It’s a nasty weed cursed at with many names — wild daisy, scentless mayweed, false chamomile, Kandahar daisy and barnyard daisy. Scentless chamomile is an invasive weed that has a hard time decided whether it’s a summer annual, winter annual or even a short-lived perennial. The pesky weed has become a more significant weed in recent years because of its adaptive and invasive nature.
Scentless chamomile is native to northern and central Europe and is thought to have been introduced to Canada either as an ornamental or as a grain contaminant as early as 1910. Generally, you will see this daisy-like flower waving to you from moist, disturbed areas such as ditches, your farm yard, sloughs, shelterbelts and, of course, from your crops. It is a difficult weed to control because of its natural tolerance to herbicides, and tends to be more problematic in the black and grey wooded soil areas of the Prairies due to more consistent rainfall and soil moisture.
Despite the significant yield loss that this weed threatens, there has been limited research into potential control or management options. In the 1980s, extensive research into the distribution, biology and management was conducted by a team of scientist including Bowes, Douglas, Peschken, Thomas, and Woo, then with Agriculture Canada at Regina as well as McClay at the Alberta Environment Centre. Since then, public research has primarily focused on non-traditional control and management strategies. “In recent years, there has been a global movement, particularly in Canada, to reduce chemical herbicide application on crops,” says Russell Hynes, research scientist with Agriculture and Agri-Food Canada (AAFC). “These factors are the main drivers behind recent research to develop biological herbicides, fungicides and insecticides.”
Biopesticides are broadly defined as living organisms or natural products derived from these organisms that suppress pest populations. More widely used in fruit and vegetable crops, fungi, bacteria or viruses are generally the active ingredient in these biopesticides.
In a research project ended two years ago, AAFC scientists explored naturally occurring microorganisms
Scentless chamomile can germinate in the fall, spring or summer
for control of scentless chamomile. In this research, over 700 microbial isolates were evaluated and the fungus,Colletotrichum truncatum was found effective under greenhouse conditions but once applied on older plants, or under field conditions, the efficacy decreased. This fungus is host specific, and different from the one that causes anthracnose on lentil crops (although bears the same species name). Gary Peng, an AAFC research scientist who worked on the project, says, “The focus of our research was to develop a microbial option for biological control of scentless chamomile and an effective formulation to deliver it in a practical fashion. Our findings indicated that the microbial alone was insufficient, but it could be tank-mixed with a herbicide (many registered in-crop herbicides are only effective at an early stage of the weed) for synergy and improved efficacy and consistency.”
Several combinations of the fungus tank mixed with compatible herbicides resulted in a synergistic advantage to increase weed mortality. Primarily, it was Group 4 chemistries such as Lontrel, 2,4-D and MCPA that demonstrated the synergistic effect, but one Group 5 product, Sencor, appeared to be most synergistic. Sencor is registered for control of scentless chamomile but only as a minor use in carrots in eastern Canada.
According to Brian Wintonyk, western agronomy leader with Dow AgroSciences, products like Pre-pass (glyphosate and florasulam) and Spectrum (florasulam, clopyralid and MCPA) show significant control results on scentless chamomile. “In our internal testing, with Pre-Pass, we consistently average 98 per cent control,” he says. “Compared to your standard one litre rate of glyphosate at 92 per cent.” Dow also produces a chemical called Prestige, which is registered for scentless chamomile control, and the previously mentioned Spectrum has the same registration pending. In permanent grass Restore (aminopyralid plus 2,4-D) is registered. Similarly, DuPont is working to add scentless chamomile to the Precision Pac 23-23-5 mix.
But bioherbicides are not the only biopesticide that have the potential to benefit farmers looking for new scentless chamomile control options. Insects are also utilized as biological control agents for scentless chamomile. By exposing a weed to one or more of its natural enemies to feed upon it, we can limit its growth and reproduction.
According to the Saskatchewan Ministry of Agriculture, plant-eating insects can be used as classical biological control agents, and most of the work to date on the biological control of weeds on the Prairies involves their use. Clark Brenzil, provincial specialist in weed control for the Saskatchewan Ministry of Agriculture, says three insects introduced to Western Canada as biological control agents are the scentless chamomile seed head weevil, the scentless chamomile gall midge and the scentless chamomile stem mining weevil. Saskatchewan Ministry of Agriculture and Saskatchewan Association of Rural Municipalities jointly run the Invasive Alien Plant program to assist rural municipalities to release available biocontrol agents in their areas.
The scentless chamomile seed head weevil does not directly impact the plant or its mortality, but rather lays eggs in the flowers before they produce petals and these larva generally eat up to 11 seeds each. “This insect sees only one generation per year, but can spread out from where it was introduced at a rate of one mile per year.” says Brenzil. “We have been getting pretty good numbers occurring in heads, particularly when things turn from relatively moist to relatively dry and the chamomile population naturally contracts, so there is more competition for fewer flowers,” says Brenzil of the insect’s effect on the weed. The reverse happens when wet conditions return and the weed outpaces the insects. “There is always a lag time between plant response and insect response with classical biocontrol.”
Conversely, the scentless chamomile gall midge does directly affect the plant itself, by reducing plant vigour, something farmers like to see. The gall midge lays eggs in growing points (primary buds, axial buds, flower buds, etc.) and the larva then burrow into tissue. As a result, the plant compensates buy creating a gall around the irritation point, preventing the growth of that tissue while the midge is present. Adults emerge from the galls and must mate and lay eggs again within 24 to 48 hours before they die. Gall midges can have up to three generations per year and as a result spread faster than the seed head weevil.
Lastly, Brenzil comments on the scentless chamomile stem mining weevil. This weevil affects the scentless chamomile by feeding on the pithy centre of the stem. “This insect has not been successful to date,” Brenzil notes. “There are a couple of theories as to why. Since this weevil overwinters in the stem, it could be that our winters are too cold. It was also thought that it might be dispersing too quickly from the release site and therefore have problems finding mates to maintain high populations. If this is the case we might see a resurgence of this insect sometime in the future as populations build up.”
While there is no silver bullet yet for growers looking for management or control options against scentless chamomile, knowing that scientists and chemical companies alike are still exploring options gives us something to look forward to in the marketplace in the future.
MeganOleksynwasraisedonamixedfarmin northernSaskatchewanandwritesfromPigeon Lake,Alta.Aprecisionagriculturerepbyday,she alsorunssouthpawcommunications,acommunications consulting,publicrelationsandfreelance writingbusiness