The Fieldman’s Files – Dealing with weed issues

A portion of the weeds picked by the youth group, ready for incineration. Contributed photos
A portion of the weeds picked by the youth group, ready for incineration. Contributed photos

Normand Boulet
CCA, Ag fieldman
M.D. of Smoky River No. 130

Every year I receive hundreds of phone calls, texts and e-mails looking for information; status of the plant (is this a noxious weed?), but plant identification and how to deal with them are the most common questions.

The methods of dealing with weeds varies significantly depending on what the plant is, how many are present and other issues (is there a crop, what’s the growth stage of the crop, is it under-seeded, are there trees nearby, a water course?

How mature are the weeds; seedling, bolting, ready to set seed?). To give a proper control strategy requires a great deal of information. A couple Scentless chamomile in bloom are best dealt with if pulled from the ground including the root, bagged and incinerated to kill the seeds to prevent them from spreading.

Hand pulling a patch of toadflax with its creeping root system is generally not very effective, it’s a good stop gap measure to prevent seed set but that patch is coming back. In a field scale infestation, is herbicide the best option, or would cutting and silaging the crop to prevent seed set be better?

This summer there are two weed situations that really stand out, both were significant areas of Scentless chamomile, both were discovered in bloom.

One was discovered by a weed inspector, it’s an industrial site which has rough terrain covered in grass, clovers and of course Chamomile. The other was in a canola crop and it was discovered by the farmer while swathing, so obviously late in the season.

It would be best to understand Chamomile a bit before we go on. Scentless chamomile is a member of the sunflower family (like our thistles, daisies and of course sunflowers). The sunflower family is also called the Composite family, the flower head is ‘composed’ of many tiny florets, each of which can produce seed. The tiny Chamomile “flower” is very similar to the massive sunflower “flower”, you have the outer ray florets, the petals which are showy to attract pollinators and the centre made up of fruit bearing florets – which make the seed.

Chamomile has white rays on the outside, hundreds of florets in the yellow centre so each daisy like “flower” is capable of producing hundreds of seeds. The chamomile flower has viable seed as soon as the flower opens, and every day the flower stays open and is visited by pollinators more viable seed is created.

As the flower head fills with seed the yellow centre goes from a flat disc to a brownish bump, the petals droop and fall away (having done their job). That group of flowers is fully “in seed’ and as it dries seeds fall to the ground, infesting the land further. Chamomile is an indeterminate plant which some people call “Mayweed”, it’s very early to get going, often blooming in May.

As an indeterminate plant those first May blooms can be done, dropping seeds to the ground in late May while new blooms are opening on that same plant, right up until freeze up. Chamomile is tough too, it usually won’t “freeze-up” until -10 or less. Chamomile can act as an annual, bi-ennial or perennial, so it adapts to any situation.

In the industrial site we were dealing mostly with perennial plants, adapted to compete with the perennial grasses and clovers. In the second situation its likely most plants were annuals, germinated after the in-crop herbicides had been used and freshly in bloom on August 30. Chamomile only spreads by seed (lots and lots of seed) and the seed can stay viable in the soil for years so it’s really key to prevent seed set as much as possible.

The Weed Control Act of Alberta lists Scentless chamomile as a Noxious weed, landowners are required to control noxious weeds and to control is defined as “to inhibit the growth or spread, or to destroy.” There are municipalities in Alberta which have elevated Chamomile to Prohibited noxious – which requires landowners to destroy the plants, destroy under the Act means “to kill all growing parts, or to render reproductive mechanisms non-viable.”

The industrial situation was “pickable”, the crop situation was too widespread, picking would’ve taken too long. The industrial site owner was contacted and a plan of attack involving picking to prevent seed set was devised, a youth group was employed for a fund-raising initiative and about 3,000 pounds of bagged chamomile was taken off the site to be incinerated by the M.D. of Smoky River No. 130.

Following the picking the area was sprayed with a selective and residual herbicide. Selective to kill the broadleaved plants but to leave the grass to offer competition to any seeds germinating later on, and residual to give a couple more years of control by having herbicide left in the ground so germinating seeds would be killed. So, a youth group got a fundraiser and an education in invasive plant control, and billions of seeds were taken off the site to be destroyed.

For the canola crop, I met with the landowner onsite and we discussed options. Picking would have taken weeks, and each day would have allowed the plants to set seed and possibly increase the number of seeds in the seed bank, so time was of the essence. Most of the field had already been swathed, but the heaviest area of infestation had not. It was decided to go ahead with swathing, and to find someone to bale the infested crop area; wet bales will heat, the expectation was the spoilage would kill any viable seed.

Some composting research indicates chamomile seed was destroyed quickly even when the compost only reached 38.9 degrees, we were hoping for much higher temperatures than that, I was even expecting spontaneous combustion to be possible, canola oil should make for a pretty decent fuel. The producer of the canola crop ended up losing about 25 acres of production and paying for the custom baler to bale and then stack the bales.

The equipment used was cleaned on site to reduce any seed spread. The farmer then bought a “cheap” used combine which he will use only on that quarter section from now on to prevent seed from being transferred from the infested land to his other land with his combine (combines are pretty much impossible to complete clean out, especially of the tiny chamomile seeds).

The landowner and farmer both patrolled the field, picking chamomile plants out of the remaining swaths (where the infestation was lighter, but not non-existent). After harvesting the crop the farmer sprayed the entire field to kill the remaining plants and his intention (and ours) will be to monitor and ensure the Chamomile is not allowed to grow to blooming again.

Controlling weeds requires so much more than, “which herbicide should I use”, and controlling a tenacious plant like Chamomile especially often requires significant effort and cost. Prevention is the best solution, make sure equipment coming onto your land is clean, and any seed or hay purchased does not contain weeds you don’t already have.

For more information, contact me at (780) 837-0043, via email at, or on Twitter (@MDfieldman).

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