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Title: OCCURRENCE OF COMMON MILKWEED (ASCLEPIAS SYRIACA) IN CROPLAND AND ADJACENT AREAS OF IOWA

Author
item HARTZLER, ROBERT - IOWA STATE UNIVERSITY
item Buhler, Douglas - Doug

Submitted to: Weed Science Society of America Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 2/9/2000
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Interest in the population dynamics and geographic distribution of common milkweed has recently increased due to the importance of common milkweed in the life cycle of the monarch butterfly (Danaus plexippus). Distribution and patch characteristics of common milkweed in Iowa were determined by a plant census conducted during June and July of 1999. A random, representative sample of the state was generated by selecting forty 100 km**2 cells using a coordinate reference system. Within each 100 km**2 cell, ten arbitrarily selected 0.5 ha (50 by 100 m) areas were surveyed for common milkweed. Common milkweed was found in 71% of the roadsides and approximately 50% of the corn and soybean fields surveyed. Pastures had the lowest infestation rate (28%) of the habitats surveyed. Roadsides had 48 common milkweed patches ha**-1, whereas corn and soybean fields averaged 7 patches ha**-1. Land maintained in the Conservation Reserve Program (CRP) had a relatively low number of patches (9 ha**-1); however, the patches in this habitat were larger than those in other settings. This resulted in CRP having the highest percentage (2%) of area infested with common milkweed of the habitats surveyed. Land maintained in corn, soybean, or pasture had the lowest average area infested (< 0.3%); however, these land uses encompass 78% of the Iowa land mass and therefore may be an important resource for monarch butterflies. This research provides information about the distribution of common milkweed in Iowa and areas with similar climate and land use patterns. However, additional information is required before an accurate assessment can be made of the impact of genetically modified crops on monarch butterflies.