Primarily in Latvia the Hogweed was introduced as a cultivated plant. Great
expectancy was put on it as a cultivated fodder and a nectar plant.
Nowadays, the distribution of the Hogweed is out of human control and the
species has spread almost all over Latvia, mainly in unmanaged land areas
and near ditches.
In The National Programme of Biodiversity it was
acknowledged that the Hogweed Heracleum sosnowskyi is a very
expansive species that can invade and maintain not only in weedy places and
on road margins but also in natural plant communities. It means that when
starting to the growth of this plant for fodder, the most elementary
precaution principles were not followed.
The Hogweed is very dangerous for humans and causes skin and mucous
membrane burns and is particularly dangerous for children. To extinguish the
Hogweed that has been growing for a longer time is almost impossible.
Therefore, individual attempts have not given considerable results. The
present results testify that to extinguish the Hogweed (not only to limit)
all the possible complex of agricultural, technical and biological methods
must be applied.
Recognising the seriousness of the established situation, Ministry of
Agriculture of the Latvian Republic has provided financial support to
elaborate Provisional Recommendations to localise the Hogweed in
Latvia (only in Latvian).
Characteristics of the Hogweed species
Heracleum sibiricum L. is a native species Latvian flora, in English -
Sibirian Hogweed. It is common all over the country on road margins,
meadows, forests and as a weed in fields.
Heracleum sibiricum is a
morphologically variable species.
Later in Latvia have arrived the other species H. persicum Desf.
ex Fischer, H. pubescens (Hoffm.) Marsch. - Bieb., H. villosum - and
H. mantegazzianum Sommier et Levier - Giant Hogweed that is a
decorative plant. There are also many hybrids between the Hogweeds.
According to the herbarium data of the Institute of Biology, University of
Latvia, investigations and literature data, its possible to conclude that in
the Baltic region in natural habitats two well distinguished taxa have
spread - more common H. sosnowskyi, much more rare is H.
mantegazzianum. Further research is needed to make the final
conclusions. More rare in Latvia is the Giant Hogweed - H.
mantegazzianum Sommier et Levier. This species of the Hogweed grows in
Riga in the Bastejkalns park area. The origin of Giant Hogweed is in the
Caucasus region. Already in the thirties of the last century it was
introduced in Latvia as a decorative plant. Although there have not been
more detailed observations, the botanists consider that in natural habitats
this species occur rarely. The Sibirian Hogweed and the Giant Hogweed can be
separated due to the different leaves.
Heracleum sosnowskyi Manden.appeared in Latvia in at the
middle of the previous century as a cultivated plant and its origin is in
the Caucasus region. Several botanists consider Heracleum sosnowskyi
only as a subtaxa of H. mantegazzianum or H. pubescens.
Therefore, Heracleum sosnowskyi does not appear in the lists of weedy
flora of many West-European countries. For the first time Heracleum
sosnowskyi as a species was described by I. Mandenova in 1944. More
detailed studies were carried out by I. Saciperova. In Latvia Heracleum
sosnowskyi was introduced in 1948 and has found a favourable environment for
its distribution and nowadays actively spreads in the natural habitats
becoming an unwanted and aggressive weed. At the same time it is also
dangerous for the human health.
Photo: Normunds Rustanovics
There is a contradictory opinion about the life span of this species in
Latvia. One view is that it is a biennial plant - in the first year it forms
a large rosette and strong root system, on the second - great size and
inflorescence with a considerable number of seeds. After fruiting the plant
dies. Hogweed is a perennial plant. One of the supposed reasons of
Heracleum sosnowskyi being a perennial plant is based on the
different rate of seed germination in the period post- mature. It can last
between 2 - 4 years. The second reason for being perennial can be that in
the situation of mutual concurrence between the Hogweeds part of the plants
are not able to produce inflorescence 2 - 5 years one after another.
Therefore, the seed production and life span lasts between 3 - 6 years,
sometimes even longer.
Investigations in which the seeds were not allowed to mature due to mowing
before the inflorescence was formed were carried out. The results showed on
the second and the following years the species was able to pass the winter
and produce seeds on the next year and then die after flowering. Many
practical workers consider that even when the mother plant dies, the
off-root buds are able to produce shoots giving rise to new plants and in
such a way being perennial plants.
The new shoots Heracleum sosnowskyi are rather cold resistant and
can bear 4 -7 degrees below zero. It is found out that starting from the
second year in a snow less situation they can survive up to 25 degrees below
zero and below the snow even up to 45 degrees below zero. Heracleum
sosnowskyi is a light demanding plant and at the beginning of their
growth do not bare shade. When the Hogweeds have taken roots then with their
giant shape, fast growth and green mass they oppress the other plant species
and form their own community.
Distribution in Latvia
Heracleum sosnowskyi was introduced in Latvia between 1950-1960. At
the end of the 80-ties and beginning of 90-ties, its distribution in Latvia
went out of human control. The Hogweed rapidly invaded not only in the open
areas but also spaces along water-basins, roads and forests. Nowadays the
distribution of the Hogweed is out of control and it has spread almost all
over Latvia, mainly in unmanaged land areas and near ditches. Its
distribution is favoured due to abandoned land, where earlier land
management activities took place.
Already in 1986 plant protection specialist and botanist A. Rasiņs called
it as a botanical "racoon" and considered it as especially dangerous
quarantine weed.
Most of the specialists also now admit that the Hogweed is a dangerous
plant whose growth is difficult to extinguish. The Hogweeds in Latvia is not
a nature catastrophe, but a disturbing phenomenon that must be limited. A
conclusion can be driven that the Hogweed becoming wild has become a weed
difficult to limit.
Distribution of
Heracleum sosnowsky in Latvia, 2005 (according to
data from Institute of Biology, University of Latvia)
Activities
The analysis of the Hogweed distribution areas testify that the weed is
most widespread in areas where 50 years ago there was an attempt to
introduce as a perspective fodder plant. In open areas the struggle with the
Hogweed is more an economic and agriculture managerial problem, rather than
a technological one. More complicated is the elimination of its distribution
at the watersides of water-basins, near ditches, on road edges, where the
use of herbicides is restricted or not allowed. The variety of land
ownership types in the Hogweed distribution areas witnesses that the
elimination of the Hogweed in Latvia is not anymore only a problem of
farmers and Ministry of Agriculture. To limit the distribution of the
Hogweed co-ordinated activities of Ministry of Nature Conservation and
Regional Planning and the Ministry of Traffic and Municipialities is
needed.
Distribution of the Hogweed is favoured by production of many seeds that
are distributed by wind, water, birds, etc. It is also thanks to the fact
that the Hogweed germinates very fast, it exceeds in growths any other plant
shading it and forcing out of the habitat. In the places where still 2 years
ago wild plants were typical, nowadays only a 3 - 4 m long Hogweed growth
occurs. This process is incredibly fast.
There is a conclusion of experts (scientists and practical workers) that
the minimum increase of the weed in a year is ~ 10 % and the future
prognosis for 2007 could cover 18271 ha land area.
Publications
- Latvāņi. // Lauksaimniecības enciklopēdija. Liesma, R., 1966.
- Rasiņs A., Fatare I. 1986. Sosnovska latvānis - Heracleum
sosnowskyi Manden. - bīstama nezāle Latvijas florā. - Grām.:
Retie augi un dzīvnieki. - Rīga, 8. - 10.lpp.
- Enciklopēdija "Latvija un latviesi" Latvijas daba Nr. 3., 1995, Rīga,
89. - 90. lpp.
- Flora of the Baltic countries 2., 1996, Eesti Loodusfoto AS Tartu,
230p.
- Latvijas PSR flora. 1957., 3., LVI, Rīga, 416.-417. lpp.
- Latvāņi, to izplatības ierobežosana // Pagaidu rekomendācijas. -
Ozolnieki, LLKC, LLU, 2002.- 17 lpp.
Prepared by: M.agr. D.Obolevica
Latvia University of Agriculture
Hogweed and its distribution in Latvia