We have been receiving more reports this season than usual of slug damage in corn and soybeans, either through plant feeding or through seed feeding in open seed trenches (Figure 1). Emerging corn plants are less susceptible to lasting damage than soybean plants because the growing point of corn is below the ground when the plant emerges, so the corn will continue to put out new leaves, even if defoliated. In soybean, the growing point is within the emerging cotyledons – feeding here can damage the growing point, killing the plant. On the other hand, soybeans can tolerate more stand loss than corn without losing yield, because the existing plants bush out and become larger, up to a point. For advice on soybean replant decisions, visit https://agcrops.osu.edu/newsletter/corn-newsletter/14-2021/soybean-stand-evaluation-and-re-plant-decisions
Not many treatment options are available for slugs in corn and soybean. The most effective treatment to date is baited pellets containing metaldehyde. Look for a concentration between 3.24 and 4%. The application rate for most metaldehyde-containing poisonous baits is 10 pounds per acre for soybeans and 25 pounds per acre for corn. Both uses are labeled in Ohio but are not labeled for both crops in all states. Spread pellets at a rate of 5 – 12 pieces per square foot. The other alternative active ingredient, iron phosphate, has lower effectiveness but has the advantage of being organic-approved. In either case, the slugs must eat the pellets for the product to work. The pellets break down when wet, so try to apply them to ground that isn’t sopping wet, and with at least a few days before the next predicted rain.
The baits appear to work better when slugs are small so there is less value to applying later in the season when the spring juveniles have grown. Slugs are nocturnal so they’re harder to spot during the day. To get a feel for your slug population look for the adult slugs by carefully examining the soil surface, and brushing aside residue and debris (Figure 2). You can put down square-foot sections of plywood at a few locations in the field (marked with flags) and check under them periodically in the morning. Unfortunately, we do not have a threshold recommendation for slugs, but monitoring the population will give you a feel for whether the problem is increasing or decreasing. Slugs will be present in the field all season, but at a certain point, the plants will have grown past being susceptible to meaningful damage.
For more information on slug management, visit our field crop slug factsheet at https://aginsects.osu.edu/sites/aginsects/files/imce/Slugs%20on%20Field%20Crops%20_%20Ohioline.pdf
This season we are conducting slug monitoring in 13 Ohio counties in a United Soybean Board-funded project to better understand slug populations across the state and region.
The map below shows the average number of slugs found under the shingle trap in each county from June 3rd – June 9th (Figure 3). Over the past week, the average number of slugs in some counties increased. Seneca County had the highest average of 7.0 slugs/shingle over the past week, followed by Wayne County with 5.0 slugs/shingle. The majority of counties in Ohio continue to report low numbers of slugs under the shingle traps; however, slug activity varies greatly from field to field, and all no-till fields planted recently should be scouted for slugs.
Slug Monitoring in Ohio
June 3rd – June 9th
