Proceedings of the Sixty-first Annual Meeting of the Northeastern ...

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DO ECOLOGICAL INSIGHTS INFORM CONYZA MANAGEMENT? D.A. Mortensen,
J.T. Dauer, W.S. Curran, The Pennsylvania State Univ., University Park, and M.J.
VanGessel, Univ. of Delaware, Georgetown.
ABSTRACT
Over the past four plus years we have conducted numerous life history,
dispersal, and simulation studies and on-farm surveys to understand the nexus of
glyphosate resistant horseweed (Conyza canadensis) population dynamics and
management. During that time the spatial extent of this invasive genotype increased
approximately five fold. This rapid invasion speed can be explained by long-distance
propagule dispersal and high recruitment success. In fact, we have observed seeds
reaching the atmospheric boundary layer. Aerial sampling has detected Conyza seed at
altitudes in excess of 100 meters above the ground surface. The implications of such
findings are profound, once aloft at such altitudes it is likely that seed could travel tens
of kilometers in a single day. Given that seed are released over a period of some six
weeks, there is ample opportunity for very long-distance seed movement. The practical
implication of these findings is that fields and farmsteads are far more highly
interconnected than previously thought. Effectively, a grower could inherit the downside
consequences of poor management from a neighbor many kilometers away. Another
implication of these findings is that buffer distances between "invaded" and “uninvaded”
farmsteads must be sufficiently large to limit the possibility of resistant horseweed
gaining a foothold in new farms or farming regions. Finally, real costs have been
incurred by this resistance outbreak. In the region where the on-farm surveys are being
conducted, the cost of weed control has increased significantly as the efficacy of
glyphosate has decreased. It is clear that successful approaches at minimizing the
spread of the plant will require an area-wide approach. It may also be the case that
such an approach will be required once a local growing region has been invaded.
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