Willow trees die from fungal diseases, wood-boring insects, drought, root rot, salt damage, and natural old age. They can also be killed intentionally with herbicides. Willows are fast-growing but comparatively short-lived trees, with weeping willows typically lasting only 40 to 75 years, so many of the stresses that a longer-lived hardwood could survive will push a willow past the point of recovery.
Willow Blight: The Most Common Killer
The disease most likely to kill a willow is willow blight, which is actually two fungal infections working together. Willow scab attacks the leaves, while black canker attacks the stems and branches. When both are present at the same time, the combined damage can defoliate the tree, kill branches from the tips inward, and eventually kill the entire tree.
The signs are distinctive. Infected leaves shrivel and droop, then develop olive-brown masses of fungal spores on their surface. On the stems, you’ll see dark brown or black sunken patches (cankers), sometimes with peach-colored spore masses. If the disease hits hard in spring during wet weather and repeats over consecutive years, the tree may not recover.
Canker Diseases That Rot From the Inside
Beyond willow blight, canker-forming fungi in the Cytospora group are a serious threat. These pathogens infect the inner bark and cause the sapwood underneath to sink and discolor. In controlled studies, the most aggressive species produced cankers averaging 53 mm in length within just seven days, with 100% of inoculated trees developing visible lesions. The cankers expand, girdling branches or the trunk itself, which cuts off the flow of water and nutrients. Once a canker encircles a branch or the main stem, everything above it dies.
Another fungal killer to watch for is Armillaria root rot. Trees infected with Armillaria show poor growth, dead branches in the upper canopy, and undersized or yellowed leaves. If you peel back the bark near the base, you may find flat white sheets of fungal growth sandwiched between the bark and sapwood. Thick black strands resembling shoestrings sometimes appear under the bark, around the roots, or in the surrounding soil. The internal wood turns white, soft, and spongy, sometimes extending well up into the trunk. Infected willows frequently snap or topple in storms, and clusters of honey-colored mushrooms at the base in fall are a telltale sign.
Root Rot in Waterlogged Soil
Willows love moisture, but constantly saturated soil creates conditions for root rot caused by Phytophthora, a group of water-loving soil pathogens. These organisms produce swimming spores that actively seek out root tissue when free water fills the spaces between soil particles. Once inside, they kill roots and grow upward through the root crown into the lower trunk, destroying the inner bark and browning the outer sapwood.
The frustrating part is that Phytophthora-infected trees look like they need water. Even well-watered willows will wilt because their rotted roots can no longer absorb moisture. Some species of Phytophthora attack in warm, moist soils during summer, while others prefer cool, wet conditions in spring or fall, meaning willows in poorly drained sites face year-round risk.
Borers That Destroy the Wood
The poplar and willow borer is one of the most damaging insect pests of willow trees, and willow is its preferred host. The larvae tunnel through the wood, and when populations build up, they can kill entire stands of trees. Damage includes frass-plugged entrance holes, cracking and weeping bark, sawdust accumulating at the base, and galling of the trunk. The critical damage happens when larval tunnels girdle the tree, cutting off its vascular system the same way a canker would. Weakened wood also invites secondary infections through the borer wounds, compounding the problem.
Drought and Salt Stress
Willows are among the thirstiest trees in any landscape, and drought hits them harder than most species. Research on willow plantations during the extreme 2018 European drought found that carbon uptake dropped significantly under dry conditions and, importantly, showed limited recovery even after the dry period ended. A single severe drought season can cause lasting damage to a willow’s ability to photosynthesize and grow.
Salt is another environmental killer, whether from road de-icing, coastal exposure, or naturally saline soil. Different willow species have very different tolerances, but all of them share the same failure mechanism. Roots can intercept and hold back sodium up to a threshold. Once sodium accumulation in the roots exceeds that limit, the filtering system breaks down and sodium floods into the leaves. At that point, the tree’s ability to selectively absorb nutrients collapses, and death follows quickly. For two commonly studied species, that root threshold was about 34 mg of sodium per gram of root tissue. Some less tolerant species begin withering at much lower salt concentrations.
How to Kill a Willow Tree Intentionally
If you’re trying to remove a willow, four herbicide types are rated excellent for the job: glyphosate, triclopyr, imazapyr, and 2,4-D. All four are systemic, meaning the tree absorbs them and transports them internally to where they do their work. This makes them slower-acting than contact herbicides but far more thorough.
Glyphosate is effective on willows growing above the water line but does not work well on plants actually standing in water. It requires an appropriate surfactant mixed into the solution. Triclopyr is a selective broadleaf herbicide, so it will target the willow without harming nearby grasses. Imazapyr works at low application rates and is effective on willows growing in or near water. 2,4-D is another systemic option, though it is less selective than triclopyr.
For any of these, the most effective approach on a mature willow is a cut-stump application: fell the tree and immediately apply the herbicide to the fresh-cut surface. Willows resprout aggressively from stumps and roots, so simply cutting the tree down without chemical treatment will usually result in a thicket of new growth.
Signs a Willow Is Already Dying
Willow decline often looks gradual until it suddenly isn’t. Early signs include undersized or yellowing leaves, dead branch tips in the upper canopy, and bark that cracks or peels away easily. If you notice soft, spongy wood at the base, white fungal mats under the bark, or black shoestring-like strands in the soil around the roots, the tree likely has advanced root rot and may be structurally unsafe. A willow that leans or whose trunk feels hollow when tapped is a falling hazard, especially in storms.
Because willows grow fast and have relatively soft, weak wood, they deteriorate quickly once decline sets in. A willow that looked fine last year can lose major limbs or topple within a single season if disease, borers, or root rot have been quietly advancing beneath the bark.