Updated: August 10, 2023

Bradford, callery, or ornamental pear (Pyrus calleryana)

Developed as a sterile cultivar or clone, the Bradford’s collapsing branch structure led to the introduction of more hybrids. Cross-pollination resulted in fertile offspring with berry-sized fertile fruit. It spreads rapidly to disturbed and natural areas, displacing natives and disrupting natural succession. Seedlings may grow long thorns. P/D, WW, G, C&P/S, C&G - see key below

Empress or princess tree (Paulownia tomentosa)

Highly valued in Asia, here its fast growth rate makes wood worthless for export. It invades through its winged seeds (up to 20 million a tree) and persistent suckering from stump or roots. Requires some sun, otherwise highly competitive. P/D, F/S, G, H&S, C&P/S, C&G, PostE -see key below

Mimosa (Albizia julibrissin)

Native from Iran to Japan, the “silk tree” was introduced for its ferny foliage, pink summer flowers, and fast maturity. Pods produce high seed volume, viable up to 50 years. A nitrogen-producing member of the pea family, it can flourish in poor, disturbed soils. Needs some sun. It is primarily a threat to meadows and along water and roadways. It will re-sprout. P/D, G, H&S, C&P/S - see key below

Norway maple (Acer platanoides)

Large Eurasian tree prized for its round symmetrical canopy. Its extremely dense shade and root competition suppress most growth underneath, except its own seedlings. Milky sap distinguishes it from sugar maples, which it out-competes and pushes out of its ecological niche. Its helicopter-type samara seeds, typical of maples, are horizontal rather than hanging. Leaves turn yellow in late fall. Its shade-tolerant seedlings out-compete natives and create monocultures. P/D, C&P/S, H&S, G - see key below

Sawtooth oak (Quercus acutissima)

This Asian oak produces acorns at a much earlier age than native oaks. Planted for wild game, it outcompetes native oaks. Leaves are entire, unlike most lobed oak leaves, with spine-tipped serrations. The acorn cap is shaggy. Treat re-growth and replace with native oaks. P/D, PostE, G, C&G, C&P/S, H&S - see key below

Siberian elm (Ulmus pumila)

This Asian elm was promoted to replace American elms killed by Dutch elm disease. (Disease-resistant American elms are now available.) Rapid growth and copious seeds enable it to flourish in tough conditions and disturbed soils, ironically displacing American elms. It inhibits growth under its canopy. Often confused with other trees, key identifiers are small leaves (1 to 2 1/2 inches), even leaf base, and single serrations, unlike the double serrations of our native American elm and slippery elm. P/D, C/M&reC, C&G, C&P/S, G, H&S, WW - see key below

Tree of heaven (Ailanthus altissima)

This fast-growing native of China grows in the worst conditions. Crushed leaves and all other tree parts have a rank odor described as “rotten peanut butter.” It is often confused with desirable native trees. Long compound leaves resemble walnut, but walnut bark is coarse and fissured. Its smooth gray bark resembles sumac but has prominent leaf scars. Yellow-green flowers on female trees produce papery samara seeds in large numbers, late summer to early fall. Seed clusters turn brown and hang through winter. Root toxins kill competing plants. Suckers create monoculture colonies. Mere cutting cannot control it; rather cutting stimulates a multitude of new sprouts. P/D youngest only—get all fragments, H&S (no more than a one inch gap between cuts), PostE (spray re-growth). Also, in February or March apply triclopyr or Garlon® to the lower trunk bark. - see key below

White mulberry (Morus alba)

Introduced from Asia in the colonial period as food for silkworms in an attempt to start a silk industry, white mulberry hybridized with our native red mulberry (which had better fruit) and transmitted a fatal root rot. It has both lobed and unlobed leaves, whereas red mulberry only has unlobed. Invades natural areas. P/D, C/MreC, G, C&P/S, C&G - see key below

Key for control methods

Mechanical options

  • (B) Burn: Use controlled fires to destroy aboveground growth. (First, contact local fire department).
  • (C&G) Cut and grind:  Cut down, then grind stump.
  • (C/M/reC) Cut, Mow, and Re-cut:  Cut to the ground and re-cut at the first appearance of new growth.  This starves the root system. It may require persistence.
  • (F/S) Flower/Seed removal:  Do not allow seed development.  When plant removal must be postponed, prevent spread by seed. Cut off flowers before seed forms. Some plants flower and produce seed at the same time. Bag and dispose of seeds in landfills.  DO NOT compost.
  • (G) Girdle:  Remove bark and cambium layer.  Remove (or spray) any re-sprouting from roots or below girdled area.
  • (P/D) Pull/Dig: This is especially effective with seedlings or annuals. Mile-A-Minute vine, for instance, has almost no root system at all.  However, for those that can re-sprout from a tiny root piece, such as Canada thistle, removal of entire root is critical. Moist soil facilitates.
  • (SM) Smother: Cover plants with cardboard, many layers of newspapers, or plastic, then mulch. Plastic must be removed afterward, and if mulch decomposes on it, this can be an arduous process.
  • (WW) Weed Wrench (TM):  This tool can uproot large shrubs and small trees

Chemical options

  • (C&P/S) Cut and Paint or Spray:  Cut down the trunk and paint or target spray the stump within five minutes.
  • (H/S) Hack & Squirt:  Slash bark using a saw or hatchet, and squirt liquid herbicide into the wounds; re-spray any re-growth. 
  • (PostE) Post-emergent herbicides:  Spray foliage of perennial/woody plants. Spot-treat in lawns.
  • (PreE)Pre-emergent herbicide:  Spread this granular herbicide prior to seed germination. 

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