Survey of Giant Ragweed Distribution and Spread in the North Central Region Regnier, E., C. Holloman, S. K. Harrison, M. Loux, R. Venkatesh, R. Ford, R. Taylor*, & F. Diekmann Ohio State University, Columbus, OH *Texas A&M University, Temple, TX

BACKGROUND North American native riparian species Increasing problem in crop fields in the last 30 years

(1852) Date of first collection for herbaria

Date of reported herbicide resistance

Hypothesized steps in spread of GRW Spread from E to W Adaptation from riparian to upland habitats Spread from non-crop borders into crop fields Evolution of prolonged emergence period Facilitated by reduced tillage and POST herbicide

Survey of North Central States Certified crop advisors Distributed online by ASA July 2013 Exploratory data analysis – Mapping – Correlation analysis

In terms of management, how would you rate giant ragweed?

r MD = correlation with management difficulty, p < 0.05 Management Difficulty

Has herbicide-resistant GRW been suspected or confirmed (to ALS-inhibitors, to Glyphosate, to both)? Yes, confirmed Yes, suspected

Has herbicide-resistant GRW been suspected or confirmed? Management Difficulty Yes, confirmed Yes, suspected Corn, soybean, wheat: r MD =.19 to.28 Cotton: ns

What percentage of noncrop acreage has giant ragweed present? r MD =.22

What percentage of crop acreage has giant ragweed present? r MD =.22

How long ago was GRW first observed in areas outside of crop fields? r MD = ns

How long ago was GRW first observed in crop fields? r MD = ns

In which non-crop environment did giant ragweed first appear?

In which non-crop environments have you observed giant ragweed?

Number of checked non-crop environments r MD =.18

Presence of giant ragweed in waterways r MD =.19 % of respondents answering yes

Presence of giant ragweed in fencerows % of respondents answering yes r MD =.11

Correlation of GRW presence in non-crop habitat and resistance

When does giant ragweed first emerge as seedlings? r MD = -.22

Giant ragweed emergence period ( months ) r MD =.19

On what percentage of crop acreage is each of the following practices used?

Correlation of herbicide practice with GRW management difficulty

Correlation of perceived GRW resistance source with management difficulty

Summary Hypothesized steps in spread of GRW Spread from E to W – from center outwards Movement from crop borders into crop fields – Railroads, fencerows, ditch-banks, waterways Adaptation to upland habitats – for over 20 yrs Evolution of prolonged emergence period – Earliness and duration of emergence associated with increased management difficulty Facilitated by reduced tillage and POST herb. – Reduced tillage associated with increased difficulty – POST – no association with management difficulty

Thank you to all those who reviewed our survey questions and participated in the survey! Funded by USDA - NCIPM