Japanese Knotweed-- Biology, Impacts, and Control Brock Woods, Wisconsin Dept. of Natural Resources and Univ. of Wis. Extension—with help from Oneida Co. LWCD “The Worst Invasive Plant in the World”? Polygonum cuspidatum (Fallopia japonica; Reynoutria Japonica) P. cuspidatum internationally recognized F. japonica most used in Europe R. japonica being used less recently Mexican Bamboo, Japanese Fleeceflower, Crimson Beauty Distribution and Spread From Japan, Chinas & Korea where it invades newly exposed soils Into Europe in 1840s US East coast in 1869? Wisconsin ~1960 In at least 42 states Plant sales Description: An exotic, semi-woody perennial fruit leaf Stalk Node Rhizome flowers Roots Leaves Simple, alternate Oval to triangular, 3-4” wide, 4-6” long Flat base, narrows to a point Upper dark green, under light green Petioles long Stems 6– 12 feet tall Thick, erect, smooth, hollow, round, swollen nodes Green and reddish brown Bamboo-like, arching Killed by frost but stems stay upright through the winter Dead stems can be a fire hazard Stems turn rusty in fall making winter a great time to note plants Root System Tap root often 2-3 meters deep Horizontal rhizomes to 20 meters Rhizomes and fibrous roots become large & massive Will grow under roads, break brick walls & pavement Flowers Small, cream to light green, plume-like clusters Upper part of leaf axils near ends of stems Functionally dioecious Male flower stems erect, female flower stems droop? Blooms Aug-Sept Fruit and Seeds 3-winged fruit Seeds small, shiny black, triangular Up to 130,000 per stem 7 million seeds per plant of 10 stems Easily transported by wind and water Seeds live 1 to 4 years? Reproduction—still evolving Asexual through root, rhizome, and stem fragments in or on moist soil Sexual through both intra-species fertilization and inter-specific fertilization with P. sachalinense (giant knotweed) to produce hybrid P. x bohemicum (Bohemian knotweed) Hybrid vigorous and common, with introgression back to parent plant Suggests enhanced reproduction over time, making targeting hybrids for elimination wise Some research suggests both male and female plants in most patches making functional seed common Unclear if this is true in the Midwest So-called Sterile Hybrids Male garden varieties such as Variegated Knotweed can pollinate wild female plants, thus producing seed Bann them? Polygonum sachalinense Leaves & Flowers Leaves are larger, with distinct, long, multicellular hairs on underside midrib (bumps on P. cuspidatum) Leaf bases are deeply cordate Inflorescences are smaller, shorter P. x bohemicum traits are intermediate P. sachalinense (AKA Giant or Sakhalin Knotweed) P. cuspidatum Seedlings Research on germination is mixed May have no germination requirements at all May need cold period Requires light and moist soil Few to 10,000s/ sq. m Seedlings found in Madison, Wisconsin Vegetative dispersal mechanisms Moving contaminated soil Flooding carries broken pieces of rhizomes/stems downstream Mowing without collecting plant parts Buying it as an ornamental Trades Plant Growth and Form 1 to 3.3 inches/ day Documented patches up to 16 acres Patches often round mound shaped Along water and roads patches often linear— 10 meters wide and hundreds of meters long Typical Patch Forms JK clone in Oneida Co., Wis. JK on Hwy 51, Vilas Co., Wis. Habitats Upland, wetland, shoreline, hillsides, roadsides, yards, woodland edges Prefers sun, but tolerates shade Moist soil to germinate or grow roots Many types of soils Variety of Habitats Impact--Why Worry? Threat to native plant and animal communities Reduces light Allelopathic; possible other soil changes Eliminates native plants and reduces biodiversity Very little wildlife habitat value: cover Web: “Life on the Japanese Knotweed” Poor erosion control; ground cover absent and poor surface root system Increases siltation Suspect trout populations impacted Japanese Knotweed in the UK Causes Ecological and Infrastructure Damages Effects on Infrastructure Costs UK $2 to 10 million per year “One of the worst IS along UK’s 2200 miles of canals and rivers” Mortgages refused “Capable of pushing through concrete, posing a risk to the structure and fabric of the building” (typical loss $10,000) Safety compromised: signs obscured and guard rails covered Will these problems occur here? Control / Management Very difficult if not impossible to eradicate once established Large stands are difficult to manage & keep under control Crucial to start control as soon as it appears Typically takes multiple treatments over several years, depending on size & control methods – don’t expect immediate results! Landscape scale strategy best for long-term control Typical types of Control Manual/Mechanical Pulling, digging, cutting, mowing Covering Chemical Foliar Stems Biological Goats Combinations Control in the UK Landowners increasingly required by law to be responsible for removing their JK Herbicides Bury contaminated fill on site (at least 2 meters) Fill dump—pay to put their fill elsewhere “Spoil to Soil”—removing all contaminated soil, treating with heat or other means and returning it 10 year guarantees typical Choice of Treatment Method Herbicide or Manual/mechanical: Cut mow Pull Dig Cover Control Manual – Mechanical Small stands, new Not generally plants recommended but may be Mowed and/or cut effective on very small Needs to be done plants regular, short-term Beware root fragments basis Difficult to remove the Nearby stand? entire root Years of cutting to weaken rhizomes Heavy machinery for enough to kill it massive roots? Collect all pieces: Covering Heavy duty black plastic or geo textile fabric Better in open areas, on smaller patches Often 3 or more growing seasons Cut old stems, cover a minimum of 7 ft beyond existing stand Leave cover loose but anchor with rocks or cement blocks Watch for holes from new growth or other objects Eliminate new growth every few weeks by stomping and clean debris Best if done in spring before growth takes place Later in the year should be cut several times during the season beforehand Chemical Application The most effective control method for now Several methods to choose from Pre-emergence Foliar spray or wipe Stem: pour inject Follow label directions Acquire permits Foliar Spray Treatment Late summer application (before a killing frost) Sugars to the rhizomes for storage will take the herbicide along Combine with cutting in June If done carefully: less contact with the soil & less risk of injury/kill of non targeted plants thru root systems Non-selective herbicides; take care Stem Injection | Cut & Pour Only glyphosate is labeled Glyphosate is used for the for stem injection cut & pour Highly effective Cut stems between the Use injection gun lowest two nodes Labor intensive especially Pour measured amount in large dense stands each hollow stem Stems >1/2 inch Labor intensive Prevents drift Follow directions on label for application rate Needs to be repeated Best in late summer, early fall Prevents drift Choice of Chemical, Timing & Rate See handouts for suggested herbicides and application rates Follow directions!! Read the labels!! Use caution!! Keep children and pets away from the site!! Timing depends on methods, but herbicides almost always best used late in the season Dispose of all Plant Parts Properly Do not compost stems, rhizomes and/or roots; discard with trash or burn Care with seeds Keep all parts of JK out of waterways, wetlands, or other wet sites! Biological Control Goats will eat foliage Not always feasible Control on a lands with acreage Graze several times a season over many years Other biocontrol is still being researched and not yet available Two possible biocontrol organisms: an insect and a fungus Aphalara itadori (psyllid) What can we expect from biocontrol? Long term approach to weed control; major results likely to take years. Control, not eradication, is the end point Target weed reduced to an acceptable level should reduce costs Anticipate attacked knotweed plants will have reduced vigor, allowing neighboring plants to re-establish thanks to reduced competition. What we should not expect is the complete abandonment of current treatments Natural enemies should be seen as part of an integrated control programm, not the complete solution. Testing Potential BC Organisms Goldenrod Restoration Critical; often neglected Fast growing, possibly aggressive, native species Needs research Some examples: willow (Salex sp), aspen (Populus sp), red maple (Acer rubrum), dogwood (Cornus sp), goldenrod (Solidago sp), hyssop (Agastache sp), native grasses, etc. Dogwood Nurse crop of annual rye, buckwheat, or other annual cover crop waterways and other erodible areas Poplar Into the Future? Research needed Testing being done on soil steaming, injecting steam in the contaminated soil to kill plant parts Support Biological control research now Eradication is not a likely option in the future Education & management may be the key to minimize this plant Resources for this presentation Invasive Knotweed BMP, January 2008, King County DNR, www.kingcounty.gov/weeds Invasive Plants of the Upper Midwest, An Illustrated Guide to Their Identification and Control. Elizbeth J. Czarapata Japanese Knotweed: Facts, Discussion Forum, and Encyclopedia Article. www.absoluteastronomy.com/topics/Japanese_Knotweed 2010 Pacific Northwest