July 20, 2012 13:03
Scentless Chamomile – An Invasive Weed of Increasing Concern
Nadia Mori Regional Forage Specialist, Watrous
Saskatchewan Ministry of Agriculture
Scentless chamomile is a noxious weed in Saskatchewan and has become an increasing problem in Dark Brown, Black and Grey soils. Scentless chamomile can act as an annual, biennial or sometimes a perennial, but reproduces by seed only. A large plant can produce as many as a million seeds and seeds become viable as soon as seed heads appear. The plant has seed heads similar to a daisy with white outer rays and a yellow central disk. The leaves are finely dissected and alternate on a highly branched stem which can grow up to one meter tall.
Scentless chamomile is well adapted to heavy clay soils and tolerates both periodic flooding and dry sites. It is a poor competitor but establishes quickly on disturbed sites. It has a dense fibrous root system which spreads rapidly during wet periods. The weed most often occurs in marginal habitats likes roadsides, farmyards, and slough margins but if conditions are right will also establish on crop, pasture, or hay land.
Scentless chamomile has many characteristics which make it a difficult weed to control. Many of the commonly used herbicides will not control this weed and can require expensive alternative herbicide options. The usual timing of weed control applications may not kill all plants as the plant can grow throughout the growing season. The plant is a prolific seed producer and seeds are easily spread by wind, machinery, and flowing water.
As with any weed, prevention is the best control method. Avoid bringing weed infested hay or seed onto your land, clean equipment before moving to a new field, and be aware that about 26% of seeds will go through a cow’s digestive system unharmed. Monitor field regularly for new undesirable plants and hand weed single plants or small plots as soon as they are discovered. Where tillage is an option, early spring and late fall tillage can help exhaust the seed bank. Mowing can prevent seed production but plants will re-bloom below cutting height. Burning infestations that have finished blooming can prevent seed spread. Grazing is usually not a control option as scentless chamomile is generally unpalatable. Several herbicide products are registered for use on perennial forage stands. Please consult the Guide to Crop Protection for specific details on product availability, rates, and restrictions. Note that desirable broadleaf plants such as alfalfa will also be killed by these herbicides. There are two biological control options available in Saskatchewan and include a seed-head feeding weevil and a gall midge. Contact your local Regional Forage Specialist for availability and collection dates.
Remember that healthy pastures in good or excellent condition are best able to compete with weeds such as scentless chamomile.
For more information on this or other topics please call me at the Watrous Ministry of Agriculture office (306) 946-3219, the Agriculture Knowledge Centre at 1-866-457-2377 or visit our website http://www.agriculture.gov.sk.ca/