Davey Tree Flipbooks

20 JAPANESE KNOTWEED (Fallopia japonica var. japonica) PLANT DESCRIPTION Japanese knotweed is a bamboo-like perennial weed with a strong central stem and smaller leaf branches. It is most often noticed in spring to fall in dense, 4–10 foot tall colonies. In early spring pink and green sprouts emerge. Sprouts look similar to asparagus but are much thicker. Japanese knotweed is very distinct and is easily spotted during most of the year in thick colonies. LEAF: Leaves are oval to heart shaped with a tapered point and a smooth leaf margin. The leaves form a dense canopy that assists Japanese knotwood to outcompete most other Ohio plants. STEM: Stems are green to purple and strongly zigzagged. The main stems are hollow, smooth, and chambered. FLOWER: Later in summer, white flower spikes with many small, bell-shaped flowers emerge where leaves meet the stem. Flowers resemble white pipe cleaners at a distance. SEED: Each flower on the spike produces a single seed. Seeds develop as whitish, papery capsules with three wings surrounding a single seed. Seeds turn rust colored or light brown and can persist into winter, which makes Japanese knotweed easy to identify in the dormant season. REPRODUCTION: Seeds contribute to reproduction and can be easily spread by wind or water, but the root system is the primary means of reproduction. The spreading roots help Japanese knotweed form large colonies, thereby displacing all other vegetation. A mature Japanese knotweed plant is capable of producing hundreds of thousands of seeds, most of which drop below parent plants. Some are distributed by wind or water. Mowed cuttings create new colonies as cuttings will develop roots and grow new plants where they are dropped. WHY IT IS NOXIOUS: Japanese knotweed is a rapidly-growing, aggressive plant that can dominate wet areas and ditches. It causes maintenance and safety concerns, but also poses an ecological threat as it displaces more desirable Ohio vegetation. SEASONAL IDENTIFICATION WHEN TO FIND: Japanese knotweed matures by early summer and flowers in late summer. It is easy to identify during all seasons, especially in large unmowed patches. SPRING IDENTIFICATION = EASY TO MODERATE Remnant patches of previous year's growth should still be visible in large colonies if they have not been mowed or laid over by heavy snow. New growth emerges as green and pink asparagus-like sprouts. Hollow stems develop and grow taller and leaves develop to full expansion. SUMMER IDENTIFICATION = EASY Mature plants have lush, oval to heart-shaped leaves, hollow, bamboo-like stems, and soft delicate white flowers that look similar to pipe cleaners at a distance. FALL IDENTIFICATION = EASY Seeds turn rust colored in fall. Some plants drop all seeds, while others remain on the stalks. WINTER IDENTIFICATION = MODERATE Purplish to dark brown bamboo-like canes persist and often hold large amounts of rust- colored seeds into winter. Large colonies are easily visible at a distance. SIMILAR-LOOKING SPECIES GIANT KNOTWEED (Fallopia sachalinense) looks very similar to Japanese knotweed and often grows in the same areas. The leaves are larger than Japanese knotweed and are more spade shaped. BAMBOO (Phyllostachys spp.) is an aggressive ornamental garden plant that can resemble Japanese knotweed's hollow, segmented stems. Bamboo stems are green and woody. The leaves are slender and pointed. LOW HIGH ohio distribution roadside distribution growth seeds ability to dominate difficulty of control WHERE TO FIND: Japanese knotweed is common in Ohio, especially in the eastern half of the state. Japanese knotweed prefers wet sites near rivers and in ditches. It tolerates shade very well, but can also grow in full sun. This plant is easy to find in large patches, dominating all other vegetation. CONTROL METHODS: MECHANICAL: Mow from spring to late summer only if necessary to maintain visibility, weaken perennial patches, and reduce seed production. Expect rapid regrowth. Be careful not to transport cut plant parts off site as new colonies will form where cuttings are dropped and take root. CHEMICAL: Make directed applications to Japanese knotweed with non-selective or selective residual herbicide after full leaf expansion in late spring to flower production in late summer. CULTURAL: Improve drainage and increase sunlight to decrease desirable habitat. RECOMMENDATION SUMMARY: Japanese knotweed is a fast-growing, aggressive perennial that is difficult to control. Accomplishing complete control may take several seasons, so be persistent. For best control, make herbicide applications from late spring after leaves fully expand to late summer flowering. Allow at least four weeks for herbicide to work into the roots before cutting. Plan herbicide applications for consecutive years until control is achieved. Mow to maintain visibility or to weaken the root system's ability to store energy late in the season. Be careful not to transport cut stems to new locations after mowing. Cut plant parts of Japanese knotweed can grow into new plants and eventually large colonies. Improve drainage and increase sunlight to diminish habitat for Japanese knotweed and allow competition from a wider array of Ohio vegetation. Failure to control Japanese knotweed will result in the expansion of patches through spreading roots and development of seeds that can spread the plant to new areas. Japanese knotweed is a major concern for maintenance and visibility beyond the road edge. perennial RIVM LEVEL OF CONCERN

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