugwood.org

Though the falling leaves are a nuisance, it will not continue for very long and the proportion of leaves damaged by the borers is usually small and does not harm the plant’s health. Raking leaves up will not help reduce the borers since the larvae are not in leaves that have fallen to the ground. This is one of those moments when the best course of action is no action.

Mulching leaves back into the turf is the best method for disposing of the fallen leaves. Insecticides are not recommended since the problem is not significant to the plant’s health and incidences of this pest are infrequent and unpredictable. Once leaf drop is seen, it would be too late to manage the problem with pesticides.

Though all maples are susceptible to attack from the maple petiole borer, it is common to see leaf drop due to the insect on sugar, red and Norway maples.

Maple Tree Losing Its Leaves Early


An approximately 10 year old maple tree on our bank started to “leaf out” this spring. These young leaves turned brown and now it looks as if the tree has died! I had hoped a drop in temperature early was the cause for the brown leaves, but no green is coming through again.

Also, we have another maple, on the same bank, about 30 feet from the other one. It has loads of maple seeds on it. They’ve never dropped, are still green, but the tree looks okay.

Someone told me sometimes trees will produce an abundance of seeds like that when “it knows it’s going to die.” Yikes! Any clue on that tree and possibly why the other one died while other maples and pin oaks on the same bank are growing fine? We were in a drought, but good rainfall fell just this week.

Hardiness Zone: 7b

Kathy from Canton, NC


I’ve never heard the story about maples making a last ditch effort to reproduce before perishing, but I wouldn’t worry about it. Mature maple trees average a bumper crop of seeds every two or three years. This is especially true of sugar maples. In fact, I have 5 healthy sugar maples in my landscape right now, and only one of them is having a banner seed year. Advertisement

When maples suddenly drop their leaves in June or July, it’s usually due to drought, a sudden change in temperature or insects like scale, aphids or a specific wasp larva that burrows into the leaf petioles.

When the trees are stressed by drought or sucking insects like aphids, the leaves will turn yellow or brown before dropping. These insect infestations are quite unpredictable, and usually only result in a loss of 25% to 30% of the tree’s leaves. Most trees fully recover.

If your entire tree has lost its leaves, it may have sustained some type of serious root damage. This can be the result of drought, over-fertilizing or over-watering in the fall or spring. You can tell if it’s dead by scraping back a bit of the bark. If you see green tissue, the tree is still alive.


I would recommend calling a tree service or a certified arborist to evaluate your tree to make sure your not dealing with a problem that will spread to the other trees. Give your tree until next season. If it fails to leaf out again, it’s probably best to remove it.


Sometimes being arborists is kind of like being a detective. We get calls from property owners both residential and commercial, trying to figure out what is wrong with their tree. Some of these clues lead to easy diagnoses, but others can be puzzling and give us a good amount of work to solve the case.

Maple trees are common throughout our area, and they have been widely used in landscaping both residential and commercial properties. We use Maples a lot in landscape design as well as we often see a multitude of problems with existing Maples. Some of them don’t warrant concern but others do. Some problems can be solved by pruning, or a tree and shrub care program, but others may have no viable solution and may just lead to increasing decline of the tree. In any case, if you are looking at your Maple tree and realizing something just doesn’t look right, these are some of the things to look for:

  • Small leaf size: When leaves start to appear to be getting smaller each year on a plant, it’s a good sign that there is a problem. This could be a result of a disease issue, nutritional deficiency, or the impact of environmental changes or stresses in the past year or so near the tree. Girdling roots can also cause problems as they restrict the vascular flow of water and nutrients up to the leaves.
  • Poor leaf color: If leaves are losing their vibrant, green color during the year, even turning yellow, it could be a sign that your Maple tree isn’t being sufficiently nourished. In some cases, this issue can be corrected by taking a soil test for your tree in the root zone and adding the necessary elements to correct the soil pH and to raise levels of certain materials that are below optimum in the soil. In some cases, certain insect or mite problems can also discolor leaf tissue. These infestations can often be addressed with tree spraying of a labeled material.

  • Spots or growths on leaves: There is a whole host of fungi and phenomenon that can cause strange growths on leaves. Some of these pose minimal health concerns to trees and can even just happen on an isolated year as a cosmetic defect. However, some of these issues may be detrimental to the health of your tree, especially on a chronic basis. Some of these fungi can be reduced by performing preventative disease control spraying or injections. Most of these treatments should occur prior or during leaf emergence, and should be performed each year for protection.
  • Early leaf-drop: Leaves are supposed to drop in fall, not the end of summer. If your tree seems to be changing color or dropping its leaves earlier than it should it is a tell-tale sign that it is under stress. This could be from root issues, drought stress, excessive moisture, or an internal decay problem.
  • Dead limbs or thinning crown: If your Maple tree seems to be losing life to certain branches or it seems to be thinning out each year dropping lots of leaves, it may mean it is in advanced states of decline. This could be from a long history of all sorts of stresses, but can also be the result of girdling roots or other stresses. In some cases, removing girdling roots and addressing other health concerns can slow the decline of the tree, but it most likely will not cause a rapid transformation of the tree. Sloughing bark that breaks off and reveals dead limbs underneath is often a sign that decay has been happening for quite some time in some areas of your tree. These should be evaluated to see if tree pruning or tree removal is recommended.
  • Over-abundance of fruit production: Fruit production on trees is affected by multiple factors, especially weather. Some years the conditions are ideal, causing a big crop of those “whirly-bird” seeds to be falling from your tree. It may even be that they clung to the tree for as long as possible and then were all dislodged at that first windy day. However, stress on a tree can also cause an over-abundance of fruit production in some cases.

Tree decline and death is often the result of multiple factors. Stresses such as drought, excessive moisture, girdling roots, improper pruning, insect and mite damage, and disease can not only make a tree look unsightly, but it can start the progression of decline in a plant’s life. Ignoring or not noticing those issues for years is bad news for a tree. The best way to keep a tree healthy is to address these issues regularly throughout its life, not wait until problems are irreversible. When you plant trees, be sure to use a landscape designer that will make sure your trees are good selections for the site and properly planted.

Start caring for your tree at a young age with both periodic pruning of young trees as well as addressing them with a plant health care program to prevent problems. Using a company that employs numerous Certified Arborists is a good idea as these individuals often spot the early warning signs of these issues and can recommend treatments that may positively impact your Maple tree and others. If your tree is already mature and you’re seeking a diagnosis of a problem, we would be happy to assess your tree and tell you what may be done to handle the issues that are causing it to not look its best.

Why Do Some Trees Keep Their Leaves in Winter?

WHY? is our attempt to answer all the questions every little kid asks. Have a question? Send it to [email protected]

Have you ever wondered why some trees keep their leaves in winter when all the other leaves fall off? Trees have different life cycles, and are either called deciduous (de-SID-you-us) or evergreen. Trees with flat, wide leaves that turn pretty colors in the fall are deciduous. They will drop their leaves when the weather gets cold. Evergreen trees, on the other hand, lose their leaves throughout the year a little bit at a time.

First, we need to talk about how trees get food, or energy. Trees use the energy from sunlight and water to turn carbon dioxide into a kind of food. This process is called photosynthesis (foe-toe-SIN-thuh-SIS). The days get shorter in fall and winter, so there is less sun energy to use. Deciduous trees close up the little holes where the leaves attach so they don’t lose moisture (MOYS-chur), or water. This makes the leaves drop off. Evergreen trees don’t have to drop their leaves.

Evergreen trees first came from cold climates. (But you can find many in warm tropical rainforests too.) They have very strong leaves rolled up tight, like long, thin needles. This shape allows the evergreens to conserve water, which is needed for photosynthesis. Because they have more water than their deciduous cousins, their leaves stay green, and stay attached longer. Evergreen needles also have a very waxy coating that also helps save water during summer and winter. Christmas trees are generally evergreens like spruce, fir, or pine.

To learn more about the lives of trees, watch this short film at National Geographic.

Why Are Trees Losing Leaves in August or Early Fall?

Every autumn, we look forward to seeing tree leaves transform. But what does it mean when trees lose leaves much sooner?

When leaves shed well before the fall season, something might be wrong with your tree’s health. One of our readers in Texas noticed, “Right before fall, my oak tree started losing its leaves way early. Now, it has lost almost all its leaves. What is wrong with my tree?”

Learn why your tree leaves may be falling early.

3 Reasons Why Trees Lose Their Leaves in Early Fall or Summer (June, July or August)

Why are leaves falling off trees already?

There are three general reasons why trees lose their leaves early.

  1. The canopy is crowded. Some trees may have grown more leaves than they can support, so they drop leaves to conserve water in hot, dry weather. th
  2. It’s a pest or disease. See what summer pest could be hurting your tree leaves. If those symptoms don’t match, check if a leaf disease is the issue.
  3. It’s something in the water. Too much or too little water can cause late summer leaf loss. Check your tree’s moisture levels, and then plan the best watering regimen.

Don’t fret if you’re not quite sure which challenge your tree’s dealing with. Here’s how to diagnose leaf drop on your maple, oak or ash tree.

Why is my oak tree losing leaves in summer?

Find out what type of oak tree you have. Live oaks naturally shed leaves in summer, so as long as the leaves are green and healthy, there’s no need to worry!

But if the fallen leaves are discolored or look unhealthy, that could mean a pest or disease. Oak wilt is a common one. First, leaves turn yellow, then brown right before they fall off starting at the top of the tree. These symptoms call for an arborist.

If there are no disease symptoms on your oak, investigate other possible causes, like the tree’s moisture level.

Why is my maple tree losing leaves in summer?

Your maple might be suffering from a petiole borers infestation or tar leaf spot disease.

Did you know the small piece that connects a tree leaf to its stem is called a petiole? Tiny petiole borers feed on that, which makes leaves break from the stem and fall off. Luckily, the amount of leaf loss is small, and the pests don’t pose a real threat to maple trees.

Tar leaf spot is more noticeable. It turns maple leaves yellow, then black before they fall off. You can help manage the disease by raking and disposing of fallen leaves.

Why is my ash tree losing leaves in summer?

Anthracnose, a tree fungus, can cause ash trees to lose their leaves early. Moist, humid weather allows the fungus to thrive and turns leaves a blotchy brown.
Anthracnose tends to not be a huge issue for ash trees. Raking and destroying diseased leaves can help minimize the harm.

And remember, a tree without infestation symptoms may just need water.

Why Do Some Trees Stay Green While Others Lose Their Leaves?

Did you ever wonder why some trees and shrubs stay green all year? Or, conversely, why other trees shed their leaves before winter?

You might think deciduous trees lose their leaves because they’re trying to avoid freezing weather. But they’re actually coping with the drought conditions of winter.

According to Dr. Emile DeVito, New Jersey Conservation Foundation’s staff biologist, the best clue comes from tropical forests with extended dry seasons. When the rainy season ends, soil moisture drops to near zero. Broad leaves typically evaporate lots of water, so even in the warm tropics deciduous trees shed their leaves to prevent tissue death due to drying out.

New Jersey’s deciduous forests do the same thing: becoming leafless during winter for self-protection!

Even during wet winters in New Jersey, water becomes nearly unavailable to tree roots when the soil freezes. Our deciduous oak, maple and birch trees shed their leaves each fall to prepare for drought.

Evergreens, on the other hand, are more efficient at conserving moisture. Evergreen needles are basically rolled leaves, similar to hollow tubes with all their evaporative pores tucked away on the inner wall. “Like penne pasta in a sieve, they resist evaporation by trapping moisture inside,” said Emile.

Hollies and rhododendrons, with tough waxy leaves that resist drying out, don’t need to drop their leaves like maples and dogwoods. Rhododendrons can roll their leaves into tubes to resist freeze-drying in the cold and wind!

Imagine viewing eastern North America from space on an early February day 600 years ago. Back then, evergreen forests of spruce and fir stretched from northern Canada south to the giant hemlock/white pine forests of the Great Lakes and northern New England.

You would see a shift to broadleaf deciduous forests in southern New England and the Highlands of New Jersey, since forests had yet to be cleared for agriculture. Deciduous forests were king from the Atlantic to the Mississippi River, from the south-facing slopes of the Catskills and Berkshires to the low elevations of the Great Smokies. But moving toward coastal New Jersey’s Pine Barrens and the pine and live oak forests of the Deep South, evergreens would re-emerge as the dominant forest types on the landscape, all the way into the tropics.

This winter view of eastern North America in the early 1400s would have been green in the far north and Deep South, with a wide, leafless brown “waistband” from Pittsburgh and Boston south to Little Rock and Chattanooga.

Deep, permanent winter snow cover, though occasional, is not common in this brown, leafless winter waistband!

Without a reliable deep snow cover every winter, soil in the “waistband” region can freeze down to the root zone. For a drought-intolerant species like sugar maple, when the soil freezes it might as well be the Sahara desert.

In the far north, the snow cover is deep and insulating. Snow comes early, before the entire root zone has frozen. Spruce and fir high in the Adirondacks, or white pines and American hemlocks in cold pockets in the New Jersey Highlands, can still make sugar when the sun warms their needles and the temperatures rise into the 40s in mid-winter.

But a short distance to the south, where prolonged snow cover is uncommon, the roots of deciduous oaks, maples and birches can freeze solid. A rhododendron shrub is more likely to have frozen roots and experience “winter burn” at Morven in Princeton than in Tillman’s Ravine Natural Area in northern New Jersey!

Deciduous forests are adaptations to winter drought. Falling leaves are an “evolutionary bet” that deep snow will not be available to protect roots from a deep freeze.

As climate change impacts the predictability of snow cover in northern New Jersey and southern New England, deciduous species could gain an edge over evergreens and expand their range northward. But as the climate fluctuates, alien species are probably more likely to invade the competitive cracks that open up in native species habitats. Natural plant communities are tuned in to long-term climate patterns over the last few thousand years and rapid changes could easily allow aggressive takeovers by alien species and a loss of our forest diversity.

So hold on to your hats when the cold wind blows this winter, and don’t let your toes freeze!

For information on preserving New Jersey’s forests and natural resources, visit the New Jersey Conservation Foundation website at www.njconservation.org or contact me at [email protected]

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