Spring Action Guide
SPRINGACTION PLAN
April–June is the highest-impact treatment window for nymphs. Miss it and you're managing adults all summer. Here's exactly what to do, week by week.
What's Happening in Spring
The SLF spring cycle runs on temperature, not the calendar. Here's how each month typically unfolds in DC, MD, and VA.
April
Hatch BeginningEgg masses begin hatching in warm years by late April. Tiny black nymphs appear on bark. This is still a critical window to scrape any remaining egg masses — once they hatch, scraping does nothing.
- Scrape any remaining egg masses immediately — deadline is early May
- Watch tree bark for tiny (~1/8") black nymphs with white spots
- Begin soil drench application of imidacloprid (takes 4–6 weeks to absorb)
- Scout Tree of Heaven and stream corridor vegetation
- Set up circle trap sites in advance of May deployment
Note: Assume all egg masses will hatch by May 1 — scrape now or lose the window.
May
Peak Nymph Season1st–3rd instar nymphs are in full force, primarily clustering on bark and stems of Tree of Heaven. This is the best month for systemic tree treatment and circle trap installation — trees are actively absorbing nutrients and drawing in systemics fast.
- Install circle traps on Tree of Heaven and high-value trees
- Apply systemic insecticide: dinotefuran (fastest uptake) or imidacloprid soil drench
- Spray nymph clusters with pyrethrin or neem oil contact spray
- Check and empty circle traps weekly
- Start logging sightings and kills at /my-kills
Note: Best systemic treatment window of the year — trees absorbing at maximum rate.
June
4th Instar Emerging4th instar nymphs — red with black and white patterning — appear late June in warmer years. Nymph populations are at their peak. Contact spray is highly effective. The systemic injection window is closing as summer heat slows uptake.
- Apply contact sprays directly on nymph concentrations (bifenthrin, pyrethrin)
- Maintain circle traps — peak capture rates this month
- Dinotefuran bark spray as a last-window systemic option
- Identify and map Tree of Heaven near you
- Watch for early adult emergence by late June in warmer areas
Note: Systemic injection window closing — act before July adult emergence.
Spring Action Priority List
Five actions, ordered by impact. Do them in this order.
Scrape Remaining Egg Masses
April onlyEvery mass still unhatched in April is a final chance. Once nymphs emerge, scraping does nothing. Each mass you destroy eliminates 30–50 nymphs before they ever feed.
Install Circle Traps
April–MayMount circle traps on Tree of Heaven and high-value trees before peak nymph emergence. Properly installed traps catch 50–200 nymphs per day at peak. Set early — nymphs are already moving by late April.
Apply Systemic Tree Treatment
April–May bestSystemic insecticides (imidacloprid, dinotefuran) move through the tree's vascular system and kill nymphs feeding on it. Spring is the best window: trees are actively absorbing. Imidacloprid soil drench needs 4–6 weeks lead time.
Start Tracking Sightings
NowSpring sighting data is valuable for researchers tracking the hatch timeline. Log your kills at /my-kills and report sightings at /map. Early data from your area helps calibrate treatment windows for the whole community.
Survey for Tree of Heaven
April–MaySpring is the best time to identify Tree of Heaven by its emerging compound leaves and distinctive smell. Identify and mark trees on your property and in your neighborhood — every ToH near you supports 3–5x higher nymph populations.
Treatment Timing Guide
Timing is everything. Some treatments must be done before the window closes.
Do NOW (April–May)
Systemic injection
Imidacloprid soil drench or dinotefuran bark spray — best uptake window
Circle traps
Install before nymph populations peak — set up by late April
Egg mass scraping
April only — any unhatched mass is still salvageable
Imidacloprid soil drench
Apply in April to allow 4–6 weeks for full uptake by June
Do in June
Contact spray
Bifenthrin or pyrethrin directly on nymph clusters at peak density
Dinotefuran bark spray
Fastest systemic option — still effective in June when soil drench window closes
Circle trap maintenance
Check weekly — peak capture rates in June
Nymph surveillance
Begin watching for 4th instar red nymphs and early adult emergence
What You'll See
Spring nymphs are easy to miss if you don't know what to look for. Here's what to expect at each stage.
Where to Look
Tree trunks
Base of Tree of Heaven trunks — nymphs aggregate low on the bark and walk upward
Stream corridors
Vegetation along streams and drainage ditches — ToH thrives in disturbed riparian zones
Wooden structures
Fences, wooden decks, and garden structures near ToH — nymphs disperse to any nearby surface
1st–3rd instar
~1/8"–1/2"Appearance
Black with small white spots arranged in rows. Legs are black. Move fast when disturbed.
Timing
Late April through May
Where
Bark of Tree of Heaven, stems of wild grapevine, wooden fences near stream corridors
4th instar (Red Phase)
~3/4"Appearance
Bright red body with black patches and white spots. Distinctive — unmistakable when you see one.
Timing
Late June (warm years), early July (typical)
Where
Same host plants but more mobile — seen on a wider variety of plants as they range further
Tree of Heaven — Spring Priority
Spring is the single best window to identify Tree of Heaven. Its compound leaves emerge distinctively in April and May, making ID faster than any other season.
Why Spring Is the Best ID Window
Distinctive emerging leaves
ToH leaflets emerge with a characteristic reddish tint in April. The large compound leaves (13–41 leaflets) are easy to recognize before the canopy fills in and they blend with other trees.
Gland-tipped teeth are visible
Each leaflet has 1–2 gland-tipped teeth near the base — the most reliable ToH ID feature. They're easiest to examine on new spring growth before leaves harden.
Act before nymphs commit
Nymphs aggregate on ToH as soon as they hatch. Treating or removing ToH in April reduces nymph load for the entire season before peak population builds.
Herbicide decisions
Spring is a good time for cut-stump treatment (after cutting) and basal bark treatment. Sap is running — systemics move effectively into the root system.
Spring ToH Actions
- —Survey your property and 100ft of adjacent land for ToH
- —Mark trees for treatment or removal decisions
- —Apply herbicide to small-diameter stems (basal bark or cut stump)
- —Remove ToH within 50ft of grapevines or high-value trees as priority
- —Do NOT cut mature ToH without applying herbicide — it will re-sprout aggressively from roots
Prepare for Summer
What you do in spring determines how bad your July is. Set up your tools now.
Related Guides
Spring Season Briefing
Weekly updates timed to the actual SLF hatch — know when to install traps, when to spray, and when the window closes. Free.