HPIPM:Prostrate knotweed

Taxonomy

Domain	Eukarya
Kingdom	Plantae
Phylum	Magnoliophyta
Class	Magnoliopsida
Superorder	Caryophyllanae
Order	Caryophyllales
Family	Polygonaceae
Genus	Polygonum

Scientific Name

Polygonum aviculare

Common Name

prostrate knotweed

Prostrate knotweed (Polygonum aviculare)

Compiled by Melissa Graves, and Marjolein Schat, Montana State University from the following sources:

http://plants.usda.gov/java/profile?symbol=POAV

http://www.ontarioweeds.com/weed.php?w=POLAV

http://www.ppws.vt.edu/scott/weed_id/polav.htm

http://akweeds.uaa.alaska.edu/pdfs/species_bios_pdfs/Species_bios_POAV.pdf

Identification and Life Cycle

Prostrate knotweed (Polygonum aviculare) is a non-native annual in the Buckwheat (Polygonaceae) family. Cotyledons are linear in outline and are often misidentified as a grass seedling. The stem below the cotyledons (hypocotyl) is often reddish in color. Prostrate knotweed has a taproot. The lanceolate leaves are arranged alternately along the stem. Each leaf has a short petiole and is approximately 1/2 to 1 1/4 inches long and up to 1/3 inch wide. Stems are branching, growing prostrate along the ground, and range from 4 to 24 inches in length. Stems are swollen at the nodes with a thin membranous sheath (ocrea) encircling the stem at each leaf base. Flowers occur in the leaf axils, between the stems and leaves. The flower clusters contain between 1 and 5 inconspicuous, white to pinkish-white flowers. The fruit is a dark red to brown achene.

Habitats

Prostrate knotweed prefers a habitat with full sun and a heavy soil that is slightly moist to dry. This species flourishes in poor soil where there is little competition from other plants. It can withstand a fair amount of trampling. Habitat preferences include road and driveway edges, cracks in sidewalks and pavement, compacted soil along paths, and waste areas with barren ground.

Impacts

Prostrate knotweed quickly covers bare soil and may prevent native species from establishing on the site. Additionally, this species is a host for number of fungi, viruses, and nematode species.

Biology and Ecology

Prostrate knotweed is one of the earliest germinating summer annual weeds. This species reproduces by seed. Most seeds of prostrate knotweed are dormant and germinate in spring after a moist chilling period. Seeds germinate in a single flush, at temperatures as low as 41°F. A smaller percentage of seeds can germinate during the summer and autumn at temperatures of 68°-77°F. Seedlings emerge from the top inch of soil. Some seeds can geminate in darkness, but the germination percentage is higher under light conditions. Flowering occurs from June to November. A single plant may produce from 125-200 to 6400 achenes, which can be dispersed by birds and animals after ingestion. Seed dispersal may also occur via rain, streams, irrigation systems, and other water courses.

Management Approaches

Mechanical methods used for the control of prostrate knotweed are usually not efficient alone. They are more effective in combination with chemical treatments.

Biological Control

Several insect species have been suggested as a potential biocontrol agent for this weed, though none are currently available.

Mechanical and Cultural Control

Knotweed flourishes in compacted soils with low oxygen diffusion. Soil conditions can be made less favorable using soil aeration techniques. If possible, future compaction should be avoided.

Chemical Control

The best control results will be obtained in the spring when plants are still upright and actively growing, from seedling to flower stage. Pre-emergence herbicides can be effective if applied in late fall/winter. Post-emergence herbicides are mostly ineffective on larger plants. While there have been no reports of herbicide resistance in prostrate knotweed in the United States, there have been two reports of resistance in Western Europe. For more information on resistance in Europe please see http://www.weedscience.org/Summary/USpeciesCountry.asp?lstWeedID=131&FmSpecies=Go

Examples of herbicides that can be used to manage prostrate knotweed

Consult herbicide labels for additional rate, application, and safety information. Additional herbicide information can be found at http://www.greenbook.net.

Herbicide Active Ingredient trade name	Mode of Action	Product per Acre	Application Time or Growth Stage
Alfalfa
Pronamide	Group 3 (Microtubule assembly inhibition)
*Kerb 50-W		1 - 4 pounds/A	Recommended for fall or winter applications to alfalfa for pre-emergence control of prostrate knotweed. Check label for specific instructions based on state.
Grass Grown for Seed
Dicamba	Group 4 (synthetic auxins)
*Clarity		8 - 24 ounces/A	Apply 8 - 16 fluid ounces per treated acre on seedling grass after the crop reaches the 3 - 5 leaf stage. Apply up to 64 fluid ounces of on well-established perennial grass. For best performance, apply when weeds are in the 2 - 4 leaf stage and rosettes are less than 2” in diameter.
Wheat, Except Durum and Wampum Varieties of Spring Wheat, and Barley
Metasulfuron; Thifensulfuron; tribenuron	Group 2 (Inhibition of acetolacetate synthase ALS)
*Ally Extra		0.2 - 0.4 ounce/A	For best results, apply when weeds are actively growing, are no larger than 2" tall, and when crop canopy will allow thorough coverage. Apply when crop is in the 2-leaf stage, but before the flag leaf is visible.
Durum and Wampum Varieties of Spring Wheat
Metasulfuron; Thifensulfuron; tribenuron	Group 2 (Inhibition of acetolacetate synthase ALS)
*Ally Extra		0.2 - 0.4 ounce/A	For best results, apply when weeds are actively growing, are no larger than 2" tall, and when crop canopy will allow thorough coverage. Make applications after the crop is tillering but before boot. Applications should be made in combination with 2,4-D.

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality. Updated Oct 2008

References

For more information and images please visit IPM Bugwood. http://www.ipmimages.org/search/action.cfm?q=prostrate%20knotweed