Ambrosia artemisiifolia L. - in Switzerland: concerted action to prevent further spreading

Abstract

Summary Common ragweed (Ambrosia artemisiifolia L.) was described in Switzerland already in the end of the 19 th century. Ragweed remained hidden until changing conditions triggered its spread. The invasion of this neophyte in Switzerland is still in a stage, where an effective low cost control should be feasible. A survey of the Swiss agricultural research station, Agroscope Changins-Wädenswil (ACW), former RAC Changins, showed for 2005 a clear trend: Beside a few known foci in arable fields, ragweed grows mainly in private garden sites all over the country. Ragweed follows human activities, and it was observed that its seeds are found in bird grain mixtures. Seeds also enter the regions along the French and Italian borders by agricultural machines and excavated material from building sites. The fact that ragweed endangers public health was one reason to follow more carefully its beginning invasion. The spread of ragweed from private house gardens via compost or via professional gardening as pathways to the fields seems to be very easy. Therefore it was necessary to act rapidly to start an effective campaign in 2005. The information on how to eradicate ragweed went to all municipalities in Switzerland and met increasing interest. This year, the aim was to eradicate ragweed in house gardens, to reduce seed production and to make ragweed known to the population. The campaign will continue in 2006.

Full text

1
Revision 2007:
Station fédérale de recherches en production végétale, Agroscope Changins-
Wädenswil (ACW), CH 1260 Nyon 1, Switzerland
Ambrosia artemisiifolia L. – in Switzerland: concerted action to
prevent further spreading
CHRISTIAN BOHREN
Summary
Common ragweed (Ambrosia artemisiifolia L.) was described in Switzerland
already in the end of the 19
th
century. Ragweed remained hidden until changing
conditions triggered its spread. The invasion of this neophyte in Switzerland is
still in a stage, where an effective low cost control should be feasible. A survey of
the Swiss agricultural research station, Agroscope Changins–Wädenswil (ACW),
former RAC Changins, showed for 2005 a clear trend: Beside a few known foci in
arable fields, ragweed grows mainly in private garden sites all over the country.
Ragweed follows human activities, and it was observed that its seeds are found in
bird grain mixtures. Seeds also enter the regions along the French and Italian
borders by agricultural machines and excavated material from building sites.
The fact that ragweed endangers public health was one reason to follow more
carefully its beginning invasion. The spread of ragweed from private house
gardens via compost or via professional gardening as pathways to the fields seems
to be very easy. Therefore it was necessary to act rapidly to start an effective
campaign in 2005. The information on how to eradicate ragweed went to all
municipalities in Switzerland and met increasing interest. This year, the aim was
to eradicate ragweed in house gardens, to reduce seed production and to make
ragweed known to the population. The campaign will continue in 2006.
Keywords : Invasive Plants, Common Ragweed, Ambrosia, neophytes, public
health
Introduction
Common ragweed (Ambrosia artemisiifolia L.) presently causes growing
concerns in Switzerland. Described first in the 1880s and present sporadically in
the country as a neophyte, ragweed begun spreading intensively during the last
decade. Besides being a weed in arable fields, the plant produces pollen with a
high allergenic potential, that can potentially induce severe health problems in the
population. This situation requires a strong control strategy involving not only
farmers but also staff in charge of managing natural areas, road sides, building-
and gravel industries.
Ambrosia artemisiifolia L. – in Switzerland: concerted action to prevent further spreading
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In Europe ragweed has been known since the 1860s, in France as well as in
Germany. Around 1950 ragweed began to spread in the region of Lyon (France).
In the sixties and seventies it became an increasing problem of public health in
France and today around 140 000 people are affected in the region Rhône-Alpes.
12,1 % of the population around Lyon is allergic (ARVALIS, 2005). In Hungary 90
% of the land area is infested, whereas in former Yugoslavia ragweed is widely
distributed mostly on fallow land as a consequence of war. The Po Valley in
northern Italy is nearly completely colonized (AFEDA, 2005)
This paper presents briefly the historical and current distribution of ragweed in
Switzerland, some information about the presence of pollen in the air with related
medical aspects and, finally, the latest information about the control campaign in
Switzerland.
Figure 1: Distribution of Ambrosia artemisiifolia L. before 1982 in Switzerland
A neophyte in Switzerland
HEGI (1908) reported sporadic findings of ragweed in Geneva, Basel, Zurich
and Berne in the late 19
th
century on fallow ground, along road banks, and in
gravel pits. JAQUET (1925) described it as a sporadic species, growing in the
region of Fribourg. But ragweed remained hidden. The map set up by the Centre
of the Swiss Floristic Network (CRSF/ZDSF 2004) shows that three foci of
ragweed were found before 1994, and about 85 after 1994. Currently, colonization
of Switzerland by ragweed is described as “at the onset of an invasion”
(CORDILLOT 2004) and therefore the costs to control it may be still low. But the
canton of Ticino, on the southern side of the alps, is already heavily infested.
Ambrosia artemisiifolia L. – in Switzerland: concerted action to prevent further spreading
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In the canton of Geneva and in the neighbouring region of the canton of Vaud,
ragweed is present on agricultural fields, along road banks, and in recreational
areas. Other cases – small foci with high infestation rate – have been reported for
a long time in Basel, Ticino, Geneva and recently in Zurich. Ragweed seeds
reached the Geneva region via agricultural machines such as combine harvesters.
Machines for soil treatment are also routinely exchanged between the French
region of Lyon and the Swiss Bassin Lémanique. Excavated material from
building sites is very often been transported between France and Geneva, likewise
between Italy and the canton of Tessin.
Figure 2: Distribution of Ambrosia artemisiifolia L. in 2002 in Switzerland. ○
= observations before 1994, ● = observations after 1994.
These examples show how ragweed benefits from human activities to spread.
Thus, it is not amazing to find ragweed in many private house gardens, or flower
pots in urban and recreational areas. It is also present along traffic routes, growing
often directly along the asphalt. Heavily infested areas are found in gravel pits
where several hectares can be left untouched for a couple of years. Smaller foci
are also known to be present on building sites.
A few reasons may account for ragweed spreading nowadays at a much faster
rate:
 with globalisation, there is more travel, and transportation of goods is
more intensive; ragweed seeds directly benefit from these to spread
further;
 more environmentally-friendly agricultural practises led to less
intensive crop management, in particular against weeds;
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 global warming may help ragweed to grow and spread at faster rates in
the northern hemisphere;
 imported bird seed mixtures, that are distributed nationwide.
Figure 3: Distribution of Ambrosia artemisiifolia L. registered in 2005 by the
Swiss Agricultural Research Station Agroscope Changins–Wädenswil (ACW).
Einzelpflanzen = single plants.
Pollen counts
Ragweed produces pollen in large quantities from August to September which
is often transported by wind over far distances. The pollen of Ambrosia has a high
potential to provoke hay fever and in some cases asthmatic reactions.
Concentrations between 6 and 10 pollen grains per m
3
air represent a moderate
load and more than 10 pollens per m
3
a high load. By comparison, more than 49
pollen per m
3
air represent a high load for grass pollen, which is the main allergen
for hay fever in Switzerland.
The airborne pollen is collected with a volumetric pollen trap and analysed by
light microscopy. In 1969 R.M. Leuschner initiated the pollen measurement in
Switzerland with the first pollen trap in Basel. Since 1993 MeteoSwiss runs the
national pollen monitoring network with 14 measuring stations. The Ambrosia
pollen counts increased in the region of Geneva in the eighties and nineties. Most
of the pollen is transported by wind from neighbouring regions, as shown by the
correlated increase of pollen in Lyon (CLOT et al. 2002). The highest levels of
Ambrosia pollen in Switzerland are detected in Ticino. In 2004 11 days of high
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load were measured in Lugano and Locarno and in Geneva 9 days, whereas in
Zurich no high concentrations of pollen were detected (CLOT et al. 2005).
Medical aspects
If invasion by Ambrosia is left uncontrolled, increase of allergies could heavily
augment the estimated costs of 260 million Swiss Francs for allergy and asthma
(MÜLLER et al, 2000) Experiences from France and North America show that
around 10 % of the population is sensitive to ambrosia pollen (DRASS 2000). A
quarter of them may develop heavy asthmatic reactions. So far, ragweed allergy
with evidence of sensitisation in Geneva remains low with possibly 4 to 5
potential cases in 2004 (TARAMARCAZ et al. 2005). Only 8 of 18 polled medical
practitioners have encountered 1 or 2 patients allergic to ragweed during the 2004
ragweed pollinisation period.
An estimated 100 million CHF is spent in Switzerland to cover overall costs
for treatment of allergic rhinitis (MÜLLER et al, 2000). But numerous sensitive
persons may not consult a doctor. Two third of the patients in Geneva – a town
hosting numerous international organisations – were sensitised outside of
Switzerland (HAUSER, 2004). In the St.Gall Rhine valley in eastern Switzerland
10.6 % of 15 year old students showed sensitivity to pollen of ragweed (GASSNER
2005), amongst other pollen.
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Photo 2: Common ragweed (A. artemisiifolia L.) forms different types of
flowers, probably as a result of stress.
Seed spread and distribution
French observations clearly show that bird seed mixtures contaminated with
Ambrosia seed are an important pathway (CHAUVEL et al. 2004); up to 2500
grains were found in one kg. Another important source for spread is the feed for
small animals such as rabbits and hamsters. It can contain fertile ambrosia seeds,
which can directly reach the field. Seeds are also found in imported sunflower and
sorghum. In most cases it is technically impossible to separate ragweed grains
because weight and size could be similar to other seeds like sorghum. Grain
importers and feed producers should bear the responsibility and sterilise the grains
used for feed.
Seeds of Ambrosia are not airborne, normally they fall on the ground. Spread
of ragweed is greatly favoured by human activities.
Ragweed has a higher spread potential than most indigenous annual
dicotyledonous weed species and most indigenous grass weeds in Central Europe.
Among neophytes, only South African ragwort (Senecio inaequidens DC.),
Canadian horseweed (Conyza canadensis L.) and Japanese knotweed (Reynoutria
japonica HOUTT.) show higher spread potentials (WEBER et al. 2005).
Ragweed is easily mistaken with mugwort species Artemisia vulgaris L. and
Artemisia verlotiorum LAMOTTE.
Distribution of Ambrosia registered in different periods
The first Swiss distribution map set up by the Swiss Web Flora (Fig. 1) shows
some foci of Ambrosia registered before 1982 in the region of Basel, but in the
rest of the country only a few places were infested.
The map established by the Centre of the Swiss Floristic Network shows a
wider distribution of Ambrosia in Switzerland twenty years later in 2002. Mainly
in the western and southern part of the country large areas are infested with
Ambrosia, whereas smaller foci are reported from the rest of the country.
The map of 2005 is based on the survey of the Swiss Agricultural Research
Station Agroscope Changins–Wädenswil (ACW) . It does not show earlier
observations. Single plant foci were found mostly in house gardens following
announcement by their owners and verified by official experts. The high number
of Ambrosia single plant foci reported 2005 in the canton of Zurich (top centre of
the map, north) is the result of a regional publication of the Swiss house owners
association (HEV) in July. It was the time when Ambrosia was grown high
enough, to be recognised by the eyes of a layperson.
Control in agriculture
Control of ragweed with herbicides is difficult in some crops like sugar beet
and peas, and is nearly impossible in sunflowers as both ragweed and sunflower
belong to the same botanical family.
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Since 2003 ACW has been performing efficacy trials with many herbicides
registered in Switzerland. Table 1 shows the efficacy of the herbicides tested.
Knowledge about mechanical control of ragweed could be very important for road
services, as the use of herbicides along roads is highly restricted. Since 2004, we
have been monitoring mowing trials where we count the seed production of
ragweed after a series of various dates of cutting (BOHREN et al. 2005). Our first
observations show that a cut in the first half of September can stop the seed
production, but cannot prevent the production of pollen. It may be very difficult to
inhibit coevally pollen production and seed production.
Ragweed, germinated in cereals, rests in a small stage until the crop is
harvested; coming to the light, it starts to reproduce. The flowering time is
obviously day length dependant and is similar for all plants: it starts from end of
July. Insufficient mechanical or chemical control allows ragweed to sprout
quickly from the base of the stem.
Table 1: Trial site La Petite Grave: Efficacy of various herbicides 2003 –
2007
Ambrosia artemisiifolia L. – in Switzerland: concerted action to prevent further spreading
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La Petite Grave
application of products in field trials of small plots (4 replications); application time according to label for crop
efficacy in %
X= registered in CH
vegetables and others
product
dosage
active ingredient
efficacy 2003
efficacy 2004
efficacy 2005
efficacy 2006/7
mean (estimated)
faba bean
set aside
peas
cereals
potatoes
corn
beetroot
soya
grassland
sugar beet
Atrazin 2 l/ha Atrazin 500 g/l 100 100 X
Lontrel 1 l/ha Clopyralid 100 g/l 100 100 X X
ecol.
comp.
Banvel 4 S 0.5 l/ha Dicamba 480 g/l 100 100 X X X
Basta 5 l/ha Glufosinate 200 g/l 100
Roundup 3 l/ha Glyphosate 360 g/l 100
Afalon 3 kg/ha Linuron 47.50% 100 100 X X div.
Sencor 1 kg/ha Metribuzin 70% 97 100 100 X tomatoes
Gardo Gold 4 l/ha
Terbuthylazin, S-
Metolachlor
187.5 +
312.5
g/l
100 x
Venzar 2.5 kg/ha Lenacil 80% 99 99 X X leek
Arelon 3 l/ha Isoproturon 500 g/l 96 96 X
Golaprex 4 l/ha
Orbencarb,
Metribuzin
803.4 +
66.9 g/l
96 96 X X X X
carottes/
tulips
Topper 3.5 l/ha Ioxynil 240 g/l 95 95
chicorée
etc
MCPB 4 l/ha MCPB 400 g/l 85 100 95 X X X X berries
Equip 2 l/ha Foramsulfuron 22.5 g/l 94 94 X
Callisto 1.5 l/ha Mesotrion 100 g/l 92 92 X
Tomigan 1 l/ha Fluroxypyr
259 g/l
(~180
g/l
acide)
80 85 X
Basagran 3 l/ha Bentazon 81 40 75 X X X X X X flax
Terano 1 kg/ha
Flufenacet,
Metosulam
70 70 65 75 X
Concert 60 g/ha
Metsulfuron,
Thifensulfuron
75
Lanray 5 l/ha Orbencarb, Linuron 88 40 75 X X X X
Rasantan 1 kg/ha
Bromoxynil, DFF,
Amidosulfuron
65 65 X
Orkan 3 l/ha MCPP, Ioxynil, DFF 65 65 X
Primus 0.15 l/ha Florasulam 40 60 X X
Goltix compact 4 kg/ha Metamitrone 50 60 X X
Equip+ Terano 2l+1kg/ha
Foramsulfuron +
Flufenacet/Metosulam
50+ 55 X
Maister 150 g/ha
Foramsulfuron,
Iodosulfuron
65 38 50 X
Bolero 1 l/ha Imazamox 40 50 X
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Refine extra 40 g/ha
Thifensulfuron,
Tribenuron
35 50 X
Goltix triple 2 kg/ha 2x
Metamitron,
Ethofumesate,
Phenmedipham
15 15 X X
Ally Class 50 g/ha
Metsuflufron,
Carfentrazon
15 15 X
Debut 60 g/ha Triflusulfuron 7 25 15 X X
Lotus 0.25 l/ha Cinidon-ethyl 10 10 X X
Titus 40 g/ha Rimsulfuron 5 0 10 X
Dual-Gold 2 l/ha S-Metolachlor 0 10 X X X
Aurora 40 g/ha Carfentrazon 5 5 X
Tramat flow 2.6 l/ha Ethofumesat 5 5 X X
Bandur 5 l/ha Aclonifen 0 0+ 0 X X X
herbicides applied in
autumn in cereals
Arelon, Herold,
Malibu,Fenikan,
Herbaflex, Lanray,
Banaril, Stomp,
Boxer, Concert
0 0 X
Racer 3 l/ha Flurochloridon 0 0 x
Stomp 4 l/ha Pendimethalin 0 0 0 0 X X X X
Boxer 5 l/ha Prosulfocarb 0 0+ 0 X X
Express 40 g/ha Tribenuron 0 0 X
Trifluralin 3.5 l/ha Trifluralin 0 0 X
all registered a.s. in winter oil seed rape applied in autumn 0 0
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Concerted action
Several factors have to be respected to launch an effective control of ragweed.
On one hand it might not be sufficient for public health to apply control strategies
in agriculture for ragweed as for any other weed, because we do not know
anything about a limit of tolerance which guarantees that the amount of ragweed
pollen will not rise above the high load limit of >10 grains per m
3
air. On the
other hand it might not be sufficient to apply control strategies along roadsides or
in natural reserves to prevent ragweed becoming a weed in agricultural areas.
The danger of ragweed pollen to human health requires a concerted action of
several disciplines:
 In cantons of Ticino, Neuchâtel, and Geneva, “Ambrosia Groups” were
created to discuss control strategies. The initiators of such groups often
belong to agricultural services, meteorology agencies and medical
services. Members of the “Ambrosia Group” in Geneva studied in-
depth the dissemination routes of ragweed seeds. Botanists,
environmentalists, road services, medical and agricultural services take
part. Meanwhile the group in Geneva is officially registered by the
cantonal government. Within this group, the Swiss federal research
station ACW, was appointed to work out control strategies for
agriculture (DELABAYS et al. 2005).
 The Swiss Agency for the Environment, Forests and Landscape has
organised multidisciplinary workshops to learn more about ragweed.
 Cantonal offices have also organised workshops to instruct the
personnel working with road services and environmental agencies.
 In 2005 the Federal Departement for Economic Affairs adapted the
ordinance on animal feedstuff with the restriction that all type of
feedstuff put into circulation must be free from ragweed seeds. 2006 the
Federal Council amended the ordinance on plant protection and
declared A.artemisiifolia subject to official control (BUND, 2006).
 Agricultural advisory services are now forced to control every focus of
contamination in the fields because of the invasive behaviour of
ragweed.
 Meteorologists are well equipped to measure pollen in the air, and they
edit periodically a pollen report (METEOSWISS) for allergic persons
which is also broadcasted by the radio stations.
 Medical services study more about the allergic symptoms intensively in
order to treat future patients properly.
 Road services support the information campaign in 2006 finacially.
Information campaign 2005
Experiences from France and elsewhere show that once ragweed is in the
fields, it can no longer be fully controlled. Consequently we must control ragweed
in this stage of early spread, to stop it infesting our fields.
The question in 2005 was, where and how ragweed is located in Switzerland.
To answer this question, ACW published in spring an article on ragweed in the
house-owners journal (BOHREN, 2005). The possibility was also offered to send
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suspect plants to ACW for determination. We have registered in 2005 mostly
single plant foci in house gardens throughout the country. But we have also
registered the infestation of 6 agricultural plots and 22 public facilities with
several hundreds of plants. A massive infestation was discovered in a gravel pit in
the region of Basel.
The echo of the campaign 2005 with more than 120 new foci detected, showed,
that people are very vigilant. A flyer – edited in three different languages – with a
description of the plant and its danger has been printed and sent to all
municipalities. 130,000 copies were distributed within 2 weeks.
Several institutions do continuously edit data sheets and leaflets on ragweed to
inform their clientele. Individual measures often do not solve the real problem.
Private house gardeners are often good observers, and they decide clearly to
tolerate or not a certain plant species in their garden. People sensitive to hay fever
and other allergies will even control public areas. Readers of the house-owners
journal sending plants to our research stations frequently wrote in their
accompanying letter how happy they are to do something good for their health.
The elimination of many single plant foci may help to reduce the number of
seeds produced and may therefore slow down the spreading of ragweed.
The very successful campaign of 2005 will be continued in 2006, aiming at
maintaining fields in Switzerland free of ragweed as long as possible..
Agricultural institutions must be active with the objective to keep ragweed away
from our fields.
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Ambrosia artemisiifolia L. – in Switzerland: concerted action to prevent further spreading
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christian.bohren@rac.admin.ch
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Photo 3: Common ragweed (A. artemisiifolia L.) growing on a building site
near Geneva, Switzerland
Ambrosia artemisiifolia L. – in Switzerland: concerted action to prevent further spreading
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Photo 1: Common ragweed (A. artemisiifolia L.) grown in an agricultural field
near Geneva, Switzerland.
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WITH REFERENCE TO: Bohren C., Common ragweed (Ambrosia artemisiifolia L.) in
Switzerland: development of a nationwide concerted action,
Aus: Journal of Plant Diseases and Protection - Zeitschrift für
Pflanzenkrankheiten und Pflanzenschutz, Sonderheft XX, in Vorbereitung (2006),
ISSN 1861-4051, Eugen Ulmer KG, Stuttgart
Ambrosia artemisiifolia L. – in Switzerland: concerted action to prevent further spreading
by C
HRISTIAN BOHREN AGROSCOPE ACW, NYON SWITZERLAND, 2007