Page 183 - PC2019 Program & Proceedings

PLANT CANADA 2019

S151. The use of cereal rye (Secale cereale L.) cover crops to control Canada fleabane (Conyza
canadensis (L.) Cronq.)
*1
1
Vanhie, T. ; F. Tardif ; C. Swanton ; M. Cowbrough 2
1
1 University of Guelph; Government of Ontario
2
Glyphosate and group 2-resistant Canada fleabane (Conyza canadensis (L.) Cronq.) is a weed that is
spreading rapidly and becoming a great concern for farmers across Canada and around the world.
Managing herbicide-resistant Canada fleabane is proving difficult as farmers have a limited selection of
management strategies available to control this weed. This is especially true for soybean growers, to
whom Canada fleabane poses the greatest threat. In fields where this weed is left uncontrolled soybean
yields can be decreased over 90%. The agricultural industry realizes that new management solutions are
required to overcome herbicide-resistant Canada fleabane. This past summer, a trial in Delhi Ontario was
conducted to evaluate if an integrated weed management strategy that included cereal rye cover crops
alongside tillage and herbicide treatments improved the control of Canada fleabane. In some cases, when
rye was added with one other management tactic control of Canada fleabane exceeded 90%. The results
of this trial are promising, they show a new management strategy that can complement the control of
Canada fleabane when paired with other management strategies, and help diversify the methods used to
control this weed to prevent further resistance.

Theodore Vanhie (tvanhie@uoguelph.ca)

S152. Evolution of three herbicide defence strategies: Fitness costs of glyphosate resistance, escape,
and tolerance in an agricultural weed
*
Teitel, Z. ; C. Caruso
University of Guelph

In response to the application of herbicides, agricultural weeds can evolve multiple defence strategies,
including resistance, escape, and tolerance. Although each of these strategies are expected to incur fitness
costs, such costs are often not detected. We studied the costs of resistance, escape, and tolerance to
glyphosate herbicide in the agricultural weed Amaranthus palmeri grown in North Carolina soybean
fields. To estimate fitness costs, we regressed estimates of resistance, escape, and tolerance on four
components of female fitness measured in the absence of glyphosate. As to be expected if there is a cost
of tolerance, increased tolerance was associated with lower fitness: more tolerant populations produced
shorter inflorescences, fewer seeds per cm of inflorescence, and fewer seeds per plant. We also found
some evidence for a cost of resistance: although there was no relationship between resistance and three of
the fitness components measured, more resistant populations did produce shorter inflorescences. In
contrast to tolerance and resistance, we found no evidence of a cost of escape: there was no relationship
between escape and any component of fitness. Overall, our results suggest that the evolution of tolerance
to herbicide application is more likely to be limited by fitness costs than the evolution of resistance and
escape. However, more studies using other agricultural weed species are needed to determine how
widespread fitness costs for glyphosate tolerance are.

Zachary Teitel (zteitel@uoguelph.ca)

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