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Public Help Sought Identifying Invasive Stiltgrass and Perennial Pepperweed

Biologists from the Maine Department of Agriculture, Conservation, and Forestry (DACF) are asking for the public's help looking out for two severely invasive plants: Stiltgrass (Microstegium vinimeum) and Perennial Pepperweed (Lepidium latifolium). The plants are only known from a handful of sites in Maine, and the goal is to eliminate them from the state. The public can help by looking for the plants and reporting any suspected locations.

Stiltgrass is an annual grass that takes over the forest floor. Stiltgrass thatch builds up and makes it difficult for native trees, shrubs, and wildflowers to establish and grow. The thatch also raises fire risk. Infestations grow rapidly as each plant can produce up to a thousand seeds spreadable by moving water, deer, contaminated soil, dirty boots, or dirty equipment. Two locations of Stiltgrass were detected for the first time in Maine in 2020.

Perennial Pepperweed (aka Perennial Pepperwort) is an herbaceous plant that can take over sensitive habitats in salt marshes and sandy beaches. These are rare habitats in Maine and home to rare wildlife. When Perennial Pepperweed takes over, it can make the habitat unsuitable. Perennial Pepperweed can also grow in roadsides, riverbanks, and freshwater marshes. There are dense infestations of Perennial Pepperweed in Massachusetts, but only a handful of sites are known in Maine and New Hampshire.

What Can You Do?

The most valuable assistance is to review the MNAP Web Gallery and GoBotany website to become familiar with the plants and then email suspect photos and location descriptions to, or map the location with pictures in the online mapping tool iMapInvasives. This tool allows users to view other mapped locations, explore invasive species, and set up email alerts for areas or species of concern.

Newly detected Stiltgrass or Perennial Pepperweed should be removed to keep these invasive plants from damaging Maine's treasured forests and wetlands. DACF will offer support and guidance to affected landowners.

Helpful Video Resource

The Horticulture Program and the Maine Natural Areas Program (MNAP) recently released a short video about stiltgrass and how to identify it. Stiltgrass is known to spread to new areas on nursery stock; it is important that all nursery people be familiar with this plant to prevent its spread.

Key traits to identify Stiltgrass

  • Leaves are alternate along the stem, 2-4" long and 1/2" wide, pointed at both ends

  • Stripe of reflective hairs along the leaf midrib

  • Leaf edges and surfaces feel smooth to the touch

  • Trails along the ground, branching from nodes where it produces "stilts" (roots)

  • Shallow-rooted and easy to pull up

  • Flowers and sets seed late in the season (September-October); one to three seed spikes at the top of the plant that resemble crabgrass

  • Stems often develop a reddish tint late in the season

Key traits to identify Perennial Pepperweed

  • Leaves are alternate along the stem, lance-shaped, get smaller closer to the top of the plant

  • Lower leaves have gentle teeth around the edges; leaves higher on the stem may lack teeth

  • Stems are smooth and lime green, usually 1-4 feet tall, often multiple stems from one base

  • Small white flowers with four petals in dense clusters at the top of the plant (late June to late July); tiny fruits are reddish-brown, flat and disc-like

  • Roots have a strong smell like horseradish


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