Invasive Species Management by Nature Stewards

 Amherst has numerous invasive plants. The five most common and most controllable are oriental bittersweet, autumn olive, common buckthorn, japanese knotweed and garlic mustard. Armed with the iNaturalist app and loppers, the Invasives Steward will identify, locate, record sightings and occasionally kill particular plants. 

Invasives grow best in sunlight; along roadways, trails, along meadow margins and in forest openings. The Invasives Steward will cruise town properties occasionally and be on the look-out for a single or a small cluster (small), a scattering of area patches (moderate) and a house-lot volume (huge) of invasives. Using your iNaturalist app, make an observation (photo) of the plant(s), get a species identification and (very important) type into the Notes box the word Invasive, your assessment of the amount (small, moderate or huge) and any other helpful comment. Save your observation.


Here's what happens in the background. Your observation with species name, photograph, location and your notes is saved to a very large database managed by the Cornell University. Observations can be displayed selectively within a named area like Amherst NH and any number of numerous filters selected -- like the word Invasive. Viewing a map of invasives with their location, type, photo and your notes allows the ACC to decide where, when and by whom to manage them. An individual or small patch can be dispatched by clipping with loppers or uprooting, bagged and disposed of as kitchen garbage. A moderate area can be managed by a work party or singly by an individual visiting multiple times. Huge areas will be dealt with by the ACC employing a commercial contractor.


One management factor is the proper time for removal or treatment; before reproduction berries or flowers appear.


  • Oriental Bittersweet: May – early June
  • Autumn Olive: July – August
  • Common Buckthorn: September – October
  • Japanese Knotweed: Any time; generally requires a few revisits
  • Garlic Mustard: Spring; first or second year


Identifying and managing invasive species (pictured above) is not hard. Follow the tips below.


Oriental Bittersweet has attractively colored fruit. As a result, it is eaten by mammals and birds, which excrete the seeds to different locations. Early detection is essential for successful conservation efforts. To reduce further growth and dispersal, above-ground vegetation killed.


Autumn Olive has grayish green leaves with silvery scales bottom side, and gives off a shimmery look. Stems are speckled, often with thorns. Bell-shaped cream or yellow flower clusters. Silvery fruit ripens to red. Autumn olive's nitrogen-fixing root nodules allow the plant to grow in even the most unfavorable soils. Fruit can be eaten raw or made into jam. Perform control efforts before fruiting to prevent the spread of seeds. Non-herbicidal treatments are to cut drill holes in the stump(s) and fill with Epsom Salts.


Common Buckthorn can be distinguished from native and other non-native buckthorns by its sharp, thorn-tipped branches and from native Hawthorns (Crataegus spp.) on which the thorns grow from the sides of branches. It also has noticeable forward-curved side veins on its leaves and clusters of purplish-black berries that have 4 hard seeds. Buckthorn seeds are easily spread by birds and other wildlife. It is fast growing and will reproduce from seeds or by stump sprouting. The seeds may remain viable in the soil for up to five years. It can quickly become a thicket crowding out all native vegetation. Non-herbicidal treatments are to cut and drill holes in the stump(s) and fill with Epsom Salts in the Fall.



Japanese Knotweed is an herbaceous perennial plant, meaning it dies back into the ground for winter before sprouting anew in the spring. It can grow between 3 feet and 8 feet tall on average with a bushy appearance. Its leaves are a medium green color, and it sports small white-green flowers in the late summer. The stems are knotted, bamboo-like. The roots are rhizomal and will easily spread. Severe infestations will require repeated attacks throughout the year. Beware that clippings can spread the plant -- dispose of them with care.


Garlic Mustard sends up a basal rosette of leaves in its first year. The leaves at this stage are roundish or kidney-shaped, with scalloped edges. The petioles (leaf steams) are often purple-tinged. When crushed, the leaves emit a distinct garlicy smell. In its second year, garlic mustard sends up a flower stalk, flowers typically appear in early May. The leaves become more triangular as they move up the stalk. The flower buds and flowers have a spicy, horseradish taste. When fully grown, garlic mustard can reach 2 or 3 feet. Garlic mustard starts going to seed around mid-May. As the plant flowers, seed pods form on the stem beneath. The seed pods are about 2 inches long and thin. They hold small black seeds, which have a spicy, horseradish taste. Control by weed-whacking before mid-May seeds form.