Scentless Chamomile: Taxonomy, Ecology, and Control

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Fact Sheet-02-85
Scentless Chamomile: Taxonomy, Ecology, and Control
Brad Schultz, Extension Educator, Humboldt County
Jay Davison, Central Area Plant and Soil Specialist
INTRODUCTION
Corn or scentless chamomile (Anthemis
arvensis L.) is an annual flowering plant (forb)
native to much of Europe, parts of Northern Africa,
and Asia. It has become naturalized in North
America, southern Africa, Australia, and New
Zealand. By 1995, it had been found in 37 of the
lower 48 states, including the adjacent states of
California, Oregon, and Idaho. In northern Nevada
it can be found in the Quinn River Valley, near
Orovada, and possibly other locations.
Scentless chamomile has been listed as a
noxious weed in Colorado, and is a very close
relative to mayweed chamomile or dog fennel
(Anthemis cotula L.), also known as stinking
mayweed and dog fennel. Mayweed chamomile is a
serious problem weed in grain and forage crops
throughout the United States, and also may interfere
with crop harvest. Because of many similarities
(size, shape, phenology, etc.) between scentless
chamomile and mayweed chamomile, scentless
chamomile has the potential to become a serious
problem weed in agricultural areas throughout
Nevada. It has no known economic uses and may
adversely affect (taint) milk if consumed by dairy
cattle.
TAXONOMY
Seedling
At the seedling stage, the cotyledons (first
two leaf-like structures) have an elliptical to egg
shape with rounded tips. These leaves are attached
directly to the stem (i.e., they lack a stem or
petiole). The first true leaves are pinnate; that is,
they have leaflets on both sides of the stem.
Adult Plant:
Mature scentless chamomile (Figures 1 and
2) are usually between 6 and 20 inches tall. The
stems are often branched and have sparse hairs. The
leaves are about 1 to 2 inches long. They occur in
an alternate pattern along the branches, have few
hairs, and are divided into many threadlike
segments. They are not linear (line like). The
flowers have white edges, with a central yellow
flower. They are about 0.75 to 1.25 inches in
diameter. Common plants that scentless chamomile
is confused with are tall chamomile (Anthemis
altissima), mayweed chamomile or dog fennel,
dusky dog fennel (Chamaemelum fuscatum), weedy
dog fennel (Chamaemelum mixtum), and
whitebuttoms (Anacylus clavatus).
Figure 1. Mature scentless chamomile plant.
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Figure 2. Scentless chamomile flowers
PLANT GROWTH AND DEVELOPMENT
In both Great Britain and the northeastern
United States, scentless chamomile has two periods
of peak germination: autumn and spring. If moisture
is provided, seed germination is possible throughout
the year. In Nevada, this species appears restricted
to irrigated fields, storage ponds, and irrigation
ditches. Irrigation in many locations is finished by
early to mid September and fields dry rapidly. Fall
germination and overwintering appear to be
uncommon. All plants observed in the Orovada area
begin growth in the spring.
Spring germination largely occurs from
March through May, with rapid plant growth in
June. Flowering may begin in May and continue
into the fall until the first frost. The first frost kills
mature plants.
SPECIES ECOLOGY
Soils and Climate
In Britain scentless chamomile prefers light,
well drained calcareous or sandy soil. Similar type
soils are common in agricultural fields near
Orovada. Soil pH can range from less than 6 to
almost 8. Scentless chamomile has been found
above 3,300 ft in California, and over 6,200 ft in
England. In England, scentless chamomile typically
occurs in areas with less than 35 inches of
precipitation and mean summer temperatures
around 62°F. The average June and July
temperatures in Orovada are 63°F and 71°F,
respectively. These conditions are similar to
irrigated agricultural fields in many valleys of
northern Nevada.
Scentless chamomile is cold tolerant. It has
grown as a winter annual in the northeastern United
States. It may germinate in the fall, over winter in a
rosette form, and continue growth in the spring. Fall
germination appears unlikely in Nevada due to the
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lack of fall precipitation in most years. Also, most
irrigation has ended by fall. Spring germination is
common due to both rainfall and irrigation. Seed
has been known to germinate year-round if moisture
is available and temperatures are not too cold.
Scentless chamomile is more drought tolerant than
the other mayweed species, which suggests it has
potential to spread to subirrigated meadows
throughout Nevada.
Scentless chamomile can grow well in low
nitrogen (14 ppm) and low phosphorus (0.31 ppm)
environments common on sandy soil. It can
compete effectively with barley on low nitrogen
environments.
Seed Production, Dispersal, and Viability
Reproduction of scentless chamomile is
entirely from seed, and seed production can be quite
large. Research has recorded over 300 seed capsules
per plant, although 35 to 70 are more typical.
Average size plants commonly produce 2,000 to
4,000 seeds per plant. There are no physical
adaptations for dispersal. Dispersal over short
distances is primarily from wind. Dispersal over
moderate distances appears related to the movement
in irrigation water through delivery systems, and
possibly attachment to farm equipment or animals.
Seed has been found to survive passage through the
digestive system of pigeons; thus, birds could
transport seed over long distances. Long distance
dispersal occurs when seed is captured in forage and
seed crops during harvest, and transported to
another area for use.
The seed of scentless chamomile can remain
alive for many years. Researchers found 91%
germination in soil-stored seed after 3 years, and
47% germination after 11 years. Seed germination
appears to increase substantially after the seed has
been in the soil for a 4 to 10 month period. Also,
one study found germination increased from 8% to
100% after passage through the digestive tract of
pigeons. Scentless chamomile seed has a tough seed
coat that must be softened before germination can
occur. Soil microorganisms, faunal digestive
systems, and perhaps freeze thaw cycles, remove
the seed coat.
GROWING LOCATIONS
In the Orovada area, dense stands of
scentless chamomile have been found along the

edges of roads and irrigated fields, and along
irrigation ditches and tailwater ponds (Figure 3).
Widely scattered plants have been observed in
alfalfa seed, alfalfa hay, and grain crops. These are
common locations for the plant in Great Britain,
although it often has a high abundance in cereal
crops.
Figure 3. Typical habitat conditions for scentless
chamomile at Orovada. White flowered plants are
scentless chamomile.
CONTROL
Once scentless chamomile has established
and produced seed at least once, eradication is
almost impossible. The seed can live in the soil for
more than 10 years and have about 50% viability.
Given the high seed production per plant, this
results in a large number of live seeds for many
years after treatment begins. Control of the plant is
a more realistic goal than eradication. Several
control methods are possible and can be used in
conjunction with one another.
Numerous herbicides have been tested and
found to effectively control mayweeds, including
scentless chamomile. These include: Roundup Pro,
Telar, Tordon, Transline, Escort, Velpar, and Oracle
(a dicamba product). Other herbicides may also be
effective, but have not been tested specifically on
scentless chamomile or the closely related
mayweeds. Scentless chamomile is resistant to 2,4-
D and other phenoxyacetic acid herbicides. If
repeated herbicide applications are used, the
applicator should alternate between chemicals to
reduce the possibility of developing herbicide
resistance.
Each herbicide known to control scentless
chamomile has very specific instructions on the
product label. Some herbicides cannot be applied to
each of the specific growing conditions in which
scentless chamomile occurs (e.g., along irrigation
ditches). The specific conditions under which each
herbicide should be can be found on the product
label. These labels can be accessed on the internet
(Table 1).
Table 1. Current Internet addresses for herbicide labels for products known to control mayweeds, including
scentless chamomile.
Herbicide Company Web Site Address for Label
Escort DuPont http://www.dupont.com/ag/us/prodinfo/prodsearch/information/H63665.pdf
Oracle
(Dicamba)
Gharda http://www.ghardausa.com/Pdf%20files/oracle_specbk_2001.pdf
Roundup
Pro
Monsanto
http://www.farmsource.com/Labels/RUPProCG.pdf
Telar DuPont http://www.dupont.com/ag/us/prodinfo/prodsearch/information/H63735.pdf
Tordon
22K
Dow
Chemical
http://www.dowagro.com/webapps/lit/litorder.asp?filepath=label/pdfs/noreg/010-
00094.pdf&pdf=true
Transline
Dow
Chemical
http://www.dowagro.com/webapps/lit/litorder.asp?filepath=label/pdfs/noreg/010-
00096.pdf&pdf=true
Velpar DuPont http://www.dupont.com/ag/us/prodinfo/prodsearch/information/H64113.pdf
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Once herbicides reduce the density of large
infestations, removal of remaining plants is feasible
by mowing, hoeing, hand pulling, disking, or other
methods. Scentless chamomile is an annual plant
that reproduces only from seed. Removing the
flowers before seed is set effectively eliminates
future plants. Small infestations can be controlled
easily by mowing or cutting the plants prior to seed
set.
Treated areas that lack desirable,
competitive vegetation are susceptible to
reinfestation. The area should be seeded to and
managed for an acceptable species, to competitively
exclude scentless chamomile and other weeds.
If scentless chamomile occurs on cropland
and has viable seed when machinery is used in the
field, the equipment should be washed afterwards. .
This will reduce the chance of seed being moved
from one area to another.
Biological control has been researched in
Canada but has not been found to control the plant
by itself. The biological agent is a seed-head weevil
(Omphalaplon hookeri). Research has found this
species attacks up to 70% of the seed-heads, but
over 170 seeds/head can still be produced, with
55% viability of the seed.
USDA Agricultural Research Service. 2002.
Germplasm Resources Information Network
(http://www.ars-grin.gov/cgibin/npgs/html/tax_search.pl?Anthemis+arvensis).
National Plant Germplasm System.
BIBLIOGRAPHY
Bowes, G. B. 1999. Scentless Chamomile Control
on Roadsides. The Rural Councillor 34(10):1-4.
Harris, P. and A. McClay. 2001. Omphalapion
hookeri Kirby. Seed-head weevil .
(http://res2.agr.ca/lethbridge/weedbio/agents/amo
phook.htm). Lethbridge Research Centre, Alberta,
Canada. 3 pp.
Kay, Q. O. N. 1971. Bilolgical Flora of the British
Isles. Anthemis arvensis L. Journal of Ecology
59:637-648.
USDA Natural Resources Conservation Service.
2002. Plants Profile. Anthemis arvensis L. Corn
Chamomile The PLANTS database.
(http://plants.usda.gov/cgi_bin/topics.cgi?earl=fac
t_sheet.cgi). National Plant Data Center, Baton
Rouge, LA. 708774
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