Be Prepared for Slugs

By John Tooker

As planting progresses, make sure you are prepared for slugs if weather continues to be wet and cool.

In recent days, cool and wet weather across most of the state is creating what appear to be ideal conditions for slugs. In some parts of Pennsylvania, the development of weeds suggests that are about two weeks or so ahead of normal; as a result, some southern counties have already experienced hatch of slug eggs. If the cool and wet weather continues, it will be prudent to watch no-till crop fields for slug damage as crops are planted and emerge (Figure 1).

Folks can encounter four species of slugs in their Pennsylvania crop fields (see our fact sheet on slugs ). The most problematic species for most of the state is the gray garden slug (Figure 2), which tend to be gray or tan-colored and can be discriminated from the darker marsh slugs by rubbing their backs with a piece of residue or a knife.

Figure 2: A gray garden slug in beautiful detail.

The mucus of a gray garden slug will appear milky, while the mucus of a marsh slug will appear clear. In western Pennsylvania, growers will also encounter dusky slugs, which are attractive little animals that can appear brown or even orange; their mucus also appears milky, sometimes with a tinge of orange.

We have a factsheet that describes scouting and management options for slugs , but our research indicates that managing slugs takes an integrated approach that should be planned well before spring planting. The most diverse rotations tend to experience the fewest slugs, and cover crops can be part of the solution by increasing rotational diversity. Many farmers believe that cover crops tend to be part of the problem, but our research indicates that cover crops can be helpful in the fight against slugs, including by planting green . 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 (Figure 3) can help suppress slug populations. These beetles can be suppressed by insecticide use, including seeds coated with insecticides.

Figure 3: The ground beetle Chlaenius tricolor, which can help significantly with slug control if farmers minimize their insecticide use, including insecticide-coated seeds.

To maximize their populations, rely on integrated pest management (IPM) to determine whether insecticides should be deployed against pest populations and avoid insecticide-coated seed. To prepare for potential slug damage, it can also be helpful to have some slug bait on hand to use as rescue treatments in portions of fields being damaged, but baits can be ineffective at times, particularly when rain keeps coming. Therefore, a long-term plan that relies on rotations, IPM, and natural enemies will be more sustainable, lower cost, and probably less frustrating.