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L00484 Novak et al. 2010 .pdf


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21st COLUMA Conference

International Meeting on Weed Control
8th - 9th December 2010

JAPANESE KNOTWEED (FALLOPIA JAPONICA (HOUTT.) RONSE DECR.) - COLONIZATION IN CROATIA
Nenad Novak, Veljko Lodeta, Maja Kravarščan

Croatian Centre for Agriculture, Food and Rural Affairs - Institute for Plant Protection, Svetošimunska 25/V, 10040 Zagreb, Croatia
nenad.novak@hcphs.hr; veljko.lodeta@hcphs.hr; maja.kravarscan@hcphs.hr

Summary

INTRODUCTION

Japanese knotweed (Fallopia japonica (Houtt.) Ronse Decr.) is herbaceous perennial plant
native to Asia. It was introduced in Europe in 19th century as an ornamental species. Nowadays, it is present on many lists of invasive alien plants in Europe. First recorded occurrence
of Japanese knotweed in Croatia was on 1970. in Zagreb. Forty years later it has become a
serious threat to many autochthon plants and biodiversity. On many locations in continental
region, it kills native vegetation and forms dense monocultures. Its habitats are very diverse
but usually connected with human activity. It is usually found near traffic roads, in towns, near
water courses, building sites, industrial yards and other urban areas.

Japanese knotweed (Fallopia japonica Ronse Decr., Reynoutria japonica Houtt., Polygonum cuspidatum Siebold & Zucc., Polygonum reynoutria
Makino; family Polygonaceae, order Caryophyllales) is herbaceous perennial plant native to Japan, China, Taiwan and the Korean peninsula. It has
been introduced in Europe (probably in 1849.) as an ornamental species. It was popular exotic plant and in early 1900s the number of reports of
naturalizations increased rapidly (UK, Czech Republic…). These establishments were most likely to have been escapes from gardens. Nowadays,
Japanese knotweed is widely considered an invasive species. It is listed by IUCN (International Union for Conservation of Nature) and ISSG (Invasive Species Specialist Group) as one of the world’s 100 worst invasive species. It is also present on EPPO List of invasive alien plants and many
national lists in Europe. Reynoutria japonica Houtt. and Reynoutria sachalinensis (F.S.Petrop.) Nakai in T. Mori are listed on Preliminary check-list
of invasive alien plant species (IAS) in Croatia. According to our observations Reynoutria japonica Houtt. is present in whole country but especially
aggressive in continental part. Reynoutria sachalinensis (F.S.Petrop.) Nakai in T. Mori is present only locally.

DESCRIPTION AND
PROPERTIES

Picture 1. Red to purple shoots of Japanese knotweed (Recorded by N.Novak)

Red to purple shoots appear early in spring (Picture 1.) but as they
grow, the leaves develop and the plant turns green. Stems arise
from strong rhizomes to form a dense thicket. Leaf size is usually
about 15 cm long by 8 -10 cm wide, broadly oval to partly triangular and pointed at the tip. Flowering occurs in late summer/autumn
and consists of creamy white flowers (Picture 2.). Seeds are about
2.5 mm long, and are triangular and shiny. The rhizome may extend
as deep as 3 m and up to 7 m away from the parent plant laterally. Japanese knotweed can rapidly grow to over 3 (5) m in height
(Pictures 3. and 4.).

Picture 2. Flowering in late summer, Garešnica, Croatia, 4th of September 2009.
(Rec. by N.Novak)

Picture 3. and Picture 4. Very high plants, Botovo and Delnice, Croatia (Rec. by N.Novak & M.Kravarščan)

COLONIZATION AND
ECOLOGICAL IMPACT
Japanese knotweed is distributed in most of European countries, Asia (China, Japan, Korea DPR, Korea Republic),
North America (most countries) and Oceania (Australia and New Zealand). First recorded occurrence in Croatia was
on 1970. in Zagreb. Few decades later it has become a serious threat to many autochthon plants and biodiversity. On
many locations in continental region, it forms dense monocultures and kills native vegetation (Pictures 5.-8.).
Fallopia’s habitats are very diverse. It is usually found near traffic roads (Pictures 9. and 10.), in towns (Pictures 11. and
12.) and other urban areas, watercourses (Pictures 13.-16.), building sites (Picture 17.) and industrial yards. It is found
primarily in open sites, its growth and abundance are depressed in shady sites. It is consequently unable to invade forests and stay on the edge of it. It can hardly be found in stable ecosystems and untouched environment. It is obvious
that human impact is very important factor of its colonization.

Picture 9. and Picture 10. Japanese knotweed next to the traffic roads (Rec. by N.Novak)

Pictures 5.-8. Japanese knotweed reduces species diversity and damages wildlife habitat (Rec. by N.Novak)
Picture 11. and Picture 12. Hunderds of m2 of monoculture of Japanese knotweed in towns - Zagreb and Gospić (Rec. by N.Novak)

Pictures 13.-16. Japanese knotweed near watercourses (Rec. by N.Novak)

CONTROL MEASURES
Big problem in control all invasive species is lack of communication
among experts (agronomist, botanists, foresters…), “legislation people” and public. This is common problem in many countries in whole
EPPO region. Good communication is basic requirement for preventing damages of invasive species.

Picture 18. and Picture 19. Invasive alien species planted and cultivate as decoration (Rec. by N.Novak)

People are not aware of the dangers and damages that invasive
species can cause. It is not unusual to see some invasive alien
species as decorations in gardens (Pictures 4., 18. and 19.). Some of
them can be bought in plant nurseries and that is tipical proof of lack of
communication and big problem in control of invasive alien species.
In Croatia there is no legislation about control and prevention of spreading of Japanese knotweed and other invasive alien species (except
Ambrosia artemisifolia L.). Control measures are provided only sporadic and generally are mechanical (Pictures 20. and 21.). Result of
such condition is that Japanese knotweed continues to spread and
suppress autochtone species.
Picture 20. Cutted stems next to the road (Rec. by N.Novak)

Picture 21. Only part of plant was cutted and new sprouts have
emerged after few weeks (Rec. by N.Novak)

Picture 17. Japanese knotweed near building site (Rec. by N.Novak)

CONCLUSIONS
• Japanese knotweed (Fallopia japonica (Houtt.) Ronse Decr.)
successfully colonize many areas of Croatia
• it is present in whole country but especially aggressive
in continental part
• on many locations in continental region, it forms dense
monocultures and kills native vegetation
• Fallopia’s habitats are very diverse but usually connected
with human activity
• human impact is very important factor of its colonization
and spreading
• in some gardens Japanese knotweed is planted
and cultivates as ornamental plant
• it can hardly be found in stable ecosystems
and untouched environment
• in Croatia there is no legislation about control
and prevention of spreading of Japanese knotweed
• people are not aware of the dangers and damages
that invasive species can cause
• big problem in control all invasive species is lack of
communication among experts, “legislation people” and public
• Japanese knotweed continues to spread, suppress
autochtone species and reduce biodiversity


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