Bryan Jensen
UW Extension
During 2015, I had several conversations with producers and crop consultants regarding spring slug activity in corn and soybeans as well as some late-fall damage in cover crops. We had, I think, an unusually warm fall and certainly a warm winter. Both events can enhance slug survival. However, our spring weather will arguably have more impact on damage potential in seedling corn and soybean. Although it is hard to estimate what the 2016 damage potential will be, it will be worth your time and effort to do some spot-checking for damage this spring. Especially in area, you noticed problems last year.
Because slugs are nocturnal feeders and often hide under crop residue and/or soil clods during the day, scout for evidence of crop feeding on the lower leaves. Slugs have a “rasp-like” mouthpart and damage plants by scraping off leaf tissue. On corn, feed scars are usually linear in appearance. The upper or lower cuticle may remain intact causing a “window-pane” effect. Eventually the cuticle will weather away and leave linear holes in the leaf. Feeding in soybean can be more severe because slugs will feed completely through the cotyledon and/or hypocotyl causing severe stand reduction
Slugs require a cool, moist habitat to survive which is why they are primarily a pest in no-till conditions. Prevention, in the form of habitat disruption, can significantly control slugs and manage future populations. During the 2016 planting season, anything you can do to bury residue will help………assuming it is compliant with conservation plans and other erosion concerns. People have also had success using strip-till but effective residue within the row is important.
Planting date can also impact slug damage. Early planting into areas of know slug activity can give the crop a head start because older plants are less susceptible to slug feeding. If the cropping rotation allows, switching to corn may provide added benefits because corn’s growing point is located below ground until V6. The growing point of soybean is above ground after emergence and therefore significantly more susceptible to early season feeding. Regardless of crop, make sure the seed furrow is completely closed or slug feeding may result in higher stand loss, even in corn. Additionally, an open seed furrow provides additional habitat beneficial for slug survival.
Insecticides will not control slugs. Either they are nontoxic if ingested or because of the slug’s ability to produce slime making the contact insecticides ineffective. Attempting to try insecticides is likely to increase slug damage because those products kill non-target beneficial insects like ground beetles. Anecdotal information suggests that high salt fertilizer applied at night may work. However, this control tactic is not based on sound science, is not always effect and these fertilizers may be phytotoxic to plants.
Mollusicides applied as a bait can be an effective rescue treatment but should not be relied on as the only control tactic. Because of the low commodity prices in 2016, economics will be a primary concern. Spot applying to problem area may make baits more feasible. Products that include the active ingredients metaldehyde (corn only), sodium ferric EDTA and iron phosphate are labeled. Follow labeled use rates and make sure the product is distributed evenly throughout the treated area.