Nightcrawlers and Giant Ragweed
Dennis Epplin, crop systems educator

Weed scientists Emilie Regnier and Kent Harrison and entomologist Clive Edwards, at The Ohio State University, recently wrote this summary of research that they have conducted on giant ragweed, also known as horseweed, and nightcrawlers, also known as earthworms. Their work explains the reason that giant ragweed is so persistent. Here is a quick look at their research findings and conclusions.

A Summary of Research Results Thus Far

• In plots excluding vertebrate seed predators, nightcrawlers began collecting and burying giant ragweed seeds immediately after their dispersal, thus shortening the exposure time of seeds on the soil surface to as little as 1 or 2 days. By 20 days after dispersal, the earthworms had collected and buried 95 percent of giant ragweed seed in their burrows and middens.
  
  
• Earthworms buried seeds from 0.2 to 8 inches deep. Most of the seeds were buried in the upper 4 inches of the soil, which represents the depth limit from which giant ragweed seedlings can emerge. But, some seeds were buried below 4 inches, where giant ragweed seeds tend to remain dormant.
  
  
• Earthworms buried over two-thirds of giant ragweed seeds dispersed naturally by a giant ragweed stand. An earthworm burrow contained an average of 127 seeds, and earthworms buried an estimated total of about 500 seeds per square foot.
  
  
• Giant ragweed seedlings were aggregated in nightcrawler burrows in no-tillage corn and soybean fields in Ohio, Indiana, and Illinois—
  indicating that when nightcrawler and giant ragweed occur together, the earthworm is likely to bury giant ragweed seeds and thereby
  influence seed survival and seedling distribution.
  
  
• Nightcrawlers collected and buried seeds of 10 other weed and crop species by the same behavior but exhibited preferences among them. Giant ragweed, bur cucumber, and sunflower seeds were
  preferred over common cocklebur and tall morning glory seeds.

Summary and Conclusions
Our research has shown that nightcrawlers forage actively for giant ragweed seeds, that they are capable of burying the majority of the seed produced by a stand of giant ragweed, and that they distribute seeds over a range of depths thus influencing seed dormancy and seedling emergence. The research also suggests that seed burial by nightcrawlers protects seeds from predation and exerts a strong influence over giant ragweed populations in subsequent years. With the introduction of nightcrawlers in the U.S., it appears that giant ragweed has acquired a new mechanism of spreading and survival, which may help explain its persistence and expansion as a major weed problem.

Websites Worth a Bookmark
Annette Campbell, communications and marketing educator

If you use the internet to get the latest information for your farm
operation, here are two websites worth bookmarking in your browser:

• Extension’s Pesticide Safety Education Program website has been
  redesigned to provide you with more complete information. The site
  features tips and fact sheets, a directory of training manuals, training schedules, certification information, and a comprehensive list of
  resources. The site also contains the current issue of the Illinois
  Pesticide Review as well as past issues. Bookmark the site in your web browser for handy reference: http://web.extension.uiuc.edu/psep/.
  
  
• The SI Agriculture website contains information of interest to farm
  families in southern Illinois. You’ll find plot results from the Ewing
  Demonstration Center, information on starting an agritourism
  operation, a list of producers who have Illinois Heifer Development
  Program heifers for sale, as well as links to other websites such as the Certified Crop Adviser site and the Farmdoc site. Bookmark the
  SI Ag site at http://web.extension.uiuc.edu/regions/ag.
  
  
  
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