National Snapshot

Honeydew, hungry caterpillars, and scorch that lies

High summer settles in. Sap-feeders are the dominant nuisance — magnolia scale and the soft scales are dripping honeydew and blackening foliage with sooty mold, while spotted lanternfly adults spread onto woody trees. Late-summer caterpillars (orangestriped oakworm, yellownecked, walnut caterpillar) are defoliating oaks and maples, and spider mites hold at their peak in the heat. The tricky part this week is diagnostic: bacterial leaf scorch, oak wilt, and plain drought are all browning canopies at once, and they call for opposite responses.

Sap feeder

Magnolia & soft scales are the honeydew story — mature magnolia scale females are conspicuous now, with cottony camellia and lecanium scale close behind. Sooty mold and wasps follow. Crawlers emerge late August: plan the treatment window now.

Caterpillar

Late-summer defoliators are out — orangestriped oakworm and greenstriped mapleworm on oaks and maples, plus yellownecked and walnut caterpillars, while fall webworm nests grow large and conspicuous.

Invasive

Spotted lanternfly adults are widespread and feeding on woody trees, coating surfaces in honeydew and drawing yellowjackets. They'll begin laying egg masses in late September — scout and report.

Mite

Spider mites remain at their seasonal peak in the heat and drought — two-spotted, oak, spruce, and honeylocust mites bronze foliage, worst on dusty, water-stressed canopies.

Disease

Scorch look-alikes: bacterial leaf scorch, oak wilt, and drought scorch all brown the canopy in August with opposite fixes (see the alert below). Tar spot, Cercospora, and anthracnose are also climbing.

Borer

EAB & clearwing borers — EAB flight is winding down but larvae keep tunneling; deep-water stressed trees, avoid wounds, and keep ash material and firewood local.

Methodology Note

How we report growing degree days

Growing degree days accumulate from January 1 and only climb through the season. Each region's reading is anchored to the latest measured cooperative-extension station data (base 50°F), so figures track real, on-the-ground heat rather than the calendar. Because published station data can lag by a week or two, always confirm against your nearest local station (NEWA, Enviroweather, or your state tool) before timing an application.

Pest on the Chart · This Week

Magnolia Scale

Neolecanium cornuparvum

This week's pest on the chart — the largest soft scale in the region and its reigning honeydew champion. Mature females (up to half an inch, shiny brown often dusted with white wax) are conspicuous on the twigs of magnolia and occasionally tuliptree right now, dripping honeydew that blackens foliage and hardscape with sooty mold and draws wasps and ants. Heavy infestations cause branch dieback and thin, off-color canopies. The vulnerable life stage is the crawler, which emerges late August into September.

Crawlers

Late Aug–Sep

Top Hosts

Magnolia

Rx Note

Time to crawlers

℞ — The window that matters is crawler emergence, late August into September. Monitor twigs with double-sided tape and treat at first crawler with horticultural oil, repeating per label; an insect growth regulator such as pyriproxyfen or buprofezin timed to crawlers gives strong, selective control. Conserve the lady beetles and parasitoids already working the colony, and wash honeydew and sooty mold from high-visibility trees. Mark the calendar now so the window isn't missed.

Diagnostic Watch

Leaf Scorch Look-Alikes

Three very different problems all brown the canopy in August — and the fixes are opposite. Read the pattern before you write the prescription.

Bacterial Scorch

Bacterial leaf scorch (Xylella) — chronic and recurring, same branches worsening year to year. Marginal browning with a yellow or reddish band between the dead and green tissue. Confirm by lab; no cure — support vigor, and oxytetracycline injection can suppress symptoms on high-value trees.

Oak Wilt

Oak wilt (Bretziella) — fast — red oaks wilt and drop leaves top-down over weeks, browning from the margin/tip inward, sometimes with fungal mats. Confirm by lab, break root grafts, remove red oaks, and protect high-value oaks with propiconazole. No new county confirmations this week beyond the recent Monroe Co., NY and Arlington, TX finds.

Drought Scorch

Drought scorch (abiotic) — uniform marginal browning across the whole tree at once — no color band, no vascular streaking. Tied to the current severe Northeast drought and hot, dry sites; responds to deep, slow watering.

℞ When the pattern is unclear, sample for lab confirmation before committing to a plan — oak wilt and bacterial leaf scorch diverge sharply, and neither responds to the watering that fixes drought scorch. And don't wound oaks: the oak-wilt risk window runs into September in the North.

Regional Rx · 5 Zones

Read your zone like a chart

Each card reports the region's growing-degree-day reading (the vital sign that drives every timing call), what's active now (Diagnose), and how to time treatment (℞). GDD ranges are typical for the week, base 50°F from Jan 1 — always confirm against your nearest station.

NE

Northeast & New England

ME · NH · VT · MA · RI · CT · NY

GDD · Accumulated

~1,450–1,850

0

1,500

3,000+

Conditions: Accumulation advancing from a July 8 UMass base of ~1,094 (base 50°F). Drought is now severe on the Cape and significant across much of the state — crispy, unirrigated landscapes and premature leaf drop are widespread.

Diagnose · Active Now

•

Magnolia scale females conspicuous with heavy honeydew; cottony camellia & lecanium scale active.

•

Spotted lanternfly adults on tree-of-heaven and grape; box tree moth 2nd-gen larvae spreading on the Cape.

•

Fall webworm nests enlarging on tupelo and sweetgum; late-summer caterpillars beginning.

•

Two-spotted & oak spider mites at peak in the dry heat.

•

Drought scorch widespread; Pseudocercospora leaf blotch recurring on lilac.

℞

Prescribe · Timing & Materials

•

Magnolia / soft scale: mark late August for crawler-timed horticultural oil (repeat per label) + an IGR; hose off honeydew.

•

Fall webworm & caterpillars: prune out small nests; Btk / spinosad on young larvae; tolerate on large, healthy trees.

•

Mites: rinse dust, use a selective miticide only if damaging, and protect predators.

•

Drought: deep-water high-value trees; confirm by lab before treating scorch, and defer oak pruning (oak-wilt window runs into September).

MA

Mid-Atlantic & DMV

NY · NJ · PA · MD · DE · DC · VA · WV

GDD · Accumulated

~2,100–2,650

0

1,500

3,000+

Conditions: Warm and humid with high foliar-disease pressure. SLF adults are heavy in central Maryland — Baltimore City and the central counties (Howard, Baltimore, PG, Montgomery, Carroll, Frederick, Washington) remain the most infested — and are now visiting trap trees.

Diagnose · Active Now

•

Spotted lanternfly adults heavy on woody trees and trap trees; honeydew, sooty mold, and yellowjackets.

•

Magnolia scale honeydew; crapemyrtle bark scale + aphid sooty mold.

•

Orangestriped oakworm & yellownecked caterpillars; fall webworm nests enlarging.

•

Sycamore & oak lace bugs stippling (heavy reports around Sharpsburg); spider mites in the heat.

•

Bacterial leaf scorch symptoms emerging on oaks, elms, and sycamore.

℞

Prescribe · Timing & Materials

•

Spotted lanternfly: scout and report; treat tree-of-heaven trap trees so visiting adults are killed; band saplings. Adults feed mainly on woody trees.

•

Magnolia scale: time horticultural oil + IGR to late-August crawlers.

•

Caterpillars: prune webworm nests, Btk on young larvae; handpick oakworm clusters.

•

Lace bugs: hort oil / insecticidal soap to leaf undersides on nymphs.

•

Bacterial leaf scorch: confirm by lab; no cure — support vigor with water and mulch, and consider oxytetracycline trunk injection for high-value trees.

SE

Southeast

NC · SC · GA · TN · AL · MS · FL · VA

GDD · Accumulated

~2,800–3,800

0

1,500

3,000+

Conditions: Hot and humid; the season's furthest along with a heavy honeydew and sooty-mold load. Late-summer caterpillars are defoliating oaks and maples.

Diagnose · Active Now

•

Crapemyrtle bark scale + crape myrtle aphid driving heavy sooty mold.

•

Orangestriped oakworm defoliating pin and willow oaks (heavy frass); greenstriped mapleworm on maple.

•

Fall webworm large nests; yellownecked caterpillar; oak & azalea lace bugs stippling.

•

Gloomy & obscure scale on maple and oak; southern red spider mite in the heat.

•

Cercospora leaf spot & powdery mildew on crape myrtle; borers on stressed pines.

℞

Prescribe · Timing & Materials

•

Crapemyrtle bark scale: systemic imidacloprid / dinotefuran drench timed to avoid bloom for pollinators, IGR at crawlers, dormant hort oil; wash off sooty mold.

•

Caterpillars: tolerate on large trees; handpick oakworm clusters; prune webworm nests or Btk on young larvae.

•

Lace bugs: hort oil / insecticidal soap on nymph undersides.

•

Crape myrtle disease: resistant cultivars, airflow, labeled myclobutanil / propiconazole.

•

Borers: stress reduction and sanitation; do not move infested wood.

MW

Midwest & Great Lakes

OH · MI · IN · IL · WI · MN · IA · MO

GDD · Accumulated

~1,900–2,500

0

1,500

3,000+

Conditions: Development is running ~2 weeks ahead. Japanese beetle feeding is tapering; hot, dry pockets keep spider mites active near dusty margins. Use MSU Enviroweather / GDDTracker for local timing.

Diagnose · Active Now

•

Magnolia scale females conspicuous — crawlers expected late August.

•

Japanese beetle tapering; emerald ash borer flight winding down as larvae tunnel.

•

Fall webworm nests enlarging; bagworm larvae now large in the southern Midwest.

•

Walnut & yellownecked caterpillars; spider mites flaring in dry pockets.

•

Oak wilt risk — warm-season oak wounds invite sap-beetle vectoring.

℞

Prescribe · Timing & Materials

•

Magnolia scale: plan late-August crawler-timed horticultural oil + IGR; hose honeydew.

•

EAB: systemic trunk injection (emamectin benzoate) for high-value ash on cycle.

•

Oak wilt: do not prune oaks now; paint any unavoidable wounds immediately.

•

Webworm / bagworm: prune webworm nests; use chlorantraniliprole for large bagworm.

•

Japanese beetle: tolerate late feeding; treat only high-value specimens, minding bloom.

W

West & Pacific

CA · OR · WA · NV · AZ · CO · UT · ID · MT

GDD · Accumulated

Highly variable

Coast / high elev.

—

Inland / low desert

Conditions: Wide range by elevation and coast vs. inland; irrigation-driven stress is the key variable and fire season is in full swing across the interior West.

Diagnose · Active Now

•

Wood-boring beetles on stressed trees — invasive shothole borers in SoCal urban forests, goldspotted oak borer on oaks, Mediterranean oak borer.

•

Emerald ash borer in Oregon — five Willamette Valley counties remain under quarantine (Washington, Yamhill, Marion, Clackamas, Multnomah).

•

Spider mites at peak in heat and road dust; aphids with honeydew and sooty mold.

•

Bacterial blast / canker on stone fruit and citrus; yellowjackets building.

℞

Prescribe · Timing & Materials

•

Borers: deep-water summer-rainfall-adapted trees, avoid fresh wounds, and do not move ash material or firewood; in EAB zones, inventory ash and consider systemic protection, then report.

•

Spider mites: rinse dust, use hort oil or a selective miticide only if damaging; protect predators.

•

Aphids: strong water spray, conserve natural enemies, tolerate on established plants.

•

Stone-fruit canker/blight: prune out in dry weather, cutting several inches into healthy wood.

•

Fire: maintain defensible space and thin fuel ladders around trees and structures.

Field notes — read before you spray

Sample before you treat the scorch. Bacterial leaf scorch, oak wilt, and drought all brown the canopy now — and the fixes are opposite. Confirm by lab when the pattern is unclear.

Time scale to the crawlers. Magnolia and soft-scale females are obvious now, but oil and IGRs work on the crawlers emerging late August — monitor twigs with tape and mark the calendar.

Don't move wood. EAB and oak wilt travel on firewood — keep ash material and unseasoned oak local, and hold off on oak pruning into September.

Sources · Cooperative Extension & USDA

Compiled from public reporting by land-grant cooperative extension services and USDA partners, including UMass Extension Landscape Message & Insect/Mite Almanac; University of Maryland Extension IPMnet & Maryland Dept. of Agriculture; Rutgers Plant & Pest Advisory; NC State Extension, Clemson HGIC & UGA; Michigan State University Extension, Iowa State & UMN; UC Statewide IPM Program; Oregon Dept. of Agriculture / ODF EAB program; and USDA NIFA / USDA Forest Service cooperative forest-health programs. Regional summaries are paraphrased; consult the original bulletins and your local extension office for specifics.

Manage fall webworm, mites, and SLF with region-specific pest control advice.

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