Invasive Plant Species
Purple Loosestrife
WARNING: INVASIVE PLANT SPECIES
INTRODUCTION: An invasive plant species — purple loosestrife — is taking up residence in Jackson. It has been spotted along the Wildcat at Eagle Mountain and close to the park as well as in private gardens. This is an invasive plant species and should be removed from where it is found and not used for garden plantings. Unfortunately, characteristics that make the plant a formidable invader — hardiness, tolerance of many moisture and nutrient regimes, and virtual freedom from insect pests and disease — also have made this plant an attractive garden perennial. Southern Living magazine stated, “Loosestrife is a perennial every garden needs. It’s stunning in leaf and flower, and grows just about everywhere.”
THE PROBLEM: However, purple loosestrife (Lythrum salicaria) is an aggressive invader of North American wetlands, lakes and rivers. Once established, purple loosestrife can become the dominant vegetation, forming monospecific stands which significantly reduce biodiversity and degrade habitat quality. Of primary concern is that purple loosestrife displaces native plants eliminating food and shelter for wildlife and other species. While strikingly colorful in flower, dense stands of loosestrife also impair recreational use of wetlands and rivers, impede water flow in drainage ditches and invade right-of-ways, requiring costly management efforts. Purple loosestrife is a widespread and serious problem, affecting both coastal and inland wetlands, lakes and waterways.
Purple LoosestrifeREMOVAL: The best way to remove purple loosestrife is by hand digging. Make sure that all pieces of root tissue are removed and dry out the plant material thoroughly before disposal. Root masses can be treated with a herbicide, such as Round-Up. Place all purple loosestrife plant material in a dark colored garbage bag and ensure that the bag is tightly secured to prevent it from spreading in the landfill area. Wherever permitted, plant material should be burned. For large scale infestations and when digging is not feasible, removing the flower head is an easy alternative. Cut off the top of the plant in midsummer before the flowers set seed. Monitor the dig site for a couple of seasons to ensure no new plants are growing and, if so, remove promptly.
BIOLOGICAL CONTROL: Three species of plant feeding beetles, Galerucella calmariensis, G. pusilla and Hylobius transversovittatus show promise as biological controls for purple loosestrife. Biological control is being introduced in the southern part of the state where the infestation is greatest.
FROM THE RSAs: The following exotic aquatic weeds, identified in “A Manual of Aquatic Plants” by Norman C. Fassett and “Aquatic and Wetland Plants of Northeastern North America” by Garrett Crow and C. Barre Hellquist, both copyrighted by The University of Wisconsin Press, shall be prohibited from being offered for sale, distributed, sold, imported, purchased, propagated, transported or introduced in the state, pursuant to RSA 487:16-a, because they pose a substantial threat to native species in the state: (h) Lythrum salicaria, L. virgatum, L. alatum and their cultivars, commonly referred to as purple loosestrife.
Japanese Knotweed
WARNING: INVASIVE PLANT SPECIES
INTRODUCTION: Japanese knotweed, a member of the buckwheat family (Polygonaceae), is an upright, shrublike, herbaceous perennial that can grow to over 10 feet in height. Although leaf size may vary, they are normally about 6 inches long by 3 to 4 inches wide, broadly oval to somewhat triangular and pointed at the tip. The minute greenish-white flowers occur in attractive, branched sprays in summer and are followed soon after by small winged fruits. Seeds are triangular, shiny, and very small, about 1/10 inch long.
ECOLOGICAL THREAT: Japanese knotweed spreads quickly to form dense thickets that exclude native vegetation and greatly alters natural ecosystems. It poses a significant threat to riparian areas, where it can survive severe floods and is able to rapidly colonize scoured shores and islands. Once established, populations are extremely persistent.
HABITAT IN THE UNITED STATES: Japanese knotweed can tolerate a variety of adverse conditions including full shade, high temperatures, high salinity, and drought. It is found near water sources, such as along streams and rivers, in low-lying areas, waste places, utility rights-of-way, and around old homesites. It can quickly become an invasive pest in natural areas after escaping from cultivated gardens.
Japanese knotweedBACKGROUND: Japanese knotweed was probably introduced to the U.S. in the late 1800’s. Also known as crimson beauty, Mexican bamboo, Japanese fleece flower, or Reynoutria, it was first introduced as an ornamental and has also been used for erosion control and for landscape screening. It is now found throughout the eastern U.S., in several western states, and Alaska, which has few exotic invasive plants to date.
CURRENT MANAGEMENT APPROACHES: Grubbing is effective for small initial populations or environmentally sensitive areas where herbicides cannot be used. Using a pulaski or similar digging tool, remove the entire plant including all roots and runners. Juvenile plants can be hand pulled depending on soil conditions and root development. Any portions of the root system not removed will potentially resprout. All plant parts (including mature fruit) should be bagged and disposed of in a trash dumpster to prevent reestablishment.
Cut stem treatment: Use this method in areas where plants are established within or around non-target plants or where vines have grown into the canopy. This treatment remains effective at low temperatures as long as the ground is not frozen. Cut the stem about 2 inches above ground level. Immediately apply a 25% solution of glyphosate (e.g., Roundup, or use Rodeo if applying in or near wetland areas) or triclopyr (e.g., Garlon) and water to the cross-section of the stem. A subsequent foliar application of glyphosate may be require to control new seedlings and resprouts.
Foliar spray method: Use this method to control large populations. It may be necessary to precede foliar applications with stump treatments to reduce the risk of damaging non-target species. Apply a 2% solution of glyphosate or triclopyr and water to thoroughly wet all foliage. Do not apply so heavily that herbicide will drip off leaves. A 0.5% non-ionic surfactant is recommended in order to penetrate the leaf cuticle, and ambient air temperature should be above 65 ºF.
