Scentless chamomile is pretty as a daisy, but the fast spreading weed can reduce crop yields by up to 80 percent.
That’s why the co-ordinator of Saskatchewan’s Noxious Weed Program, Garry Bowes, is pleased about the success of a home-grown program to multiply the scentless chamomile seed weevil, the weed’s arch enemy.
About 2,000 weevils were collected last fall, fed for 17 days and put in a cooler at Saskatchewan Agriculture’s Crop Protection Lab. This spring, 11 to 13 shipments of 60 over-wintered weevils each will arrive at their new home on scentless chamomile patches across the province.
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Adult seed weevils naturally spend the winter in the soil. The adults emerge in spring to feed on scentless chamomile and to lay eggs into its flower buds. The eggs hatch in the bud, producing larvae that eat the florets. Later, the larvae eat young seeds. In August, the adults feed on the leaves and return to the soil for the winter.
“Although they complete their life cycle by feeding on the leaves of the scentless chamomile, and only the scentless chamomile, their damage to the plant is as seed eaters,” said Bowes.
The weevils released in Saskatchewan since 1992 were collected in Germany and Nova Scotia or were overwintered at the Alberta Research Centre in Vegreville, Alta. They were released in the various habitats favoured by scentless chamomile: roadsides, drainage ditches, fence lines, cropland, hayland, pasture, farmyards and wasteland.
Their establishment and over-wintering has been successful in 75 percent of the release sites; the failures were due to spring flooding or, most commonly, human activity such as construction, mowing and herbicide spraying.
Records show that the weevil population increases after introduction. One plant harboured 154 larvae, which destroyed 40 percent of the plant’s seed.
Because of the effectiveness of this biocontrol agent, Saskatchewan’s overwintering program was started to increase the numbers available for release.
Those wishing to release seed weevils on their property may contact their local extension agrologist.
The demand outstrips supply, but names will be added to the waiting list.
“Next year, we hope to have more seed weevils available because we plan to continue the overwintering program.”
Bowes was pleased with the first year’s effort but said it can be improved.
“Meanwhile, we are also continuing an integrated approach using other biocontrol agents: a stem weevil and gall midge, both of which are thought to reduce the vigour of the scentless chamomile. Hopefully, all of them will reduce the presence of scentless chamomile across Saskatchewan,” he said.
