Story of the Weeds: Scentless Chamomile
Weed Name and Identification
Common Name: Scentless Chamomile
Scientific Name: Tripleurospermum inodorum (synonym Matricaria perforata)
With its cheerful daisy-like flowers and finely divided, fern-like leaves, scentless chamomile might seem harmless. But in northwest-central Alberta, it’s a sign your pasture or field could be under stress. This weed can grow as an annual, biennial, or short-lived perennial, and it’s prolific; a single large plant can produce up to half a million seeds in one season. Unlike true chamomile, its leaves are nearly odorless when crushed.
What It Indicates About Soil
Scentless chamomile thrives in moist, disturbed soils with low competition. You’ll often find it in low-lying wet spots, around sloughs, ditches, and compacted areas near gateways or watering sites. Its presence can indicate:
Low fertility, especially nitrogen deficiencies
Overgrazing, leading to bare patches
Compacted or poorly drained soils, where other forage plants struggle
When this weed shows up, it’s telling you that the pasture needs attention; healthier, well-fertilized, and rested pasture stands typically outcompete it.
Ecological Role
Scentless chamomile is a pioneer species, quickly invading disturbed or bare soil. Its fibrous roots help stabilize soil temporarily, but large infestations crowd out desirable native plants and productive forages. While it does provide some pollen for bees and flies, its overall ecological impact is negative, reducing biodiversity and pasture productivity.
Livestock Interaction
Palatability: Very low. Cattle, horses, and sheep generally avoid it.
Safety to livestock: Not toxic, but can occasionally cause blistering on muzzles when grazed.
Impact on pasture: Avoided plants lead to selective grazing of desirable forages, which weakens pasture health over time.
Forage value: Essentially no nutritional value; infestations reduce overall forage quality and usability.
Management and Replacement Strategies
Prevention is the best defense. Clean equipment, use weed-free seed, and monitor regularly to catch small patches early.
Soil and pasture management:
Maintain strong, competitive forage stands with proper fertility and rotational grazing.
Avoid overgrazing, and rest pastures to allow grasses to recover and fill in bare spots.
Improve soil fertility, especially nitrogen, to support vigorous grass growth and help suppress weeds.
Address compaction in problem areas (e.g., aeration, reducing heavy traffic, or improving drainage) to promote deeper root systems and healthier forage.
Mechanical control:
Cultivation: Shallow tillage in fall or spring disrupts seedlings and helps reduce the seed bank. Clean equipment after use.
Mowing: Must be done early before flowering and repeated. Plants can produce new flowers below cut height, so mow each time slightly lower than before.
Hand-pull isolated plants before they set seed, especially around sensitive areas.
Chemical control:
Selective broadleaf herbicides (such as those containing 2,4-D or dicamba) can be effective, especially when applied at the seedling or rosette stage.
Always follow local guidelines and consider the impact on nearby legumes.
Biological control:
The seed weevil (Omphalapion hookeri) and gall midge (Rhopalomyia tripleurospermi) reduce seed production by attacking flower heads.
Works best as part of an integrated approach and takes time to establish.
Avoid mowing or spraying in areas where weevils or midges are active.
Replacement forages:
Once scentless chamomile is controlled, reseed with species that are:
Dense-rooted and competitive
Adapted to your local soil type and moisture conditions
Try combinations such as:
Smooth bromegrass, orchardgrass, or meadow brome for vigorous, grazing-tolerant ground cover
Alfalfa and white clover for nitrogen-fixing and high-quality forage
Alsike clover or reed canarygrass in wetter areas to help fill low spots and provide strong moisture tolerance
In cropland rotations, consider barley or winter wheat, which compete strongly with chamomile (avoid flax and lentil on infested land)
These species and strategies help suppress chamomile regrowth, improve soil health, and restore a resilient, productive pasture or field.
Sources and Further Reading
Alberta Agriculture and Forestry – Scentless Chamomile: Biology and Control
Alberta Invasive Species Council – Scentless Chamomile Fact Sheet
Saskatchewan Ministry of Agriculture – Problem Weeds: Scentless Chamomile
Sano Animal - Indicator plants – Decoding the secrets of our pasture’s vegetation
Saskatchewan Ministry of Agriculture — Forage Species Selection Guide
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