Willows grow so fast and look so tough that it can be a shock when one starts to fail. The truth is that willows live fast and often die young. The University of Florida notes that weeping willows are usually short-lived, to about 30 years, even with good care. Many willows that “suddenly” decline are really reacting to stress that built up over several seasons. The trick is working out which kind of stress you are dealing with, because some causes are easy to fix and others are not.
The short answer: the most common reasons a willow declines are drought or a sudden change in water, the fungal diseases willow scab and black canker (together called willow blight), trunk and branch cankers, wood-boring insects, root damage, and simple old age. Thin, yellowing leaves and leaf drop in a dry spell point to water stress. Blackened young leaves and dead shoot tips in spring point to willow blight. Dead branches with sunken bark, or holes and sawdust in the trunk, point to cankers or borers, and those need an arborist’s look.
First, check whether it is really dying
Willows drop leaves readily. The University of Florida notes that weeping willow loses some leaves during drought without irrigation, and some yellow leaves in late summer are normal. Before you worry, look at the twigs. Bend a thin twig: living wood is flexible, and if you scratch the bark with a thumbnail you will see green underneath. Brittle twigs with brown, dry tissue are dead. If most of the crown has live, flexible twigs and plump buds, the tree is stressed rather than dying. See why weeping willows lose leaves for the seasonal causes.
1. Water stress
Willows are built for wet ground. UC IPM notes they do best in full sun with ample water. When a willow planted beside a lawn faces a dry summer, it may thin, yellow and drop leaves. Severe or repeated drought weakens the tree and opens the door to cankers and borers.
What to do:
- Water deeply at and beyond the drip line during dry spells, rather than giving frequent light sprinkles. The Morton Arboretum recommends watering so moisture reaches at least 5 to 6 inches down, and checking the soil with a trowel first.
- Mulch a wide ring under the canopy, keeping mulch off the trunk.
- Too much water is rarely the problem for a willow, but a sudden change, such as a drained pond or a new drainage system, can cause decline.
2. Willow scab and black canker (willow blight)
These two fungal diseases are the classic cause of a willow that looks scorched in spring. The University of Illinois explains that willow scab infects leaves as they expand in early spring, spreads through the leaf stalk into young twigs and forms dark cankers that girdle them. Olive-brown spore masses form on leaf undersides. Black canker shows up later, from late spring into summer, with irregular brown to black leaf lesions and small sunken cankers on twigs. When both are present the tree has “willow blight,” which can cause heavy leaf loss and dieback.
Montana State University recommends pruning out and disposing of infected branches, disinfecting tools between cuts, improving air circulation and avoiding long periods of wet leaves. Fungicides are usually not recommended for landscape trees. The University of Florida notes weeping willow appears to be resistant to black canker. Read more in how to treat willow tree fungus.
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3. Cankers on the trunk and large branches
The University of Florida notes that many fungi cause cankers on willow, and if a canker girdles the trunk, the tree will die. Cankers often look like sunken, discolored or cracked patches of bark, sometimes oozing. Infected branches should be pruned out. Stressed trees are much more likely to be infected, so watering and avoiding wounds are the best prevention.
4. Borers and other insects
UC IPM lists several wood borers on willow, including flatheaded borers, poplar and willow borer, clearwing moths, longhorned beetles and carpenterworm. Signs include holes in the bark, sawdust-like frass at the base or in bark cracks, and dieback above the damage. Borers usually attack trees that are already weakened. Leaf-feeding insects such as aphids, leaf beetles and caterpillars rarely kill a healthy willow on their own; see what is eating my willow tree.
5. Root problems
The University of Florida notes that root rot can occasionally infect willow roots and cause decline. Roots can also be damaged by trenching, grade changes, soil compaction from vehicles, or paving over the root zone. Damage underground often shows up as a slow thinning of the crown, starting at the top.
6. Old age and storm damage
Willows have brittle wood. The University of Florida notes they are susceptible to breakage at weak branch unions and that the wood itself tends to break. A willow that has lost big limbs in storms often develops decay at the wounds. Combined with a short natural lifespan, this means a 30- or 40-year-old willow in decline may simply be reaching the end of its life.
Quick symptom guide
| What you see | Likely cause | First step |
|---|---|---|
| Thin, yellow leaves and leaf drop in a dry summer | Water stress | Deep watering and mulch |
| Black young leaves and dead shoot tips in spring | Willow scab or black canker | Prune out infected twigs |
| Sunken, cracked bark on a branch or trunk | Canker | Prune branch; arborist for trunk |
| Holes, sawdust, dieback above | Borers | Arborist assessment |
| Slow thinning from the top down | Root damage or decline | Check for construction or compaction |
| Large dead limbs, decay at old wounds | Age and decay | Arborist risk check |
When to call an arborist
Call a certified arborist if more than a third of the crown is dead, if there are cankers or cracks on the main trunk, if you see mushrooms or conks at the base, or if a big willow is near your house, a driveway or a play area. Willow wood fails easily, and a declining tree can drop limbs without warning. For siting a replacement, see how far a willow should be from a house and when to plant willow trees.
Sources
- Salix babylonica: Weeping Willow (ENH-734), University of Florida IFAS Extension
- Willow, UC Statewide IPM Program
- Scab and Black Canker of Willow, University of Illinois Home, Yard and Garden Newsletter
- Black Canker of Willow, Montana State University Extension
- Watering Trees and Shrubs, The Morton Arboretum
Top photo: Wilfred Helmlinger, CC BY-SA 4.0, via Wikimedia Commons