Occurrence of common milkweed (Asclepias syriaca) in cropland and adjacentareas

Interest in the population dynamics and geographic distribution of common m ilkweed (Asclepias syriaca L.) has recently increased due to the importance of common milkweed in the life cycle of the monarch butterfly (Danaus plex ippus). A survey of common milkweed occurrence in various habitats was cond ucted in Iowa in June and July of 1999. Common milkweed was found in 71% of the roadsides and approximately 50% of the corn (Zea mays L.) and soybean (Glycine max L. Merr.) fields. Corn and soybean fields had 85% fewer patche s than roadsides. Conservation reserve program fields had the greatest aver age area infested. While common milkweed was frequently found in corn and s oybean fields, average frequency and patch sizes were much greater in noncr op areas. (C) 2000 Elsevier Science Ltd. All rights reserved.