Japanese Knotweed belongs to the family "Polygonaceae” and Genus “Reynoutria”. Polygonaceae is a family of flowering plants which includes herbaceous perennial broadleaf weeds also called Buckwheat in the US. Japanese Knotweed is a non-native invasive herb in the US. It exists from ground zero to 8200 feet elevation. It was brought to the US as an ornamental plant, while some sources report its invasiveness as the result of ship ballast carrying its seeds in New York. With time Japanese knotweed escaped cultivation and became a problem for riparian lands. Japanese Knotweed most often grows in areas having soil pH ranges between 3.8 to 6.2 with less than 120 frost-free days.
The name Japanese Knotweed if self and another common name Fallopia japonica signify that the species originated from Japan including, the parts of China and Korea in East Asia. It has become a pest and an invasive plant species in the majority of the US. It is widely distributed throughout the US than its counterparts except for Arizona, North Dakota, and New Mexico. However, some sources report its presence in Arizona as well. Now, Japanese Knotweed takes many landscapes that got filled with dirt from riparian areas. It's a prominent weed along roadsides, water parks, ravines, and streams, besides its prevalence in garden beds, hedges, and ornamental landscapes.
Japanese knotweed leaves are ovate and arranged alternately and can measure between 3 to 6 inches in length and width, and the leaves' base truncates. It is a rhizomatous, stout, and perennial plant that stores nutrients in the base. Japanese Knotweed may go up to 12 feet tall with hollow and erect stems. Adventitious roots are very fine and threadlike and white in appearance. Rhizomes are usually knotty and dark brown having a diameter up to 3 inches or more. Rhizomes often spread between 25 to 65 feet laterally with a central taproot deep into the soil. The plants remain shrubby and woody near the base and fleshy and hollow from the top. The Flowers are borne on leaf axial and terminal racemes that could measure up to 5 inches long. The seeds have three-winged achenes, and the flower color is creamy-white.
Japanese Knotweed often pollinates throughout the US. However, Butterflies, ants, and beetles also help pollinate them. Japanese Knotweed male and female plants possess vestigial reproductive parts of the opposite sex. Either male or female organ remains functional for performing pollination job. The viability of the seeds decreases with a chosen pollination style but, it's a very complex phenomenon. If a Japanese Knotweed plant produces all viable seeds, the count could rise to 1 million seeds per plant. Seed dispersal is always through wind, water, birds, or insects. However, the germination percentile is low, and none of the North American origin plants produce viable seeds. The success rate of establishing a plant from the seedlings is also rare. The above-ground parts can't survive an extreme cooler climate, while the success rate of rhizome survival keeps them going into next spring.
Eliminating the rhizome system of the plant could help because a creepy underground stem is responsible for new plant growth. It may take two consecutive years to control Japanese Knotweed provided a follow-up herbicide application made after every cutting. Late season cutting and herbicides applications are more favorable since the nutrients manufactured by the above-ground parts are transported for underground storage during this period.
There is no absolute solution for controlling Japanese Knotweed other than using a non-selective herbicide that could kill the established plants of all ages and suppresses the new growth. Compare-n-Save contains Glyphosate 41%, and it remains very effective against Japanese Knotweed provided you follow the label instructions.
Add 2.5 to 3 ounces of Compare-N-Save in one gallon of water to treat 300 square feet area.
Another product chemistry is similar to that of Compare-N-Save with the addition of Imazapyr. Imazapyr is a systemic herbicide and moves throughout the plant tissue to stop the synthesis of growth enzymes. RM43 application can be suggested for only those spots which are bare lands and predicted to remain uncultivated for the next 12 months. The glyphosate ratio is 43.68%, and Imazapyr contributes about 0.78% in this chemistry. Please remember, RM43 is also a non-selective herbicide and kills everything green in 3 to 4 days. However, it may take up to 14 days to clear the resistant or toughest weeds.
there is no need to add any surfactant in the solution as RM already contains a surfactant that dries very quickly. A 32 ounces’ product is sufficient for treating between 4000 to 4500 square feet, or you may add between 6 to 7 ounces per gallon of water for spot treatment.
Ortho WeedClear is an ideal mixture if your climate supports the growth of Japanese Knotweed, and there's fear that it could infest garden plants or turfgrasses. It contains Quinclorac (0.104%), 2,4-D (0.313%), and Dicamba (0.029%,) and these ingredients check the growth of Japanese Knotweed at a very early stage when they have 4 to 5 leaves. The mode of action is both through leaves absorption and roots penetration. The result is quick and visible after 3 to 4 days of application.
Ortho WeedClear is in a ready-to-use formulation. Only connect the product packaging with your garden hose and go for a 5000 square feet area.
The active ingredients of Blindside Sulfentrazone (60%) and Metsulfuran (6%) give brilliant knockdown effect on several broadleaf weeds besides Japanese Knotweed. It's a combination of selective herbicides which stop weeds growth through foliage and roots penetration. This combination is also promising for some cool-season and the majority of warm-season turfgrasses. It’s quick in results, and repeated spray could provide long control.
Add only half of a teaspoon in one gallon of water and target Japanese Knotweed.
Learn How to control and get rid of other weeds in our complete Yard Weeding Guide.
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