Chamomile, Scentless

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Pest Information
Common Name: Chamomile, Scentless
Family Name: Asteraceae
Latin Name: Tripleurospermum inodorum (L.) Sch. Bip.
Other Names: Mayweed, Scentless Mayweed, Daisy, Barnyard Daisy, Corn Feverfew, Wild Chamomile, False Chamomile, False Mayweed, Bachelors Button
Provincial Designation: Noxious
Life Cycle: Annual, Perennial, Biennial
Mode of Spread: Seed, Vegetative

Detailed Information
Provincial Situation: Scentless chamomile is more prevalent in the central and northern areas of Alberta but is found in all areas of the province.
Where it Grows (Habitat & Ecology): Scentless chamomile is considered naturalized in North America. It is found in all 10 Canadian provinces with populations being most abundant in the Atlantic and Prairie provinces. The plant has no distinct climate requirements indicating that the plant is very versatile and able to adapt to whatever area it is growing in. Scentless chamomile prefers to grow in temperate climates that satisfy its long day requirement for flowering. It is most commonly found in moist, disturbed areas where there is little competition from other vegetation. It agricultural land, scentless chamomile usually first occurs in the low areas of the field and slough margins. It is found in urban areas, alongside road and drainage ditches, fencelines, waste area, cropland, range and pastureland, hayland, riparian areas and industrial sites.

Scentless chamomile is found in a variety of soil types with wide ranging soil characteristics. Across the Prairie Provinces, scentless chamomile is most commonly found in the Black, Dark Grey and Grey soil zones; areas that receive more rain annually than the Dark Brown and Brown soil zones. Scentless chamomile is also found in the Dark Brown and Brown soil zones and where it is becoming more of a problem as it adapts to different climatic conditions.

How it Spreads (Mode of Spread): Scentless chamomile can produce between 300 000 and one million seeds per plant. A dense stand can produce up to 1.8 million seeds/m2. Scentless chamomile has an indeterminate flowering habit, therefore the plants can flower and form seeds continually from May to October. Seeds are viable as soon as the flower head is formed and may germinate at any time throughout the growing season, provided moisture and temperature conditions are suitable. Germination usually occurs when temperatures are between 3-40oC and when soil moisture is at more than 10 percent of the soil capacity. Seeds can remain viable for ten years or more although most will germinate within two to three years after being shed.

Dispersal
Seeds can be distributed by a variety of methods: water, wind, movement with equipment, contaminant in crop seed and animal feed. Scentless chamomile seeds can float on water thereby being distributed by movement with runoff and moving water. The seeds may also pass through the digestive tract of animals unharmed.

Economic Importance (Beneficial Aspects): Scentless chamomile is a preferred source of nectar and pollen for many species of beneficial predators and parasites such as hoverflies, the tachinid flies and the parasitic Hymenoptera. The plant also contains an antiviral substance that inhibits the growth of polio and herpes virus.
Toxicity and Other Concerns: Reduces yields in grain crops, hayfields, pastures and cultivated crops. Yield losses between 30 and 80% have been observed in fields seeded to spring wheat where scentless chamomile infestation was 25 plants per m2. It is unpalatable to livestock and has very poor nutritional value. It can also serve as an alternate host to insect species that may damage other crops or be vectors for diseases of other crops. In natural areas and pastures, it can displace native species and desirable grasses leading to a loss of biodiversity and carrying capacity of the grassland.
Origin: Scentless chamomile was first reported in Canada in 1876. It was first collected in Alberta in 1933 at Lacombe and Sylvan Lake. It was suspected of being introduced into western Canada as a contaminant in crop seed from Europe or as an escaped garden ornamental. It is native to the Caucasus Mountain region in Europe.
How to Control: Integrated weed management (IWM) considers the overall management of a weed species with the objective of preventing the establishment of the weed from ever occurring, to prevent the spread or to minimize the impact. IWM relies on the combination of a variety of methods such as chemical, biological, mechanical, and cultural controls as well as overall preventative measures. Using IWM creates an opportunity to use herbicides more selectively, which reduces the impact on the environment as well as slow the development of weed resistance to herbicides.

Prevention
Prevention is an important management tool for scentless chamomile because scentless chamomile is very difficult to eradicate once established due to its’ prolific seed production and long-term viability of the seeds in the soil. Methods of preventing establishment of scentless chamomile are to use certified seed, tarp grain trucks and to thoroughly clean equipment that has come in contact with scentless chamomile. Harvest and till infested and non-infested areas separately and try to work in non-infested areas first. Ensure equipment has been thoroughly cleaned before moving to a non-infested area.

Animals that have been grazing a site infested with scentless chamomile should not be allowed to enter a non-infested site for several days to prevent establishment of scentless chamomile. Scentless chamomile seed can remain viable after passing through the digestive tract of cattle so the manure produced should be contained until the seed is no longer viable.

Maintaining a healthy, competitive stand of perennial grasses by preventing overgrazing will also prevent scentless chamomile from establishing. Scentless chamomile is not able to compete with healthy rangeland.

Cultural Control
Hand pulling is a very effective method of control for small patches of scentless chamomile. The entire plant should be pulled and placed into garbage bags and then burned or buried deeply into the ground. This is necessary because the florets can produce viable seed as soon as the white petals appear.

Competition
Research has shown that a healthy stand of grass of a vigorous crop will reduce scentless chamomile populations. Smooth brome or cereal crops compete most effectively with scentless chamomile. For example, the reproductive output of scentless chamomile plants can be reduced by up to 49% when a vigorous growing wheat crop is present.

Fertility
Fertilization to maintain competitive forage stands will limit scentless chamomile growth.

Cultivation
Scentless chamomile can be controlled by tillage in early spring or after a killing frost in the fall. Shallow, frequent tillage will destroy seedlings and encourage germination of seeds. Tillage is most effective when soils are tilled before the plant flowers and during hot, dry weather. The plant may re-establish itself when conditions are moist because the shallow, fibrous root system clings tightly to the soil allowing it to continue absorbing moisture and nutrients. Deep cultivation is not recommended because the seeds can remain viable for a long period of time when buried in the soil. The seeds will germinate slowly over a period of up to 10 years after deep cultivation.

Mowing
Regular mowing can reduce vigour and seed production. Viable seed can be produced as soon as the flower head is formed therefore early and repeated mowing is recommended for control of scentless chamomile. The plants can flower below the mowing height so each successive mowing should be lower than the previous one and prior to formation of the seed in order to be effective.

Grazing
Grazing is not a recommended control method for scentless chamomile as the plant has little nutritive value and is not freely grazed by livestock. Good grazing management will prevent scentless chamomile from establishing. Grazing that maintains a healthy, competitive grass stand will prevent scentless chamomile from establishing and help control established chamomile.

Fire
Burning seed heads can be effective to prevent spread.

Biocontrol
Two insects have been identified as potential bio-control agents for scentless chamomile.

Apion hookeri or seed head weevil, was first released in Alberta in 1992. It finds isolated plants, synchronizes egg development with the appearance of the first flower buds and causes significant reductions in seed weight. It has excellent local dispersal ability.

Shoot, rosette and flower gall-midge [Rhopalomyia tripleurospermi (Skuhrava.)] affects plant height and the number of seed heads formed. In Canada damage to plants on cultivated ground has been modest, but the impact is likely to be greater on scentless chamomile growing in competition with other plants. This biological control agent has been established in Alberta.

Integrated weed management
Effective management of scentless chamomile requires an integrated approach combining prevention, competition and chemical controls. Prevention of seed set and establishment of a competitive stand of desirable plants is an effective integrated weed control strategy for this plant. For example, hand picking a small patch of scentless chamomile followed by treatment with a registered, residual herbicide will allow desirable species to establish that will outcompete scentless chamomile and prevent it from re-establishing itself.



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Last Modified: December 20, 2011

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