Canada fleabane (Erigeron canadensis) is becoming one of the more common weeds in no-till corn and soybeans. It had previously been kept to background levels by tillage, but has found a new environmental niche in fields with less soil disturbance.

Canada fleabane germinates in the fall and creates a basal rosette with elliptical leaves covered with short hairs. In the spring it grows an erect stems with little branching short stiff hairs. Canada fleabane can be grown past its controllable stage by the time the crop is ready for post sprays.

Resistance issues
Recently this plant (called marestail or horseweed in most areas of the U.S.) was in the news as it is the first broadleaf weed to be found to have developed a resistance to glyphosate. Researchers have confirmed resistance in at least 3 fields in Delaware and suspect additional fields in New Jersey and Maryland. These Canada fleabane plants survived research applications of up to 10X the normal rate of glyphosate in Roundup Ready® soybeans. Fields had been sprayed with both burndown and postemergent glyphosate application for each of the last three years.

Glyphosate resistant fleabane has not been found in Ontario. However, over the past 10 years in Ontario, the use pattern of glyphosate could favor resistance development:

• Ontario no-till soybean growers have found that glyphosate as a burndown herbicide is required in almost all situations.
• Roundup is also used a second time in Roundup Ready® soybean fields.
• Glyphosate is sometimes for also used for preharvest applications.

Be vigilant about watching for irregularly shaped patches or unexplained escapes of Canada fleabane. Remove them before they go to seed, and contact your Dow AgroSciences representative for information on developing control plans reduce the risk of resistance development.

Control options
Corn: Fieldstar*
Soybeans: (including no-till soybeans) Broadstrike* Dual™ Magnum™, No-till Powerplay.


Source:
"Canada Fleabane" Crop-Pest Ontario May 18, 2001


®Roundup Ready is a trademark of Monsanto Company, Monsanto Canada Inc., licensee.
™Dual is a registered trademark of a Sygenta group company.
™Magnum is a trademark of a Sygenta group company.