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Slug Work

by Rebecca Picone

Slug crawls around on plant. PHOTO: NICK SLOFF

PHOTO: NICK SLOFF

Using no-till and other forms of conservation tillage has farmers accumulating large amounts of crop residue on their fields, which is good for water conservation and decreased soil erosion but provides excellent habitat for slugs. For many crops in Pennsylvania, particularly no-till grain crops, slugs are a serious pest. In spring and fall, when cool, wet conditions favor slug activity, crop damage is the worst, explains John Tooker, assistant professor of entomology whose research includes insect-plant interactions in agricultural systems.

“About 50 percent of the extension calls I received in 2009 were about slugs, and I had no idea how to answer these questions.” That dilemma led Tooker to search for answers.

Slugs damage crops by feeding on the seed or seedlings. They feed by scraping their radula (akin to a tongue) on the surface of crop seeds, roots, stems, flowers, and leaves, which causes strips in the leaves, termed “window-pane” damage. The slug problem led Tooker to a project involving geographic information system (GIS) technology and specialists from several departments.

“Our goal is to figure out better ways to manage slugs,” Tooker says. “If we can understand the soil type, the elevation and aspect of the soil, how long it’s been no-till, what the rotation is (to know how much residue might typically be there), and what crops are grown,” Tooker continues, “that data can help us understand where and when slugs will develop.”

Slug crawls under plant. PHOTO: NICK SLOFF

PHOTO: NICK SLOFF

Understanding how these factors work together may make it possible to develop a predictive model indicating when farmers could see slugs in their fields.

With this effort to understand slugs and gain an accurate prediction model comes GIS technology. Tooker explains, “Our effort to understand slug populations is being facilitated by the Center for Environmental Informatics.” Specifically, the GIS end of the project is being led by Doug Miller, who is the director of the center and earned his Ph.D. in soil sciences from Penn State.

“He’s a soil scientist,” Tooker says, “but he’s a soil scientist with a strong IT background, so he’s helping us develop an online tool that we hope to be able to use to understand slug populations.” Every layer of soil information associated with a specific field would be seen and interpreted, from the level of biological activity to biological presence or absence. Ideally, Tooker says, both infested and high-risk fields would be possible to identify. 

“So, five years from now my hope is to really be able to answer the phone from a grower who says, ‘I have slugs all over my fields!’ and have a better prescription that I can give to help them understand both why they had the slug problems and how they can make the slug problems go away.”