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Trade-offs of controlling slugs in no-till

Tom J. Bechman A close up of a slug resting on a persons hand
SLIMY: Slugs are a challenge in no-till as they will munch on your just-planted corn and soybeans, leaving behind uneven stands and bare spots.
These critters are a challenge, and controlling them requires a change in mindset.

No-till has many benefits. Just ask a grower who’s been doing it, and they will tell you that. But it also presents challenges, and one of those reared its ugly head last year — at least in Pennsylvania: slugs.

Anecdotally, growers across the state reported slug issues that got so bad that some had to replant not once, but twice.

“Unfortunately, there’s no silver bullet” to dealing with slugs in a no-till system, said John Tooker, professor of entomology at Penn State. But that doesn’t mean you can’t do anything about it.

Last year was an especially challenging year for slugs, he told a group of growers gathered for a recent crops conference at the Lancaster Farm and Home Center. This was because the heavy snow that fell over winter provided enough insulation for adult slugs to overwinter and lay eggs in spring, and this caused problems for growers in May and early June.

Typically, adult slugs die from the first hard frosts in fall, even if they are able lay eggs.

With more than 70% of corn and soybeans grown no-till in Pennsylvania, this also provides a good environment for slugs to thrive.

“Fields that aren’t tilled have a nice, stable habitat for slugs, and that’s why they develop there,” Tooker said. “Tilling doesn’t provide that stable environment unless a grower is growing strawberries under black plastic. When we have long-term no-till, we have slugs.”

A common misconception is that slugs are insects. But slugs are mollusks and are more closely related to clams than insects, Tooker said. This is an important point, he said, because insecticides used to control other pests are not effective against slugs. At the same time, these insecticides can knock out the beneficial pests that could control slugs naturally, creating a real no-win situation for growers.

Slugs are voracious eaters and will munch on almost anything. But canola, soybeans and brassica cover crops — radishes, turnips, rapeseed and mustards — are their favorites, Tooker said. They will also feed on corn, but only if there is no other option. This is where having a cover crop, or even some weeds, can be effective because it gives slugs another option over corn.

But this requires some forethought: Is your slug problem bad enough that you’ll allow some weeds to better control them?

No easy answers

Tillage is always an option to control slugs, especially using a moldboard plow. This will help bury the slug eggs so deep that they won’t be able to reach the surface.

But with so many growers doing no-till now, some for decades, this is not a practical solution for some growers.

Baits are another good option for slugs, but Tooker thinks they should only be used sparingly. Metaldehyde baits are pellets that can be spread. Some growers spread them with potash, he said.

The goal is to spread at least 10 pounds per acre, or 4 to 6 pellets per square foot. Some growers even spread it in bands over a row. Tooker said that slugs prefer these pellets over other plants, so they can be effective. The only exception is soybeans, as slugs will prefer soybeans over bait.

Another issue with these baits is that they are water-soluble. Slugs will come out in droves when it is wet. Applying these baits after a good rainstorm can be effective, but if more rain is in the forecast, the bait can be washed away, limiting your time to get it applied.

“These baits are best used for targeted rescue treatments,” Tooker said. “So if you have plants dying, corn and soybean fields, then baits are a great choice. If the plants aren’t dying, I wouldn’t use the baits right away. Just keep your fingers crossed, hope for some nice weather that will get those plants growing and get them out of the ground, and then they can outrun the damage.”

‘Rule of 3’

Through farmer networks, another solution has developed, but you want to think very hard before doing it.

The solution is using nitrogen to kill slugs. The concept involves mixing 30% nitrogen 1-to-1 with water, spraying it when it’s dark when slugs are most active, and doing it three nights in a row. Some growers call it “the rule of 3.”

Tooker said this method is risky, but it’s been studied by Galen Dively, former entomologist at the University of Maryland, who found that 10 gallons of 28% urea in 10 gallons of water knocked back slug populations by 75% on average. Tooker said this likely only gives temporary relief, and with nitrogen prices much higher than before, it might not be a good option, but it can work.

“So if you’re really struggling, and you know good weather is coming, this might be an option,” he said.

Preserve the predators

One of the benefits to no-till is that the stable habitat provides a great place for slug predators — ground beetles, firefly larvae and soldier beetle larvae — to thrive. It’s made even better by planting cover crops.

Ground beetles are especially effective, Tooker said, as the larvae and adults will both feed on the slugs.

“To make predators most effective, though, we have to think about our pesticide use, particular our insecticide use,” he said. “I often encourage farmers to use integrated pest management to manage their insect populations.”

So scout fields before you decide to spread, and see if you have enough pests to justify using an insecticide.

“If you do have a pest population that needs insecticide, then use it, rather than just tank-mixing an insecticide and blindly using it whether you know if you have an insect problem or not,” he said.

Noenicitinoid seed coatings are effective at killing bugs. The water-soluble coating is taken up by the plant when it starts to emerge, and the bugs feed on the plant, killing them. But it’s only effective if the bugs are around in the first place. This is an important point that Tooker said growers should think about if they have a slug problem.

“If you’re suffering from slugs perennially … I would recommend removing the coating from those seeds and plant something else into those fields because slugs are only going to be in a position to succeed when the insecticide is there,” he said. “My bottom line is to manage for the pests that you have.”

Planting green is another good tool for managing slugs as you will be planting your cash crop into a living cover crop in spring that has been rolled or is still standing.

Remember, the cover crop, especially cereal rye, provides good habitat for slug killers, but it is also an alternative plant for slugs to munch on. It also involves quite a bit of management, so you might want to talk to an experienced farmer before diving in.

TAGS: Management
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