Willows are one of the most popular trees in the insect world. Their soft, fast-growing leaves feed beetles, sawflies, caterpillars and aphids all summer. The good news is that most of this feeding looks worse than it is. A healthy willow can lose a lot of leaves and still push out new ones. The key is identifying the culprit, so you know whether to wait it out, spray a small tree, or call an arborist about something in the wood.
The short answer: the most common willow leaf-eaters are the imported willow leaf beetle (small, shiny blue-black beetles that chew holes, with dark larvae that skeletonize leaves), willow sawflies (black, yellow-spotted larvae that eat whole leaves in groups), and caterpillars such as the mourning cloak. Aphids suck sap and leave sticky honeydew and black sooty mold. Holes and sawdust in the trunk point to wood borers, which are more serious. Most leaf feeding does not kill a healthy willow.
Imported willow leaf beetle
This is the pest people notice most often.
- Adults: the University of Minnesota describes them as bluish-black to greenish blue and about 1/8 to 1/4 inch long. NC State notes they resemble a black lady beetle.
- Larvae: dark, almost black, about 1/4 inch long. They feed on the leaf surface between the veins, leaving a see-through “windowpane” or skeletonized look.
- Eggs: clusters of yellow eggs on the undersides of leaves, starting in May.
- Damage: adults chew holes and notches in leaves. Virginia Cooperative Extension notes infested leaves become marked with frass, look brown and ragged, and may drop early.
NC State notes there are at least two generations a year, and Virginia Tech says two or three. Minnesota notes the beetle prefers willows and poplars, especially weeping willow.
Does it need treatment?
Usually not on large, established trees. Virginia Tech notes most trees can withstand total defoliation by this beetle as long as it does not happen every year, especially if the weather lets them leaf out again before fall. Treatment may be justified for heavy infestations on small or newly planted trees.
Virginia Tech recommends monitoring in May and June and treating when the yellow eggs first appear, directing the spray to the undersides of leaves. Encourage natural predators such as lady beetles and assassin bugs, which feed on the eggs and larvae.
Willow sawfly
Sawfly larvae look like caterpillars but are relatives of wasps. The University of Minnesota describes willow sawfly larvae as greenish black to black with a black head and large yellow spots on the sides, growing to about 3/4 inch long. They feed in groups, starting at leaf edges and eating whole leaves as they grow.
The University of Kentucky notes the first generation is active in May and a second in July, with pupae spending the winter in the soil under the tree. On small trees you can often prune off or pick off clusters of larvae.
Caterpillars
Several caterpillars feed on willow. The University of Kentucky describes the mourning cloak butterfly caterpillar as black with many fine white specks, larger red-brown spots on its back and a double row of black spines. Small groups feed together on foliage. The University of Florida notes that willow is a favored host of the gypsy moth, now called spongy moth.
UC IPM also lists foliage-feeding caterpillars, leafrollers and the redhumped caterpillar among willow pests. Most caterpillar outbreaks are short and do not seriously harm established trees.
Cottonwood leaf beetle
The University of Kentucky notes that both larvae and adults of the cottonwood leaf beetle feed on willows. Adults are yellow-orange with black stripes and spots. Larvae skeletonize leaves, and adults feed along the veins and midrib. There are several generations a year.
Recommended Products
These are ready to plant and should be put in the ground according to the included instructions upon arrival. All pictures are of fully grown plants. Sizes shipped are in the title and description. Deciduous plants do not have leaves in the winter.
Three Distinct Willow Varieties: Grow a diverse collection featuring Weeping Willow, Austree Hybrid Willow, and Corkscrew Willow trees. Each variety offers different ornamental characteristics, from elegant cascading branches to upright leafy growth and unusual twisted stems that add visual interest to outdoor landscapes.
Unique Twisting Branches And Curled Leaves: Green Curly Willow develops naturally contorted branches, spiraling young stems, and narrow green leaves that may curl or twist. Its sculptural growth creates a distinctive ornamental appearance, particularly during winter when the exposed twisting branches become the main attraction.
Aphids
Aphids are soft-bodied, sap-sucking insects that cluster on the undersides of tender new growth. The University of Kentucky explains that heavy infestations can make leaves wilt or yellow and drop early, but aphid feeding generally does not seriously harm healthy, established trees. Their sugary waste, honeydew, drips onto cars and patios and grows black sooty mold. Kentucky notes the honeydew can also attract ants, flies and wasps.
On a healthy willow, aphids usually need no treatment. Natural enemies such as lady beetles feed on them, and broad-spectrum sprays can kill those helpers too.
Recommended Products
_-_Mississauga,_Ontario_01.jpg){kind=link}
DAILY CLEANSING BAR – Handmade solid soap designed for everyday external cleansing during bathing and showering.
Wood borers: the serious ones
If the damage is in the wood rather than the leaves, take it seriously. UC IPM lists flatheaded borers, poplar and willow borer, clearwing moths, longhorned beetles and carpenterworm on willow. Signs include round or oval holes in the bark, sawdust-like frass in bark cracks or at the base, oozing, and branches dying back above the damage. Borers mostly attack trees already weakened by drought, disease or injury. A certified arborist can confirm the borer and decide whether the tree can be saved.
Identification guide
| What you see | Likely pest |
|---|---|
| Small holes and notches, shiny blue-black beetles | Imported willow leaf beetle adults |
| See-through, skeletonized leaves, dark larvae | Imported willow leaf beetle larvae |
| Whole leaves eaten by groups of black, yellow-spotted larvae | Willow sawfly |
| Spiny black caterpillars in groups | Mourning cloak caterpillars |
| Sticky leaves, black coating, ants | Aphids |
| Holes and sawdust in trunk, branch dieback | Wood borers |
Keep the tree strong
Most willow pests take advantage of stressed trees. Water deeply during dry spells, avoid wounding the trunk with mowers, and prune at the right time; see when to prune a willow tree. If your willow is thinning badly even after the insects are gone, read why is my willow tree dying and how to treat willow tree fungus.
Sources
- Imported Willow Leaf Beetle, NC State Extension
- Imported Willow Leaf Beetle (ENTO-139), Virginia Cooperative Extension
- Willow: Holes in Leaves, University of Minnesota Extension
- Common Insect Pests of Willow, University of Kentucky Entomology
- Willow, UC Statewide IPM Program
- Salix babylonica: Weeping Willow (ENH-734), University of Florida IFAS Extension
Top photo: Ryan Hodnett, CC BY-SA 4.0, via Wikimedia Commons