Weeping willows drop leaves more readily than most trees. Some of that is normal, and some is a sign of stress or disease. The timing, and what the leaves look like before they fall, usually tell you which.

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The short answer: the most common cause of a weeping willow losing leaves in summer is drought. The University of Florida notes weeping willows survive dry spells but lose leaves without irrigation. Yellowing and some leaf drop in late summer is also normal. Blackened young leaves in spring point to willow scab; yellow spots underneath point to rust; chewed, skeletonized leaves suggest willow leaf beetles or caterpillars.

What is causing the leaf drop?

When and what	Likely cause	How serious
Summer, yellow leaves dropping, dry weather	Drought stress	Moderate, fixable with water
Late summer to fall, steady yellowing	Normal seasonal shedding	Not a problem
Spring, young leaves turn black and shrivel, shoots die back	Willow scab or willow blight	Moderate to serious
Yellow spots on the undersides of leaves, early drop	Rust	Moderate
Brown or black spots, mostly cosmetic	Leaf spots or tar spot	Minor
Leaves chewed or skeletonized	Willow leaf beetle, caterpillars	Usually minor
Branches dying, sunken patches on bark	Canker diseases	Serious if on trunk

Drought: the number one cause

Willows are trees of wet places. In a typical yard, they can run short of water quickly in summer. UF IFAS says weeping willow will survive drought but loses some leaves without irrigation, and recommends regular watering in drier, more open sites to prevent leaf drop.

The Morton Arboretum advises checking the soil rather than watering on a schedule: if the top inch or two of soil is dry, water deeply so moisture reaches 5 to 6 inches down. About an inch of water applied at once usually does it. Mulch over the root zone helps keep the soil moist.

Normal leaf drop

Weeping willows shed some leaves through the season, and UF IFAS notes that their thin leaves turn yellow before falling in autumn. A light fall of yellow leaves in late summer on a tree that otherwise looks full is not a concern. Willows also drop a lot of twigs, which UF IFAS lists as a source of significant litter.

Willow scab and willow blight

UF IFAS describes willow scab as a fungus that attacks and kills young leaves within a very short time, then enters twigs, kills back young shoots and causes cankers. Look for olive-green spore masses along the veins on the undersides of leaves. When scab combines with a second fungus, the result is willow blight.

What to do: prune out infected branches in dry weather, rake up fallen leaves and, for new plantings, choose resistant species.

Rust

Rust causes yellow spots on the lower surfaces of willow leaves and, in severe cases, defoliation, according to UF IFAS. Rake up and destroy fallen leaves from affected trees to reduce next year’s infection.

Leaf spots and tar spot

Many fungi cause leaf spots on willows. UF IFAS notes they are rarely serious enough to justify sprays, and that tar spot, which causes black, raised spots, is harmless. Raking up fallen leaves in fall is the main control.

Insects

The Morton Arboretum lists willow leaf beetles and scale insects among white willow’s common pests, and UF IFAS mentions scales, caterpillars, borers and aphids on weeping willow. Leaf beetles and caterpillars chew leaves; heavy feeding can cause early drop. Healthy willows usually leaf out again. Aphids leave sticky honeydew but rarely cause major leaf loss on their own.

Cankers

Many fungi cause cankers on willow branches: sunken, discolored patches on the bark, often with dying leaves above. UF IFAS recommends pruning out infected branches and warns that if the trunk is infected and girdled, the tree will die. Cankers often follow drought or other stress.

Root problems

Construction, soil compaction, trenching for utilities or a sudden change in the water table can damage roots and cause a willow to thin and drop leaves over a season or two. UF IFAS also notes that root rot can occasionally infect willows and cause decline.

What you can do now

Check the soil moisture and water deeply if it is dry.
Spread mulch over the root zone, kept away from the trunk.
Rake up and remove fallen leaves if you see spots, scab or rust.
Prune out dead and cankered branches during dry weather.
Avoid heavy fertilizing of a stressed tree.

When to call a certified arborist

If more than a third of the crown is bare in midsummer, if large branches are dying or if you see cankers on the trunk, ask a certified arborist to assess the tree. Willows are brittle, and a declining tree near a house can be a hazard. Remember that weeping willows are usually short-lived, often around 30 years according to UF IFAS. The ISA Find an Arborist directory lists certified professionals.

For prevention, see when to prune a willow and when to plant willow trees.

Sources

Salix babylonica: Weeping Willow (ENH-734), University of Florida IFAS Extension
White Willow, The Morton Arboretum
Willow, UC Statewide IPM Program
Watering Trees and Shrubs, The Morton Arboretum

Top photo: Ryan Hodnett, CC BY-SA 4.0, via Wikimedia Commons

Why Is My Weeping Willow Losing Leaves?