Willow trees are beautiful additions to any property and have been regarded as one of the world’s most lovely trees. You probably want to ensure it has a long healthy life as an asset on your property. Discovering yellow leaves may send you into a panic. Don’t worry; we’ve got you covered.
The most common reason a willow tree has yellow leaves is over or underwatering. Willows like moist soil, so drought and extreme heat will cause leaves to wilt and discolor. Prolonged periods of wetness, such as flooding, can also cause yellow leaves.
Willow trees may have yellow leaves for three additional reasons; pests, fungal problems, or environmental issues. Continue reading for more in-depth information on common willow tree problems that can cause yellowing leaves.
How Does Watering Affect Willow Leaf Color?
According to the University of Arizona, mature willow trees should be watered once every ten to twenty days during extreme temperatures or drought. The variability here depends on the type of soil in your area.
Areas with sandy soil and excellent drainage will need to water more often than areas with clay soil and poor drainage.
If you have planted a new willow tree in the last two years, you should water your young tree more often. According to the Univesity of Arizona, newly planted trees should be watered ten gallons for every inch of trunk diameter every three days.
Proper watering includes watering your tree outside the drip line. The drip line is the line around the circumference of the tree’s canopy or where water drips off the tree’s leaves.
Watering outside this circle allows water to flow towards deeper roots. Following this method will prevent you from overwatering the tree.
How To Prevent Your Willow Tree From Having Yellow Leaves
The best way to keep your willow tree happy is to choose a location that will meet its needs. For example, each species of willow tree may prefer slightly different growing conditions.
Generally, willow trees grow best in rich loamy soil in a moist environment. That is why we see so many graceful weeping willows on the banks of rivers, streams, and ponds!
While your willow tree may like moist soil, too much water could become a problem. If the tree’s roots are constantly under water, it never has a chance to dry out and access the oxygen and other elements in the soil.
Your young willow tree will do the best in full sun, but it is essential to water it consistently throughout its first two years on your property.
Under these conditions, a willow tree will grow in almost any environment. However, there is one more important consideration when finding the perfect location for your new willow tree.
Willow trees have long drooping branches that can be susceptible to storms and strong winds. If possible, a location in the dip of a valley or other wind-protected site will make it even happier.
Caring For A Willow Tree With Yellow Leaves
If you have noticed yellow leaves on your tree, and you made sure you are properly watering your tree, it’s time to look at some of the other reasons your tree’s leaves may be yellowing.
Willow tree leaves are yellow for three main reasons besides watering; pests, fungal problems, and environmental issues. Let’s review each of these three in more detail and find solutions.
According to the University of California’s Department of Agriculture and Natural Resources, three common problems can occur a willow three and turn its leaves yellow, pests, fungus, and environmental issues.
Additionally, when you are first planting your tree, you want to make sure that you are planting a willow tree where it will actually want to grow. Planting them in good spots can ensure that its leaves will stay green and healthy!
Common Willow Tree Pests That can Cause Yellow Leaves
The following is a list of willow tree pests. We will go into greater detail into each further into the article.
- Aphids
- Armored scales
- Carpenterworm
- Boring insects
- Foliage-eating caterpillars
- Leaf eating beetles
Aphids
Aphids are small insects with long strawlike mouths that they use to pierce the tender parts of the plant and suck out the fluids.
Aphids are widespread plant pests, and most plants can become susceptible. For example, large colonies of aphids can turn the leaves of your willow tree yellow.
There are many types of aphids, but three kinds are known to prey upon willow trees:
- Giant bark aphid
- Giant willow aphid
- Melon aphid
Aphids alone are not a big enough pest to significantly harm a mature willow tree. However, if you have a big aphid problem, consider controlling them without pesticides by introducing lady beetles to your tree.
Also, consider applying Pre-Fed Live Ladybugs to your willow to help with aphid population control.
Armored Scales
Similar to aphids, scales are sucking insects that suck the juices out of the bark or leaves of a willow tree. They are unique-looking bugs that can be easily missed.
Some species can seriously damage their host plant turning the leaves yellow and causing them to drop before the fall season.
There are many kinds of armored scales, but three have been known to feed on a willow tree:
- Greedy scale
- Latania scale
- Oystershell scale
- San Jose scale
An early application of Monterey Horticultural Oil applied early in the spring can reduce the prevalence of armored scales.
Carpenterworm
Carpenterworms in the larva stage are large caterpillars that bore into willow wood and feed on their inner bark. Willow trees along river banks are the most susceptible to the carpenter worm.
The best management of carpenter worms is prevention. Take good care of your tree and limit injury to its bark.
Wounds on the bark of the willow tree can become significant targets for this woodboring worm. Unfortunately, conventional insecticides are ineffective against pests underneath the bark.
Nematodes are an excellent option for controlling carpenter worms. Check out NaturesGoodGuys Live Beneficial Nematodes and follow the instructions for application.
Borers
Several different species of insects can dig tunnels into the trunk of a tree, called boring, and wreak havoc.
Some of these can prey on a willow tree. Dying limbs, gnarled bark, and swelling around branches and twigs are reasonable indications of a boring insect.
These insects burrow into the tree and leave behind a tiny tunnel that may exude destroyed plant matter. These insects can kill entire branches of trees, turning the leaves yellow before they fall to the ground.
Mature trees can usually recover quickly from a few boring insects, but if you have a bigger problem, you may want to apply nematodes.
Insecticides such as Bio Advanced Tree and Shrub Protect and Feed applied in the spring when the insects are in their reproductive cycle can work if you get the timing right.
Foliage-Feeding Caterpillars
Caterpillars are butterflies and moths in their larval stage. They often eat the leaves of trees and shrubs such as the willow. This type of damage can turn leaves yellow.
Foliage-feeding caterpillars that could prey upon your willow tree include:
- One-eyed Sphinx
- Fruit tree leafroller
- Omnivorous looper
- Redhumped caterpillar
- Tent caterpillars
- Western Tiger Swallowtail
These larvae feed on the young leaves of the willow tree and may chew down to the mid-rib of each leaf. This pest is the hardest on young plants, while mature trees fare better.
Manage foliage-feeding caterpillars by cutting off infested leaves. Then, scrape the caterpillars and their nests and eggs into a bucket of soapy water or burn the removed foliage. Again, prevention is the best tool for keeping your tree well-pruned.
Leaf-Eating Beatles
According to Cornell’s School of Integrative Plant Sciences, Leaf feeding insects such as the Japanese beetle can chew the leaves right off the plant. In addition to the Japanese beetle, other kinds of beetles also eat willow trees.
Additional types of leaf-eating beetles include:
- Willow beetle
- Cottonwood leaf beetle
This type of bug damage causes the leaf to curl at the edges and may slow the tree’s growth.
Harmful Willow Tree Fungi That Cause Yellowing
The following is a list of funguses that affect willow trees in the United States and may cause yellowing leaves:
- Powdery mildew
- Rusts
- Scab
- Crown Gall
- Black Canker
Certain plants can even attract pests to attack your willow tree, which may cause them to have yellow leaves. Check out our article to learn more about the plants that you should not grow with a willow tree.
Powdery Mildew
This willow fungus can be recognized by a white powdery substance on the leaf’s surface. It can be particularly hard on young woody trees and shrubs like the willow. New growth may appear stunted, shriveled, and discolored. Infected leaves turn yellow and die off before healthy leaves.
To handle powdery mildew, situate your tree in a sunny area with good air circulation. Consider applying a natural fungicide such as Natiria Neem Oil Spray.
Rust
Rust looks like small orange pustules on the leaf’s surface. This fungal problem needs an alternate host to reproduce but can infect and reinfect your willow all summer long and may overwinter on the dead leaves, ready to reinfect your tree next spring.
Rust usually occurs on a willow tree’s young twigs and green leaves. Rust infects plants when they are wet, and temperatures are cool.
Prevent rust by watering outside the dripline and only watering the recommended amount.
Avoid overwatering your willow tree to avoid rust. Instead, collect infected leaves as they fall on the ground and discard them far away from any other plant.
Scab
Willow Scab, an additional fungal enemy of the willow, appears as small green-brown-yellow masses on leaves and twigs of the willow tree. It can cause the leaves to turn yellow, wither, and drop to the ground prematurely.
Scab infections in a single year do not pose a significant threat to a willow tree; however, conditions that occur year after year can reduce the tree’s overall growth. Limited growth may appear as twigs and branches dying off.
This problem may not be the cause of a dying tree, but it does make it more susceptible to the other issues and pests on this list.
In most cases, Scab can be tolerated by a mature willow tree. Remove fallen leaves and debris quickly. Most fungus thrives in moisture, so water your tree early in the day so that it has time to dry out in the sun.
Crown Gall
According to Pennsylvania State Extension, Crown Gall forms rough bulging growths, called galls on stems, roots, or at the soil line. Bacteria cause this problem.
The best control tactic is to remove severely affected trees and replace the trees with trees that are not susceptible to crown gall.
Black Canker
Have you ever seen an unusual growth on a willow tree and wondered what it was? Black Canker is a problem that can occur in a willow tree.
It forms black areas on leaves and may spread to kill larger twigs and branches in the summer, yellowing the leaves as the branch dies. If the weather is particularly wet, pink masses form on the blackened twigs.
Black canker often occurs on trees with blight. Manage this disease by avoiding planting susceptible trees in this area or applying a fungicide.
Environmental Concerns That Can Cause Willow Yellowing
The following is a list of environmental problems that could turn your willow tree’s leaves yellow:
- Frost
- Nutrient deficiencies
- Poor watering
- Sunburn
- Small Mammals
- Weeds
Frost
Freezing temperatures can damage the leaves, bark, and buds. This damage is most common during the coldest times of spring and fall, especially if the temperature quickly declines after a warm spell.
Unfortunately, you may not notice your willow has been injured until days have passed and the edges of the leaves have gone yellow.
Choose a willow tree that thrives in your climate to prevent frost damage from hurting your tree and causing yellow leaves.
Soak the top three inches of soil with water when unseasonably cold weather is expected.
Soaking will help the soil retain heat, protecting the tree’s roots.
Nutrient Deficiencies
For healthy growth, willow trees need to absorb certain mineral nutrients from the soil. A nutrient deficiency may result in discolored and faded foliage.
If your willow tree is planted in landscaped soil, it probably has all the nutrients it needs. However, if your soil is sandy, the tree may need fertilizers to ensure it has all it needs to grow healthy and strong.
If you suspect your willow may suffer from a nutrient deficiency, consider testing your soil with the Luster Leaf Rapitest Soil Test Kit. This kit tests for PH level, Nitrogen, Phosphorus, and Potash, all critical soil nutrients.
Poor Watering
As we have already discussed, too much or too little water is the most common cause of yellow leaves on a willow tree.
Signs of a poor watering schedule can include wilting land and discolored leaves. Because it is so common, ensure your tree is appropriately watered before investigating any other causes in this article.
If you live in an area susceptible to drought, water your willow tree at least during the drought season. If you have clay soil with little drainage, be extra careful not to overwater your willow tree.
Sunburn
Sunburn is common in newly planted young trees. It can damage the bark, leaves, and any other part of the tree above the ground. Sunburnt leaves will yellow and fall to the ground.
Often the damage is from too much sun during unseasonably warm weather. Sunburn can get worse if the tree needs to be watered. In addition, a sunburned tree is more susceptible to pests.
While the tree is still young, keep the lower branches intact to shade the soil around the plant’s root ball. Shade around the base of the tree will keep the ground there moist and cool and reduce sunburn.
Avoid sunburn by planting your willow tree with enough room to grow as they get larger. In addition, you can prevent sunburn in young tees by whitewashing their trunks with a diluted interior white paint!
Small Mammals
Mice, chipmunks, and rabbits all have a habit of chewing on the tasty young bark of a willow tree. If one of these animals chews its way around the base of the tree, it is called girdling. Fortunately, mature trees have bark that is too tough for these animals.
A young tree that has been girdled will have wilting and yellowed leaves. Look at the base of your tree. If you see a ring of missing bark, your tree has been girdled.
Use Dimex EasyFlex Plastic Tree Trunk Protectors To protect your young willow trees from girdling by small mammals.
Weeds
Weeds near the base of a willow tree will suck the nutrients out of the soil and make the tree compete for precious water. In addition, weeds could result in yellowing leaves that fall to the ground prematurely.
A mature willow tree will not be bothered by the weeks at the base of its trunk, but if you have a newly planted young willow tree, you will want to keep weeds and other plants away from the bottom of the tree. Place two to three inches of mulch around the tree to prevent weeds.
If mulch isn’t your thing, consider using ECOgardener Premium Five Ounce Pro Garden Weed Barrier and Landscape Fabric instead. Make sure to leave plenty of room around the base of your tree to account for yearly growth.
Lets Review!
Willow trees add drama and whimsy to any property, but no one wants to see their favorite tree’s leaves turning yellow and falling to the ground prematurely.
If your willow tree’s leaves turn yellow, the most likely reason is over or underwatering. Young trees should be watered ten gallons for every inch of trunk diameter every three days.
Avoid overwatering your tree by applying the water outside the drip line. Mature willow trees only need watering during times of extreme heat or drought.
If watering is not the problem for your yellowing willow leaves, it may be another common pest, fungal or environmental problem.
Come back to this article to review these after you have ruled out a watering problem. If the problem persists, don’t hesitate to reach out to your local arborist!
Most willow trees will never need the kinds of intervention described here, but with the right tips and tools, you will be ready to tackle any willow tree problem that comes your way.
References
Charles, J. G., Nef, L., Allegro, G., Collins, C. M., Delplanque, A., Gimenez, R., … & Augustin, S. (2014). Insects and other pests of poplars and willows. Poplars and willows: trees for society and the environment. CABI, Oxford, 459-526.
De Vos, B., Huvenne, H., Messens, E., & Maes, M. (2007). The nutritional imbalance caused by nitrogen excess is correlated with the occurrence of watermark disease in white willow. Plant and Soil, 301(1), 215-232.
Isebrands, J. G., & Richardson, J. (Eds.). (2014). Poplars and willows: trees for society and the environment. CABI.
