Initial dates of weed emergence

Timing of weed emergence varies both from year to year and also across the state. The table provides information on the initial date of emergence of five early weed species at locations across Iowa. Giant ragweed, one of the earliest emerging summer annuals found in crop fields, initiated emergence in the last week of March or first week of April in both 1998 and 1999. At most locations giant foxtail began emergence about 4 weeks after giant ragweed, but at the SE (Crawfordsville) location there has been only a 2-week difference in initial emergence of these species. Additional information concerning weed emergence is available at the ISU Weed Management Web site at www.weeds.iastate.edu/

Date of initial emergence for five weed species in 1998 and 1999 across Iowa.1

SE SW Central NE NW
Species 1998 1999 1998 1999 1998 1999 1998 1999 1998 1999
Giant ragweed 3/29 3/28 3/29 4/4 3/29 3/28 3/29 4/4 NA ?
Annual sunflower 3/29 4/4 3/29 4/11 4/5 4/16 3/29 ? 4/12 ?
Woolly cupgrass 4/12 4/4 4/19 4/11 4/19 ? 4/26 ? 4/26 ?
Velvetleaf 4/5 4/4 4/12 4/11 4/12 ? 4/12 ? 4/12 ?
Giant foxtail 4/12 4/11 4/26 ? 4/26 ? 4/26 ? 5/3 ?

? indicates first emergence not observed in 1999 at time of printing.

1Locations: SE, Crawfordsville; SW, Lewis; Central, Ames; NE, Nashua; NW, Sioux Center.

This article originally appeared on page 46 of the IC-482 (7) -- April 26, 1999 issue.

Updated 04/25/1999 - 1:00pm