JAPANESE HOPSHUMULUS JAPONICUSHEMP FAMILY (CANNABACEAE)Bob DeWittMDC- Private Land Services
BACKGROUNDJapanese hop was originallyimported to America in the late1800s for use as a tonic in Asianmedicine and as an ornamentalvine. It is still sold for thesepurposes today. The common hop(Humulus lupulus) contains bitteracids and essential oils used aspreservative and flavoring inbeer, but the chemistry of Japanesehop is less desirable for thatpurpose.
HABITAT IN THE UNITED STATES• Prefers plentiful sunlight and moisture, rich exposed soil• Commonly found along stream banks and floodplains• Growth is less vigorous in shade and on drier soils, but it can grow in disturbed areas with fairly moist soils, including roadsides, old fields, and forest edges• In milder climates, it can survive the winter
ECOLOGICAL THREAT• Spreads to cover large areas of open ground or low vegetation including understory shrubs and small trees• Vines grow rapidly during the summer, climbing up and over everything in their path• Can form dense mats several feet deep, blocking light to plants underneath• Vines also twine around shrubs and trees causing them to break or fall over• Japanese hop is invasive in riparian and floodplain habitats where it displaces native vegetation, prevents the emergence of new plants, and kills newly planted trees installed for streamside habitat restoration.
IDENTIFICATION• Climbing or trailing growth habit• Leaves are approximately 2 to 4 inches long and are divided most commonly into 5 (range is 3-7) distinct lobes. Leaves are rough to the touch and occur on petioles that may reach 8 inches in length• Stems with rows of fine downward pointed prickles• Look-a-like: Wild cucumber (Echinocystis lobata) • Also has 5-lobed leaves and a similar growth habit • However this weed has tendrils and does not have the downward pointing prickles along the stem
REPRODUCTION• Japanese Hops is dioecious, with female (pistillate) and male (staminate) flowers produced on separate vines.• The flowers are wind-pollinated. Each female flower produces a single seed that is ovoid and flattened. This vine reproduces by reseeding itself. It often forms dense colonies of overlapping vines.• Japanese Hops prefers full to partial sun and moist to dry-mesic conditions. It tolerates almost any kind of soil (sandy, gravelly, loamy, or full of clay), but grows most vigorously in a fertile loam. This vine can spread aggressively by reseeding itself.
BIOLOGY & SPREAD• Seeds germinate in early spring. New plants continue to emerge as the season progresses if sunlight and moisture are available.• Newly germinated seedlings may spend several weeks in the tiny 2-leaf cotyledon stage, but once hot weather arrives, grow very rapidly.• Many thousands of hop plants per acre may be produced, eventually blanketing the land and vegetation.• Flowering occurs early to mid summer with seeds maturing through September. After that, growth slows and the plants begin to decline.• The first hard frost of autumn kills the vines and they quickly disintegrate.• Seeds may be dispersed by animals (including people), machinery and floodwaters.
Manual and Mechanical• Most targeted method, with the least likelihood of damage to other plants• Slow and labor-intensive and best suited for fairly small, readily accessible infested areas.• No extensive or deep root system - is fairly easy to pull or dig when the soil is moist• Hand weeding needs to be started early in the growing season (April – May) while the roots are small and before the vines become tangled with other vegetation. Monthly pulling and monitoring will be needed• Cutting or mowing the hop vines as close to the ground as possible is an acceptable control method - start cutting early (late spring), thoroughly cut entire site and repeat practice frequently until fall dieback• Vines quickly re-grow from the cut stems and from uncut vines around the trees.
Biological• No biological control agents are currently available for release to control Japanese hop. However, the U.S. Forest Service has been investigating natural enemies of plants of Asian origin that are invasive in the U.S. They have identified two moths (Epirrhoe sepergressa and Chytonix segregata) and one fungus (Pseudocercospora humuli), as potential natural enemies of Japanese hops and will continue research on those species. The Japanese beetle (Popillia japonica) has been observed to feed on hop but did not cause extensive damage.
Cultural• Japanese hop prefers direct sunlight and does not tolerate heavy shade. As soon as the tree canopy closes, the hop will cease to be a problem• Practices that favor fast tree growth, early crown closure, and heavy shade will help the new stand survive and outgrow the hop.• Plant fast-growing, tall tree species adapted to the site and that will create dense shade in spring and summer. Space plants close together• Use effective weed control measures. Hop will climb up and over shrubs and small trees, but it needs a ladder of tall weeds• Establishing groundcover vegetation that is thick and growing in early spring could possibly reduce hop germination and seedling survival. Fall plantings of hairy vetch (Vicia villosa), wheat, barley or cereal rye might serve this purpose.
Chemical• Pre-Emergent Herbicide • Because hop seeds are large (about 1/8th in. or 3 mm), it is harder to prevent their successful germination than it is for smaller seeds. Usually combine with post-emergent herbicides later in the season • Apply mid-March; products that possess both pre- and early post- emergent properties may be used through mid-April • If the window of opportunity for pre-emergent application is missed, a combination of a pre-emergent herbicide plus a fairly low rate of a post-emergent herbicide, may be very effective in controlling new growth • Calibration of spray equipment and uniform application of the targeted rate is crucial when using pre-emergent herbicides. • Sulfometuron methyl (Oust® XP at a rate of 1 oz./acre) was found in trials to have the most long-lasting control (through July), with the added benefit of relatively low cost. Metsulfuron methyl, simazine, pendimethalin, and imazapic also provided good pre-emergent control but did not control seeds germinating after June..
• Post-Emergent Herbicide • Two treatments are recommended. Effective combinations include a pre- emergent herbicide in early March, or slightly later if using a product with post-emergent properties, followed by post-emergent application in mid- summer, or two post-emergent treatments (mid and late summer) to prevent the fall seed set. • Applications timed closer to the initiation of seed formation are more likely to prevent seed production before frost. In study plots where post- emergent treatments were applied in June, no newly germinated hop seedlings were observed for the remainder of the growing season. • Of the products tested , metsulfuron methyl (Escort XP® at 1 oz./ac.) and glyphosate (Accord Concentrate® at 1 qt./ac.) provided the greatest control • According to The Nature Conservancy, hop seeds in the soil are unlikely to last more than three years. Repeat treatments for two to three years should be expected especially in areas subject to flooding that may receive influx of seed from upstream infestations.
Vines are covered with hooked hairs which makes working with them painful.Dermatitis and blistering may occur when working with these plants. Use appropriateprotection (heavy pants, long sleeves, gloves, etc.). Bob DeWitt
CASE STUDYDEWITT FARMLamine River BottomCooper County, MO
• Picture shows Spring 2012 – March 24th • Flood of 2011 inundated bottom from May through July • Area was devoid of vegetation until late summer • Mild winter • Early spring warm-up Bob DeWitt
Background• Bottom field was enrolled in CRP through continuous sign-up practice CP-22, Riparian Buffer• Advanced regeneration of typical bottomland species – silver maple, willow, ash, cottonwood with some pecan• Mechanically (post hole auger) planted thin and open areas in field in the spring of 2000 with oak (swamp white, bur and pin ) and pecan• Maintained new planting with multiple annual mowings and herbicide (glyphosate and simazine) through 2005• Left trees on their own beginning in 2005 – Pecans were over 10 feet tall and oaks were 4-6 feet tall, canopy closure was variable, but substantially less than 100%• Didn’t revisit field until summer of 2007 – Japanese Hops had pulled down part of plantation. Trees had been deformed, broken and had died from a lack of sunlight