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Title: Giant ragweed emergence across the Midwestern United States

item CLAY, SHARON - South Dakota State University
item Forcella, Frank
item Davis, Adam
item SPRAGUE, CHRISTY - Michigan State University
item DILLE, J - Kansas State University
item REICKS, GRAIG - South Dakota State University
item RAMIREZ, ANALISA - Kansas State University
item TAYLOR, ERIN - Michigan State University

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 10/24/2012
Publication Date: 10/24/2012
Citation: Clay, S.A., Forcella, F., Davis, A.S., Sprague, C., Dille, J.A., Reicks, G., Ramirez, A.H., Taylor, E. 2012. Giant ragweed emergence across the Midwestern United States [abstract]. ASA-CSSA-SSSA Annual Meeting Abstracts. ASA-CSSA-SSSA Annual Meeting. Oct. 21-24, 2012, Cincinnati, OH. Available:

Interpretive Summary:

Technical Abstract: Predicting weed emergence timing from the seed bank plays a critical role in scheduling early season post-emergence weed management operations to achieve the greatest efficacy. This study used common source seed (Illinois) in 13 site years in Illinois, Michigan, Kansas, and South Dakota to examine the importance of site and climate variability by year on giant ragweed (Ambrosia trifida) emergence. Thermal time, hydrothermal time, and modified hydrothermal time models were used with the Weibull equation to fit emergence data. Thermal time used GDD with a temperature base = 1 degree C accumulating from January 1 of each year. Hydrothermal time incorporated soil dryness when soil water potential was too low; thermal time did not accumulate. Modified hydrothermal time incorporated soil wetness as a parameter and thermal time did not accumulate if soil water potential was above -33 kPa. Regional emergence was not well estimated by calendar day; however, thermal time had a R2 = 0.79, indicating that soil temperature had a large influence on emergence. Incorporating soil dryness with hydrothermal time improved the regional estimate although minimally (R2 = 0.81). Investigating emergence within a site by combining year data sets often had poor model fit. However, both the hydrothermal and modified hydrothermal times did very well for a single year and site. Soil temperature and wetness prior to and during emergence had a large impact on start and end of emergence. The data from the current research indicate that while not robust across the region, emergence forecasts for giant ragweed under differing soil management scenarios can be predicted. If very wet conditions are prevalent in the spring, the modified model, using an upper boundary for water potential may be appropriate to better model seedling emergence.