By Anna Hodgson and John Tooker
As we get closer to planting season, we've been asked about best management practices to reduce slug damage at planting.
Why Did We Have Heavy Slug Damage in 2024?
In 2024, we had the worst slug year that many had ever seen. Many corn and soybean fields needed to be replanted due to slug damage. High slug populations resulted from multiple factors. First, the winter last year was mild. Slugs usually lay eggs in the fall, and adults die from cold temperatures over the winter. When the winter is warm, like last year, the adult slugs survive and lay more eggs in spring. This causes multiple egg hatches the following spring and juveniles are active for longer.
Another factor is planting soybeans early. Research from the Midwest has demonstrated the benefits of planting soybeans early; however, this research was not done in the presence of slugs. In the Midwest, tillage is still widely prevalent, and disrupting the soil with tillage disrupts slug lifecycles. If crops are planted before the soil temperature is ideal for germination and good growth, the seeds or seedlings can grow slowly for weeks, making them vulnerable to slug damage. In 2024, many farmers planted early and then conditions turned cool and wet, leading to slower crop growth and plenty of food for hungry slugs.
Planting Tips to Reduce Slug Damage
Our research indicates that managing slugs requires an integrated pest management (IPM) approach that should be planned well before the spring planting season. Our research also shows that higher ground beetle populations can help suppress slug populations (1). To attract these ground beetles and protect their populations, we need to farm with them in mind, including avoiding unnecessary insecticides. Our research shows that the most diverse rotations tend to experience the fewest slugs, and adding cover crops provides additional diversity while providing habitat and resources for slug predators (1). Below are considerations at planting to help reduce slug damage.
Plant crops at the appropriate soil temperature to allow faster germination and seedling growth. Smaller seedlings with slow growth are more vulnerable to slug feeding damage. The minimum three-day average soil temperature for corn and soybeans to germinate is 50°F (2). However, to achieve uniform stands, the ideal three-day average soil temperatures should be 60–70°F for corn and 77°F for soybeans (2). Waiting until soil temperature is optimum can help crops, especially soybeans, outgrow slug damage.
Research from the University of Maryland indicates that simply using row cleaners reduced the percentage of corn plants damaged by slugs (3). The mechanism behind this effect is that the row cleaners expose soil, allowing it to heat up faster, which gets plants growing (2). Additionally, at planting, ensure good furrow closure. If the furrow isn't closed well, it can create a "slug highway," allowing slugs to easily feed on seeds and seedlings (Figure 1).
More data from the University of Maryland indicates that using starter or pop-up fertilizer can reduce the damage corn plants receive from slugs (3). With starter fertilizer, placement seems to matter with in-furrow and banded applications of ammonium nitrate, reducing slug-damaged plants the most (3). Starter fertilizers get the plants growing and out of the ground quickly, and faster-growing plants experience less damage.
Managing Slugs Early in the Season
Scout to determine if insecticides, including insecticide seed treatments, are necessary for your fields. Following IPM and only using insecticides if necessary will give our ground beetle predators a better chance to control slugs and other pests.
Have some slug bait on hand for rescue treatments. If you are monitoring slugs and average 1–2 slugs per trap and there is severe slug feeding damage or dying seedlings, a slug bait is justified. Slug baits are most economical as a rescue treatment in portions of fields that are experiencing severe slug infestations. These baits can be ineffective, especially when it rains.
Source : psu.edu