Fall webworm

Hyphantria cunea

156 host plants

Last updated

Fall webworm creates distinctive web tents on branch tips of alders, cherries, apples, and many other deciduous trees in late August and September. You will see white, silken webs with green, gregarious caterpillars inside feeding on enclosed foliage. Though the tents are unsightly, damage is usually minor and defoliation occurs so late in the season that tree health is rarely compromised. Small trees can be completely defoliated, but established trees typically lose only scattered branch tips.

Remove webs by hand or prune out webbed branches and destroy them to eliminate caterpillars. No other management is necessary for most trees. Bacillus thuringiensis (Bt) can be applied into tents if populations are high on valuable small trees, but application inside the web is difficult. Most trees tolerate fall defoliation without harm since the growing season is nearly finished. Allow natural parasitoids to suppress populations naturally.

Quick Reference

Order
Lepidoptera
Type
defoliator
Host Plants
156
GDD₃₂ Egg hatch/early instar 2nd gen
5,825
Indicator: Crape myrtle Natchez first bloom
Peak Activity
May-June: Adult moth emergence and egg-laying. June-September: Larval feeding...
Damage Severity
cosmetic
Now: Adult Emergence & Egg-LayingLow Risk

White moths emerge in late spring to early summer at approximately 829 GDD50. Adults lay egg masses (several hundred eggs) on the undersides of leaves, covered with body hairs. Eggs hatch in about one week.

Next: Larval Feeding & Web Building

Fall webworm Egg hatch/early instar 2nd gen typically begins around 5825 GDD₃₂. As of June 3, 2026, Puget Sound stations range from 2435.5 to 2672.8 GDD₃₂, approximately 3152 units before the expected threshold.

Regional Season Tracker

GDD₃₂ accumulation across 7 Puget Sound stations · as of Jun 3, 2026
Station GDD₃₂ Current Stage Next To Go
Issaquah / East King 2,673 Pre-season Egg hatch/early instar 2nd gen 3,152
Kent / Auburn 2,665 Pre-season Egg hatch/early instar 2nd gen 3,160
Seattle / UW 2,610 Pre-season Egg hatch/early instar 2nd gen 3,215
Olympia / Tumwater 2,570 Pre-season Egg hatch/early instar 2nd gen 3,256
Tacoma / Puyallup 2,535 Pre-season Egg hatch/early instar 2nd gen 3,290
Bellingham / Whatcom 2,533 Pre-season Egg hatch/early instar 2nd gen 3,292
Sequim / Rain Shadow 2,436 Pre-season Egg hatch/early instar 2nd gen 3,390
Regional estimate

Source: UMD IPMnet catalog (829 GDD50 for adult emergence/egg laying). Wisconsin Extension: second generation in southern areas 791-1540 GDD. PNW has single generation only. About GDD₃₂ →

Monitoring & Action

How to Monitor

Watch for white silk tents at branch tips of deciduous trees beginning in mid-summer. Tents are most conspicuous in August and September when they have been enlarged by maturing larvae. Tents are easiest to spot from a distance when backlit by afternoon sun. Early detection allows removal before tents become large.

When to Act

Treatment is rarely necessary. Damage is cosmetic and occurs late in the growing season when trees have already stored reserves. Intervention justified only for aesthetic reasons on specimen trees or when webbing is extensive on small or newly planted trees.

What Damage Looks Like

Larvae spin conspicuous communal silk tents (webs) at branch tips, progressively enlarging them as they feed. Tents are loose, messy, and can eventually enclose entire branch ends. Larvae feed inside the tent, skeletonizing leaves (young larvae eat upper surface only; older larvae consume entire leaves except major veins). Heavily infested branches are completely defoliated within the web. Damage occurs in late summer and fall (August-September peak), by which time trees have already completed most of their seasonal growth. Damage is cosmetic: fall webworm does not harm otherwise healthy trees. Even complete defoliation of affected branches does not threaten tree survival because carbohydrate reserves are already stored.

Cultural Controls

  • Prune out and destroy tents while they are small (before larvae mature and disperse). Most effective early in the season when tents are concentrated on branch tips.
  • On small trees, physically remove tents by hand or with a pole. Drop into soapy water to kill larvae.
  • Accept cosmetic damage on large, healthy trees. Fall webworm does not threaten tree survival. Defoliation in late summer has minimal impact on tree health.
  • Maintain overall tree health with proper watering and mulching to improve tolerance.
  • Do NOT burn tents in trees. This is a common folk practice that damages bark and cambium far more than the webworms themselves.

Host Plants (156)

Acer crataegifolium Hawthorn, Maple Alnus alnobetula Circumpolar alder group Alnus alnobetula subsp. crispa American Green Alder, Mountain Alder, Green Alder Alnus alnobetula subsp. sinuata Sitka Alder, Wavy Leaf Alder Alnus cordata Italian Alder Alnus glutinosa Common Alder, European Alder, Black Alder Alnus incana subsp. rugosa Speckled Alder Alnus incana subsp. tenuifolia Thinleaf Alder, Mountain Alder Alnus japonica Japanese Alder Alnus rhombifolia White Alder Alnus rubra Red Alder Alnus rubra f. pinnatisecta Cutleaf Red Alder Alnus sinuata Sitka Alder Betula alleghaniensis Yellow Birch Betula davurica Asian Black Birch, Dahurian Birch Betula glandulosa Dwarf Birch Bog Birch, Scrub Birch Betula lenta Sweet Birch, Cherry Birch, Black Birch Betula maximowicziana Monarch Birch Betula nana Dwarf Birch, Bog Birch Betula nigra River Birch, Black Birch Betula occidentalis Water Birch, Western Birch, Red Birch, River Birch, Black Birch Betula papyrifera Paper Birch Betula pendula European White Birch Betula platyphylla Asian White Birch, Manchurian Birch Betula populifolia Gray Birch, Fire Birch Betula pubescens Downy Birch, Moor Birch Betula utilis Himalayan Birch, Bhojpatra, Indian Paper Birch Betula utilis subsp. albosinensis Chinese Paper Birch, Chinese Red Birch Betula utilis subsp. jacquemontii Whitebarked Himalayan Birch Crataegus Hawthorn Crataegus ambigua Russian Hawthorn Crataegus autumn Crataegus autumn Crataegus columbiana Columbia Hawthorn Crataegus crus Crataegus crus Crataegus douglasii Black Hawthorn Crataegus germanica Medlar Crataegus laevigata Midland Hawthorn, English Hawthorn Crataegus lavallei Lavalle Hawthorn, Carrierei Hawthorn Crataegus monogyna Singleseed Hawthorn, Common Hawthorn, English Hawthorn Crataegus phaenopyrum Washington Hawthorn Crataegus punctata Dotted Hawthorn, Flat-topped Hawthorn Crataegus viridis Green Hawthorn,Southern Hawthorn Fraxinus americana White Ash, American Ash Fraxinus anomala Singleleaf Ash, Dwarf Ash Fraxinus excelsior Euopean Ash, Common Ash Fraxinus latifolia Oregon Ash Fraxinus ornus Flowering Ash Fraxinus oxycarpa Fraxinus oxycarpa Fraxinus pennsylvanica Green Ash Fraxinus quadrangulata Blue Ash Fraxinus sieboldiana Siebold Ash, Japanese Flowering Ash, Chinese Flowering Ash Hibiscus syriacus Rose, of Sharon Shrub, Althea Juglans ailantifolia Japanese Walnut, Heartnut Juglans californica California Walnut, Southern California Walnut Juglans cinerea Butternut Juglans microcarpa Texas Walnut, Little Walnut Juglans nigra Black Walnut Juglans regia English Walnut, Persian Walnut Malus 'Indian Magic' Indian Magic Crabapple Malus 'Prairifire' Prairifire Crabapple Malus 'Snowdrift' Snowdrift Crabapple Malus atrosanguinea Carmine Crabapple Malus brandywine Brandywine Crabapple Malus floribunda Japanese Flowering Crabapple Malus fusca Pacific Crabapple Malus hupehensis Tea Crabapple Malus pumila Apple Malus robusta Cherry, Crabapple Malus sargentii Sargent Crabapple, Pigmy Crabapple Malus transitoria Transitoria Crabapple Platanus acerifolia London Planetree Platanus mexicana Mexican Sycamore Platanus occidentalis American Sycamore, American Planetree Buttonwood Platanus racemosa California Sycamore, Western Sycamore Populus alba White Poplar European White Poplar, Silver Poplar Populus angustifolia Narrowleaf Cottonwood, Mountain Cottonwood Populus balsamifera Balsam Poplar Populus canescens Gray Poplar Populus deltoides Eastern Cottonwood Populus fremontii Fremont Cottonwood, Western Cottonwood Populus grandidentata Bigtooth Aspen Populus nigra Black Poplar Populus tremula European Aspen European Trembling Aspen European Quaking Aspen Populus tremuloides Quaking Aspen Populus trichocarpa Black Cottonwood Prunus americana Wild Plum American (Red) Plum August Plum, Goose Plum Prunus armeniaca Apricot Prunus avium Sweet Cherry Prunus besseyi Sand Cherry, Western Sand Cherry Prunus blireiana Blireiana Plum Prunus caroliniana Carolina Cherrylaurel American Cherrylaurel Prunus cascade Prunus cascade Prunus cerasifera Cherry, Plum Prunus cistena Purpleleaf Sandcherry Redleaf Sandcherry Cistena Sandcherry Cistena Plum Prunus dream Prunus dream Prunus emarginata Bitter Cherry, Wild Cherry, Quinine Cherry Prunus first Prunus first Prunus fruticosa Steppe Cherry, European Dwarf Ground Cherry, Mongolian Cherry Prunus glandulosa Dwarf Flowering Almond Prunus ilicifolia Hollyleaf Cherry, Holly-leaved Cherry Prunus laurocerasus Cherry Laurel Prunus lusitanica Portugal Laurel Prunus maackii Amur Chokecherry Amur Cherry, Manchurian Cherry Prunus mume Japanese Flowering Apricot Prunus newport Newport Flowering Plum Prunus okame Okame Flowering Cherry Prunus padus European Birdcherry Common Birdcherry Prunus prostrata Rock Cherry, Mountain Cherry Prunus sargentii Sargent Cherry, Sargent's Cherry Prunus serotina Black Cherry, Rum Cherry Prunus serrula Birchbark Cherry, Paperbark Cherry, Tibetan Cherry Prunus serrulata Japanese Flowering Cherry Prunus snow Prunus snow Prunus subcordata Klamath Plum, Sierra Plum, Pacific Plum Prunus subhirtella Higan Cherry Prunus subhirtella var. autumnalis Autumn Flowering Higan Cherry Prunus tai Prunus tai Prunus virginiana Prunus virginiana Prunus virginiana var. demissa Western Chokecherry Prunus virginiana var. virginiana Common Chokecherry, Eastern Chokecherry Prunus yedoensis Yoshino Cherry, Somei-yoshino Cherry, Tokyo Cherry Quercus phellos Willow, Oak Rhamnus alnifolia Alder Buckthorn, Glossy Buckthorn, Breaking Buckthorn Rosa acicularis Wild Prickly Rose Rosa gymnocarpa Little Wood Rose, Wood Rose, Baldhip Rose Rosa multiflora Multiflora Rose Rosa nutkana Nootka Rose Rosa pisocarpa Clustered Rose, Swap Rose Rosa rubiginosa Sweetbriar Rose, Eglantine Rose Rosa rugosa Rugosa Rose, Japanese Rose, Beach Rose Rosa woodsii Woods' Rose Salix alba Salix alba Salix babylonica Weeping Willow Salix caprea Salix caprea Salix integra Salix integra Salix magnifica Magnolia-leaf Willow, Magnificent Willow Salix matsudana Salix matsudana Salix pentandra Laurel, Willow, Bay Willow Salix phlebophylla Skeletonleaf Willow Salix purpurea Purpleosier Alaska Blue Willow Salix scouleriana Scouler's Willow Tilia americana American Linden, American Basswood Tilia cordata Littleleaf Linden Tilia euchlora Crimean Linden Tilia europaea European Linden, Common Linden Common Lime European Basswood Tilia mongolica Mongolian Linden, Mongolian Basswood Tilia tomentosa Silver Linden, Silver Basswood Ulmus americana American Elm Ulmus davidiana David Elm Ulmus davidiana var. davidiana unknown Ulmus davidiana var. japonica Japanese Elm Ulmus glabra Ulmus glabra Ulmus hollandica Dutch Elm, Holland Elm, Hybrid Elm Ulmus parvifolia Lacebark Elm, Chinese Elm Ulmus pumila Siberian Elm Viburnum dilatatum Linden, Viburnum, Linden, Arrowwood

Fall webworm is common throughout Western Washington, with one generation per year. Tents become conspicuous in August and September, particularly on black walnut, fruit trees, cottonwood, willow, and bigleaf maple. The mild maritime climate supports good overwintering survival of pupae. Most homeowners notice the unsightly webs and assume severe damage, but the pest is purely cosmetic on established trees. Physical removal of small tents in July, before they expand, is the most practical management for landscape trees.

— Chris Welch, ISA Certified Arborist

Sources & References

Primary: PNW Insect Management Handbook

Data Maturity
Structured Multiple sources. Expert review underway.