Look for signs of this troublesome mollusk this spring
They’re slithery, slimy and they love to make a smorgasbord of your crops. The drab and inconspicuous slug continues to increase its rank of pests you should scout for and monitor in your corn and soybean fields.
“Slugs are actually not an insect; they are a mollusk,” says Nick Seiter, University of Illinois Extension field crops entomologist. “That has real implications for how they behave, their life cycles and ultimately how we manage them.”
Slugs are soft-bodied and legless. They are white, gray or black and can range in size from ½" to 4". They overwinter as eggs in fields and hatch during the spring. Since they are nocturnal, they attack fields at night or on cloudy days. During the day they often hide under soil clods and crop residue. Their main food source is decaying organic matter and plant foliage.
What attracts slugs to your fields? Cool and wet conditions, Seiter says. Related, reduced tillage, no-till and certain cover crop systems can lead to larger slug populations.
“Cool conditions that slow crop development will give slugs more time to do damage to crops and ultimately reduce the crop stand,” he says. “Where we especially see issues with slugs is in soybeans. They really like to feed on those germinating seeds and on the cotyledons.”
LOOK FOR SLIME
Slugs feed on crops within a month of planting. They either eat seeds or scrape the surface of plant tissue, causing a shredded appearance.
“The feeding can often be mistaken for flea beetle feeding in corn,” says Marc Eads, owner of Spearhead Agriculture and Management. “They do most of their damage in the early part of the growing season.”
Slugs secrete a protective layer of slime over their bodies. Look for silver slime trails on plants and on the ground, as this is a telltale sign of pests. Signs of slugs are often apparent before you actually see them.
In corn, slug damage is common from VE to V8. In soybeans, damage typically occurs VE to V2. To scout, examine 20 plants in five separate locations. Note the number of damaged plants and estimate the percentage of defoliation.
SLOW THE SLUGS
Managing slugs is difficult because of their uniqueness and a lack of effective chemical treatments.
“Insecticides are not effective,” Seiter says. “In fact, an insecticide may hurt some of the beneficial insects in your fields. There are some slug-specific baits, but they tend to be expensive and hard to find.”
While the pest is troublesome, there is no actual economic threshold. If you have extensive slug damage that reduces your crop stand, he says, replanting might be necessary. If that’s the case, hold off on replanting until soil dries out and warms up, which will reduce the slug population.
Tillage disturbs their habitat and can decrease your risk of replant.
“The most reliable management tactic for slugs is to plant into a warm, dry seedbed, which is not always an option,” Seiter says. “However, by understanding conditions that are likely to lead to slug problems, you can be better prepared to address them when and where they occur.”
Fast Facts About Slow Slugs
- Slugs are essentially shell-less snails — they actually have a remnant of the shell within their body.
- A hermaphrodite, slugs are both male and female at the same time.
- Slugs have four tentacles: two eyes and two antennae.
- The slimy mucus slugs secrete aids them in locomotion.
- Because they’re soft-bodied with no shell, top predators include frogs, snakes, birds, beetles, spiders and more.
Read more in the Unspoken Truths About Pests series.
