Fall tillage can restrain scentless chamomile, but a long-term plan is needed to get it under control, says an agriculture fieldman in Alberta’s Leduc County.
“We’re pretty active in the fight against scentless chamomile,” said Rick Thomas of Nisku.
Last year, county staff handpicked 25,000 pounds of scentless chamomile from roadsides, fields and wasteland in their area just south and east of Edmonton.
Thomas said the county tries to implement a three-year plan for controlling heavy infestations of the daisy-like weed that can take over fields and is a nightmare to eliminate. It can produce millions of seeds and develops a massive root system.
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The county applies herbicide the first year and possibly the second year, depending on severity of the infestation, followed by hand weeding in the third year.
It has built a database to pinpoint scentless chamomile locations and severity of infestations to develop a strategy to limit the weed’s spread.
“It can bloom and set seed so rapidly.”
In Saskatchewan, a government News release
news said a 1995 weed survey showed the frequency of scentless chamomile in farm fields had increased four fold since 1986.
Data isn’t complete on its occurrence in fields and wastelands.
The weed spreads easily, said Allan Macaulay, an Alberta Agriculture forage specialist at Barrhead.
He has worked with a pedigreed seed producer whose field was contaminated through gas well development. They estimate it will be at least 20 years before the oilfield company is given a reclamation certificate certifying the well site is free of the weed.
Another farmer introduced the weed when he seeded 80 acres with a poor-quality white Dutch clover seed.
“People don’t realize how these weeds get started,” Macaulay said.
“It’s very aggressive.”
Cultivation and competition help beat back the weed.
Cultivation helps weaken the root system and makes it more susceptible to winterkill.
“You can certainly reduce it with fall tillage,” Macauley said.
Seedlings are easier to control than plants that have become established, he added.
To effectively control plants with fall tillage, the roots must be exposed and allowed to dry out.
Alec McClay, an Alberta Research Council scientist, said he and his colleagues have had some success introducing two pests: the scentless chamomile seed weevil and the scentless chamomile gall midge.
In one Alberta site, the seed weevil attacked 50 to 60 percent of scentless chamomile heads.
Seed weevils released in 1993 have been found 14 kilometres from their release site and the gall midge, released in 1999, has been found seven km from the release site, McClay said.
He is pleased with their survival and mobility, but realizes their numbers need to increase substantially to become an effective control.
“It’s not going to have a major impact until they build up to really high population levels.”
He estimates it will take five to 10 years for the insects’ infestation levels to increase to a level that will control scentless chamomile.
A few well-placed gall midges can do considerable damage to the plant, he said. The midge is a tiny delicate fly that lives only a few hours. The females lay eggs in the weed’s growing point, leaf axis and flower buds. The larvae hatch and feed in the plant tissue and the gall stunts the plant’s normal growth.
The weevil is small and black and lays eggs into the flower buds. Hatched larvae feed inside, destroying the seed as it develops.
