Submitted to: Seed Production Research at Oregon State University
Publication Type: Experiment Station
Publication Acceptance Date: 3/31/2007
Publication Date: 7/30/2007
Citation: Gavin, W.E., Banowetz, G.M., Griffith, S.M., Mueller Warrant, G.W., Whittaker, G.W. 2007. Earthworms and their impact on slug control. Seed Production Research at Oregon State University.Department of Crop & Soil Science Ext/CrS 126 04/2007 P 22-27. Interpretive Summary: Increases in the number of night crawlers and earthworms have occurred due to improved farming methods and drainage in grass seed fields of western Oregon. The use of earthworm toxic chemicals also has been reduced. Some field observations suggested that the increased number of earthworms, generally associated with improved soil fertility, have resulted in reduced efficiency in controlling slugs that damage new seedlings in these fields. We set up controlled conditions in fields to determine whether earthworms were removing slug bait. Our study showed that twenty percent of applied baits were removed nightly by the common nightcrawler, reducing the chances of controlling the gray field slug, Derocerus reticulatum. Less than twenty-four percent of available slugs found and consumed enough poison from remaining baits when earthworms were active. This study demonstrated the need to optimize application of slug baits to coincide with times of minimal earthworm activity.
Technical Abstract: Increases in the anecic earthworm species, Lumbricus terrestris L., have occurred in western Oregon grass fields due to increases in surface residue since the phase-out of open field burning. The use of earthworm toxic chemicals has been reduced through concerns for other important vertebrate and invertebrate species. As a consequence, earthworm numbers have increased dramatically. Anecdotal evidence suggested that earthworm removal of baits used to control slug damage in grass seed production fields seriously reduced the amount of slug control each application provided. This study quantified earthworm removal of slug bait under controlled field conditions. Twenty percent of applied baits were removed nightly by the common nightcrawler, reducing the chances of controlling the gray field slug, Derocerus reticulatum. Less than twenty-four percent of available slugs found and consumed enough poison from remaining baits when earthworms were active.