Presentation on the invasive Japanese hops.

1. JAPANESE HOPS
HUMULUS JAPONICUS
HEMP FAMILY (CANNABACEAE)
Bob DeWitt
MDC- Private Land Services

2. BACKGROUND
Japanese hop was originally
imported to America in the late
1800s for use as a tonic in Asian
medicine and as an ornamental
vine. It is still sold for these
purposes today. The common hop
(Humulus lupulus) contains bitter
acids and essential oils used as
preservative and flavoring in
beer, but the chemistry of Japanese
hop is less desirable for that
purpose.

3. 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

4. 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.

5. 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

6. 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.

7. 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.

8. CONTROL

9. 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.

10. 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.

11. 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.

12. 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..

13. • 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.

14. Vines are covered with hooked hairs which makes working with them painful.
Dermatitis and blistering may occur when working with these plants. Use appropriate
protection (heavy pants, long sleeves, gloves, etc.).
Bob DeWitt

15. CASE STUDY
DEWITT FARM
Lamine River Bottom
Cooper County, MO

16. • 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

17. 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

18. Bob DeWitt
March 24, 2012

19. Bob DeWitt

20. Bob DeWitt

21. May 12, 2012
March 24, 2012

22. Bob DeWitt

23. Bob DeWitt

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25. Bob DeWitt

26. QUESTIONS?
Acknowledgements:
http://www.nps.gov/plants/alien/
index.htm Plant Conservation
Alliance-Alien Plant Working
Group
http://plants.usda.gov USDA
PLANTS Database