Identification guide
Spring Invasive Plants Checklist: What to Look For in March, April, May and June
Spring invasive plants checklist: what to look for and act on each month from March through June, with links to species and removal guides.
Published Last reviewed
Spring is the narrow window when several invasive plants are easiest to see and easiest to stop before they seed. This checklist walks through March, April, May and June, with one action for each plant and a link to the detailed page.
The timing below comes from the extension and agency pages listed at the bottom of this page. Local weather can move each window by a week or two, so use the plant’s stage, not the calendar alone.
How to use this checklist
Identify the plant before you pull, cut or spray. Check your state rule before you move plants, soil or equipment. Then choose a method that matches the root system, bag every seed head and root fragment, and plan to come back.
Two safety rules come before everything else. Do not touch poison hemlock or giant hogweed. Poison hemlock is toxic if eaten, and its sap can irritate skin. Giant hogweed sap can cause severe burns when it meets sunlight. If you think a person or animal ate poison hemlock, call Poison Control at 1-800-222-1222, or 911 if the person has collapsed, is seizing or has trouble breathing. If giant hogweed sap gets on skin, wash it off with soap and water and keep the area out of the sun for 48 hours. Seek medical care if a reaction starts.
March: what to look for
| Plant | What to look for | Act now | Details |
|---|---|---|---|
| Lesser celandine | Tiny glossy leaves coming up in late February or March. Flowers follow in March and April. | Mark the patch. Treat while the leaves are green, from late March through early May. Do not mow. | Species profile · Removal guide |
| Garlic mustard | Low first-year rosettes of kidney-shaped leaves. Crush a leaf and smell garlic. | Pull the whole crown and taproot before the flower stalk rises. Bag anything in flower. | Species profile · Removal guide |
| Poison hemlock | First-year rosettes of fern-like leaves. The stem is still low. | Do not touch it bare-handed. Plan gloves, long sleeves and eye protection. Treat rosettes before they bolt. | Species profile · Removal guide |
| Japanese stiltgrass | Seedlings are germinating in late winter or early spring. | Apply a preemergence product by mid-March, or two to three weeks before germination. Do not dig the soil. | Species profile |
| Mile-a-minute weed | Seed is still in the soil; germination starts in early April. | Apply a preemergence product by mid-March, two to three weeks before germination. | Species profile |
| Callery pear | White flowers open before the leaves, usually in early spring. The smell is rancid. | Identify the tree and plan the removal. Basal bark and cut-stump work can be done now if the weather allows. | Species profile · Removal guide |
| Burning bush | One of the first shrubs to leaf out. | Check your state rule before buying or moving one. Foliar treatment starts in mid-May, but cut-stump and basal bark can be done now. | Species profile |
| Spotted lanternfly | Gray, putty-like egg masses on trees, brick, stone and outdoor furniture. | Finish egg-mass checks before hatching begins in late April in Pennsylvania. | Species profile · Hatch guide |
| English ivy | New growth on stems that survived winter. | Cut climbing vines at the base. Treat groundcover when new growth has two to four leaves. | Species profile |
| Japanese knotweed | New shoots are red or purple and tipped with furled, triangular leaves. | Do not cut and walk away. Plan the June cut and the late-season treatment. | Species profile · Removal guide |
April: what to look for
| Plant | What to look for | Act now | Details |
|---|---|---|---|
| Lesser celandine | Yellow flowers with 8 to 12 narrow petals. | Treat while the leaves are green. Do not mow. The window closes in early May in Pennsylvania. | Removal guide |
| Garlic mustard | White four-petaled flowers at the growing tip. | Pull before the seed pods form. Bag flowering plants; pulled plants can still make viable seed. | Removal guide |
| Poison hemlock | Rosettes are growing; some plants may start to bolt. | Treat rosettes before the flower stalks rise. Do not mow after flowers open. | Removal guide |
| Japanese stiltgrass | Small grass seedlings in lawns, trails and woodland edges. | Pull small patches. Postemergence treatment begins in mid-May. | Species profile |
| Mile-a-minute weed | Seedlings emerge in early April. | Pull seedlings before the barbs harden. Check the triangle leaf and circular sheath. | Species profile |
| Spotted lanternfly | Hatching begins late in April in Pennsylvania; New York and Massachusetts are mostly May and June. | Look for small black nymphs with white spots. Finish egg-mass checks. | Hatch guide |
| Callery pear | Full white bloom. The tree is easiest to spot now. | Identify it, then plan the cut and stump treatment. Do not cut and leave the stump. | Removal guide |
| Creeping charlie | Small lavender-purple flowers open from April to June. | Dig small patches, or treat actively growing plants with a lawn-labeled product. | Species profile |
| English ivy | New leaves are expanding. | Treat when new growth has two to four leaves. | Species profile |
| Burning bush | Leaves are fully out. | Foliar treatment starts in mid-May. Cut-stump and basal bark can be done now. | Species profile |
| Japanese knotweed | Shoots are elongating quickly. | Wait for the June cut. Cutting alone will not exhaust the rhizomes. | Removal guide |
May: what to look for
| Plant | What to look for | Act now | Details |
|---|---|---|---|
| Lesser celandine | Flowers are fading; the leaves are usually yellowing and starting to die back. | The window has usually closed by early May in Pennsylvania. Treat now only if the leaves are still green and actively growing, and do not mow. | Removal guide |
| Garlic mustard | Seed pods are forming on the flowering stems. | Pull and bag the plants now. Do not leave pods on the ground. | Removal guide |
| Poison hemlock | Tall stems are bolting; flowers open in June. | Treat before the flowers open. Keep skin covered, and do not use a string trimmer without protection. | Removal guide |
| Giant hogweed | Large carrot-family rosettes or bolting plants. In New York, flowers open in late June and July. | Do not touch it. Photograph it from a distance and report it to your state agency. | Species profile |
| Mile-a-minute weed | Vines are growing fast and covering shrubs. | Control before July 1. Bag seed-bearing vines. | Species profile |
| Japanese stiltgrass | Dense green mats in sun or shade. | Postemergence treatment runs from mid-May through August. Mechanical work can wait until June. | Species profile |
| Callery pear | Leaves are fully expanded. | Foliar treatment starts in mid-May and runs to the onset of fall color. | Removal guide |
| Burning bush | Leaves are fully expanded and the shrub is growing. | Foliar treatment starts in mid-May and runs to the onset of fall color. | Species profile |
| Spotted lanternfly | Black nymphs with white spots on new growth and vines. | Check tree of heaven, grapevines and smooth surfaces. Report finds outside the known range. | Species profile |
| Creeping charlie | Flowers and active growth. | Mid-spring to early summer is one of the two treatment windows. | Species profile |
| Multiflora rose | White five-petaled flowers open in late spring or early summer. | Mark the thicket now. Treat from midsummer to early fall, when the plant is moving food to its roots. | Species profile |
| Oriental bittersweet | Small greenish flowers open in late spring. | Cut vines now if you need to, but treat the regrowth no earlier than July 1. | Species profile |
| English ivy | New growth is still expanding. | Spring is the best window for foliar treatment. | Species profile |
| Japanese knotweed | Stems are tall and leafy. | Cut in June, then wait at least eight weeks before treating the regrowth. | Removal guide |
June: what to look for
| Plant | What to look for | Act now | Details |
|---|---|---|---|
| Poison hemlock | White umbrella-shaped flowers open from June into August in Pennsylvania. | Do not mow after flowers open. Bag cut material, and keep it away from children, pets and livestock. | Removal guide |
| Giant hogweed | Flowers open in late June and July in New York. | Do not touch it. Report it and let trained people handle the removal. | Species profile |
| Japanese knotweed | Stems are at full height. | Cut in June, then wait at least eight weeks before treating the regrowth. | Removal guide |
| Mile-a-minute weed | Vines are setting fruit; seed can begin forming in mid-June. | Finish control before July 1. Bag fruit-bearing vines. | Species profile |
| Japanese stiltgrass | Plants are still green and seed heads have not opened. | Cut or pull before seed set. Finish mechanical work before late August. | Species profile |
| Callery pear | Leaves are green and the tree is growing. | Foliar treatment continues. Cut-stump and basal bark remain options. | Removal guide |
| Burning bush | Leaves are green. | Foliar treatment continues. Cut-stump and basal bark remain options. | Species profile |
| Spotted lanternfly | Hatching continues through June in Pennsylvania. | Look for nymphs on new growth. Check tree of heaven and grapevines. | Hatch guide |
| Japanese beetle | Adults emerge in mid-June to early July in the Mid-Atlantic. | Handpick adults into soapy water. Do not use traps; they pull in more beetles. | Species profile |
| Multiflora rose | Flowers are fading and fruit is forming. | Mark the thicket. Treat from midsummer to early fall. | Species profile |
| Oriental bittersweet | Flowers are fading. | Cut vines if needed; treat regrowth after July 1. | Species profile |
| Garlic mustard | Seed pods are turning brown and brittle. | Bag the plants before the pods shatter. Do not compost them. | Removal guide |
What not to do in spring
- Do not mow lesser celandine. Penn State Extension says mowing can spread the plant and reduce how much herbicide the leaves absorb.
- Do not touch poison hemlock or giant hogweed. Wear gloves and cover your skin for hemlock, and leave giant hogweed to trained people.
- Do not cut tree of heaven and walk away. Cutting first triggers root suckers. Treat the standing tree from July to the onset of fall color, wait about 30 days, then cut.
- Do not cut Japanese knotweed and expect it to die. Cutting alone is not effective suppression. Use it as the first step before a late-season treatment.
- Do not spray on a windy or rainy day. The label sets the rain-fast window and the temperature limits.
- Do not move soil, seed heads or roots to another site. Bag them and follow your state and local disposal rules.
If you only do three things
- Stop the spring ephemerals first. Lesser celandine and garlic mustard are green for a short time, and both can set seed before summer.
- Protect yourself from the carrot-family plants. Poison hemlock and giant hogweed are health hazards, not just weeds.
- Put the summer work on the calendar. Mile-a-minute, stiltgrass, knotweed and the woody plants are not spring-only jobs. The July 1 mile-a-minute deadline and the June knotweed cut are the two dates most people miss.
Related WildScope pages
- When to treat invasive plants for the full seasonal calendar.
- How to get rid of invasive plants for the five-step overview.
- How to dispose of invasive plants for bagging seed heads and roots.
- How to get rid of invasive plants without chemicals for the non-chemical options.
- Removal guides for every species guide in one place.
- Invasive plants and invasive insects for the full species list.
Sources
Facts on this page were checked against the sources below. Each link shows the date the source was accessed.
- Lesser Celandine — Penn State Extension Accessed November 3, 2026
- Lesser Celandine — University of Maryland Extension Accessed November 3, 2026
- Garlic Mustard — Penn State Extension Accessed November 3, 2026
- Garlic mustard (Alliaria petiolata) — Wisconsin Department of Natural Resources Accessed November 3, 2026
- Poison Hemlock — Penn State Extension Accessed November 3, 2026
- Poison hemlock identification and control — King County, Washington Accessed November 3, 2026
- Callery Pear — Penn State Extension Accessed November 3, 2026
- Controlling Non-Native Plants in Ohio Forests: Callery Pear — Ohio State University Extension Accessed November 3, 2026
- Japanese Knotweed — Penn State Extension Accessed November 3, 2026
- Giant Hogweed — New York State Department of Environmental Conservation Accessed November 3, 2026
- Giant Hogweed: Identification and Control — Virginia Cooperative Extension Accessed November 3, 2026
- Japanese Stiltgrass — Penn State Extension Accessed November 3, 2026
- Invasive Plant Factsheet: Japanese Stiltgrass — University of Connecticut Integrated Pest Management Accessed November 3, 2026
- Mile-a-Minute — Penn State Extension Accessed November 3, 2026
- Invasive Plant Factsheet: Mile-a-minute — University of Connecticut Integrated Pest Management Accessed November 3, 2026
- Burning Bush — Penn State Extension Accessed November 3, 2026
- Controlling Non-Native Invasive Plants in Ohio Forests: Winged Burning Bush (Euonymus alatus) — Ohio State University Extension Accessed November 3, 2026
- Spotted Lanternfly Management for Homeowners — Penn State Extension Accessed November 3, 2026
- Spotted Lanternfly — USDA Animal and Plant Health Inspection Service Accessed November 3, 2026
- Ground Ivy — University of Maryland Extension Accessed November 3, 2026
- Managing Creeping Charlie in Lawns — University of Illinois Extension Accessed November 3, 2026
- Japanese Beetles in the Home Garden — Penn State Extension Accessed November 3, 2026
- Japanese Beetles on Trees, Shrubs, and Flowers — University of Maryland Extension Accessed November 3, 2026
- English Ivy — University of Maryland Extension Accessed November 3, 2026
- Controlling English Ivy in Urban Landscapes — NC State Extension Accessed November 3, 2026
- Multiflora Rose: Accurate Identification — Penn State Extension Accessed November 3, 2026
- Oriental Bittersweet — Penn State Extension Accessed November 3, 2026
- Oriental Bittersweet — University of Maryland Extension Accessed November 3, 2026
- Tree-of-Heaven — Penn State Extension Accessed November 3, 2026
- Tree-of-Heaven — University of Maryland Extension Accessed November 3, 2026
Related pages
-
Burning bush species profile
Burning bush identification: opposite leaves, corky winged twigs and bright red fall color. It is still sold in some states; check your state list first.
-
Callery pear species profile
Callery pear identification: white five-petaled flowers before the leaves, glossy wavy leaves and a rancid spring smell.
-
Creeping charlie species profile
Creeping charlie identification: square stems, opposite scalloped leaves and a minty smell, spreading by runners that root at nodes.
-
English ivy species profile
English ivy identification: lobed juvenile leaves creep and climb, while unlobed adult leaves flower and fruit. The vine stays green all winter.
-
Garlic mustard species profile
Garlic mustard identification: a first-year rosette, a second-year flower stem and a garlic smell when a leaf is crushed.
-
Giant hogweed species profile
Giant hogweed identification: deeply cut leaves, coarse stem hairs and white flower heads up to 2.5 feet wide. Its sap burns skin, so identify from a distance.
-
Japanese beetle species profile
Japanese beetle identification: a metallic green beetle with coppery wing covers and five white tufts on each side. Its grubs feed on lawn roots.
-
Japanese knotweed species profile
Japanese knotweed identification: hollow jointed stems, squared leaf bases and deep rhizomes. It resembles bamboo but has herbaceous stems.
-
Japanese stiltgrass species profile
Japanese stiltgrass identification: a silver stripe down the blade, shallow roots and late-summer seed heads. Learn how to stop it before it seeds.
-
Lesser celandine species profile
Lesser celandine identification: glossy leaves and eight to twelve yellow petals in early spring, usually gone underground by late May.
-
Mile-a-minute weed species profile
Mile-a-minute weed identification: triangular leaves, a saucer-shaped sheath and backward barbs on the stem. Learn how to stop this annual vine before seed set.
-
Multiflora rose species profile
Multiflora rose identification: fringed stipules at the leaf base, white five-petaled flowers and arching thorny canes that form dense thickets.
-
Oriental bittersweet species profile
Oriental bittersweet identification: twining stems, glossy leaves and yellow-orange fruit that splits to red. Fruit grows along the stem, not just at the tips.
-
Poison hemlock species profile
Poison hemlock identification: a smooth, hollow stem with purple blotches and fern-like leaves. All parts are toxic if eaten; wear gloves when handling.
-
Spotted lanternfly species profile
Spotted lanternfly identification: gray black-spotted forewings held roof-like, red hindwings and a yellow banded abdomen. Egg masses look like gray putty.
-
Tree of heaven species profile
Tree of heaven identification: long compound leaves with smooth edges and a gland at each leaflet base, pale bark and a strong odor when crushed.
-
Identification guides
Browse every published guide in this category.