Submitted to: North Central Weed Science Society US Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: December 10, 1998
Publication Date: N/A
Annual species are the primary weed problem in Midwest production systems, yet our understanding of the emergence characteristics of common weeds is limited. Experiments were initiated in 1997 at sites in NE, NW, SE, and SW Iowa to characterize the emergence behavior of nine weed species. Mean cumulative emergence ranged from 4% with fall panicum to 45% with common cocklebur. Common sunflower and velvetleaf cumulative emergence was 32 an 33%, respectively, whereas the remaining species ranged between 10 and 20% emergence. Emergence was first observed on March 30 at the NE location, whereas the latest initial emergence occurred on April 15 at the NW site. Averaged over the four sites, the sequence of initial emergence was: giant ragweed < common sunflower < velvetleaf < woolly cupgrass < giant foxtail < common waterhemp < ivyleaf morningglory < common cocklebur < fall panicum. Initial emergence of giant ragweed, common cocklebur, and velvetleaf occurred within a one week period, followed by a two week delay before emergence of woolly cupgrass. Initial emergence of fall panicum occurred approximately six weeks after giant ragweed. Mean time of emergence (MTE) was calculated to describe the emergence pattern over the growing season. The ranking of species by MTE's averaged across locations was: giant ragweed = woolly cupgrass < sunflower < fall panicum = cocklebur = velvetleaf < giant foxtail = waterhemp < morningglory. The MTE's for most species were relatively consistent across locations. However, the MTE's for giant foxtail, fall panicum, and waterhemp were at least 21 days longer at the NE site than at the other three locations. The sequence of emergence of the nine species was less variable among locations than cumulative emergence or MTE.