Conditions Are Right in Some Parts of Pennsylvania for Slugs

As spring progresses some Pennsylvania counties are seeing regular enough moisture that slug populations may threaten emerging corn or soybean plantings. You know if you live in one of these areas. If you do, it would be wise to get out and scout for slug damage. In Montgomery County, for example, Penn State Extension Educator Andrew Frankenfield is seeing in some emerging corn fields about 25% defoliation from slugs (Figure 1).

At this point in the season only a few management tactics hold potential to control slug damage, and the prospect of warm, sunny weather, as we see in most part of the state, will be the best hope for totally stopping the damage. In our experience, some early season slug damage may look bad, but as long as plants are growing and putting out new leaves, they are likely to out grow the damage and be just as productive as undamaged plants. In this way, slug damage can be similar to hail damage. If you happen to have portions of fields in which plants are dying from heavy feeding, metaldehyde-base baits can be useful, but these baits can be ineffective at times, particularly when rain keeps coming.

Our research at Penn State indicates that managing slugs takes an integrated approach that should be planned well before spring planting. The most diverse rotations tend to experience the least damage from slugs, and cover crops can be part of the solution to increasing rotational diversity. Many farmers believe that cover crops tend to be part of the problem, but our research indicates that cover crops, including by planting green, can be helpful in the fight against slugs. Other helpful tactics can include planting crops at appropriate soil temperatures and ensuring good furrow closure. Our research is also showing that strong populations of ground beetles can help suppress slug populations. These beetles can be suppressed by insecticide use, including seeds coated with neonicotinoid insecticides and broadcast applications of pyrethroids and organophosphates, so consider avoiding unnecessary insecticide use in fields that are perennially damaged by slugs. Our fact sheet on slugs describes scouting and management options.