As spring progresses, some Pennsylvania counties are seeing enough precipitation that slug populations are threatening emerging corn and 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. Our extension educators who are scouting for slugs are reporting high populations in many areas, but particularly fields in Adams, Columbia, and Montgomery Counties (Figure 1).
At this point in the season, only a few management tactics hold potential to control slug damage, and warm, sunny weather will be the best hope for slowing slugs and their damage. In our experience, some early-season slug damage may look bad, but if plants are growing and putting out new leaves, they are likely to outgrow the damage and be just as productive as undamaged plants. In this way, slug damage can be like hail damage. If you happen to have portions of fields where plants are dying from heavy feeding, slug baits with active ingredients of metaldehyde or iron can be useful, but these baits are imperfect—they tend to be expensive and can be ineffective, particularly when rain keeps coming.
Because slug control can be frustrating, some growers have experimented with home remedies. Chief among these is spraying crops at night with nitrogen solutions, which act as a contact poison and burn slugs. A common approach is to use a 30% urea-based nitrogen solution (or something similar), mix it with an equal amount of water, and apply 20 gallons per acre. This tactic can be repeated a few nights in a row to maximize its effectiveness, because nitrogen solutions provide no residual control and all slugs in a field will not receive a killing dose in a single application. This approach should be used with caution because the nitrogen is likely to burn crop plants, possibly causing less damage than slugs, and use of nitrogen outside of a nutrient management plan may raise other concerns.
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 planting green (i.e., planting a cash crop into a green cover crop), can be helpful in the fight against slugs. Other helpful tactics can include using row cleaners and pop-up fertilizer, ensuring good furrow closure, and planting crops at appropriate soil temperatures—all these practices help promote early season growth so your crops get out of the ground quickly and grow more quickly that slugs can feed.
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 damaged by slugs. Our fact sheet on slugs describes scouting and management options.
