Got Slugs? | Weekly Crop Update

Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

I have seen a few corn fields with slug feeding injury. Slugs use their rasping mouthparts to feed on corn leaves, giving them a shredded appearance. Under heavy slug pressure, slugs can kill seedling plants resulting in stand reductions. No-till fields, fields with high organic matter, and with a history of manure tend to be at greatest risk, especially if the field has a history of slug activity. The best cultural control practice to manage slugs is tillage but this is counterproductive to no-till and conservation tillage practices. Planting early, before slug egg hatch occurs can also allow plants to get a head start. However, what is early this year wasn’t early last year and probably won’t be considered “early” next year so this is a moving target. Lastly, anything that will promote seedling vigor and growth will also give plants an advantage, but under heavy pressure, slugs can still outcompete seedling plants.

There are several chemical control options available as rescue treatments, such as metaldehyde baits (Deadline M-Ps), Sluggo, and Iron Fist. There are no established thresholds for when a rescue treatment is warranted. However, if slug injury is severe and the weather is unfavorable for corn growth (cool and wet), a control measure may be necessary.

Here are several links to our efficacy trials evaluating these products:

https://cdn.extension.udel.edu/wp-content/uploads/2013/12/29043617/2016-Season-Insect-Management-Reports-final.pdf (page 4)

https://s3.amazonaws.com/udextension/ag/files/2013/12/Chemical-Management-of-Slugs-in-No-Till-Corn-and-Soybean-Systems-final.pdf

Last year, I followed two plants to visually show how metaldehyde baits can reduce slug injury on seedling corn. In this particular field, about half of the field was treated with Deadline M-Ps at 10 lb/A and the other half was untreated. I flagged two plants with similar levels of slug feeding injury, one in the treated portion of the field and another in the untreated. I then went back every week and took a picture of each of the plants to see how the plant was responding to the treatments (treated versus untreated).

Does Slug Bait Work?
Photos began on May 13, 1 day after Deadline M-Ps application, and ended on May 27, 15 days after treatment.

To determine if your field is at risk for slug injury and to determine the species and abundance of slugs you have, you can sample fields for slugs using shingle trapping methods or residue sampling prior to planting.