How to Control Corn Earworms in Sweet Corn Organically with BT

September 19, 2025

How to Control Corn Earworms in Sweet Corn Organically with BT

How to stop corn earworms from eating your ears of corn with BT organic pesticide.

Back in 2017 or 2018, when I grew corn for the very first time, I was so excited to pull back those husks and see what I had grown. Instead, I found corn earworms staring back at me surrounded by their frass! You can imagine how unsettling that was!

Ever since, I’ve been determined to do everything I can to avoid them. Corn earworms can devastate a sweet corn harvest, especially in small backyard patches. After losing nearly a third of my corn to earworms my first year, I’ve found an organic method that works: using Bacillus thuringiensis (BT). I'll link the video in the next section.

Earworm Credit: USGS Bee Inventory and Monitoring Lab

What Are Corn Earworms?

Corn earworms are caterpillars that feed on the kernels, usually at the tip of an ear of corn. Severe infestations can ruin entire ears, leading to major losses. This pest can be absolutely devastating even for commercial farmers; they're one of the driving forces behind the production of insect-resistant corn, along with corn root worms.

This is a pretty substantial agricultural pest, much like squash bugs and Japanese beetles. If the populations are high enough in your area, it's possible that you could have ears with several larvae feeding on the kernels. This is when extensive damage to the ears and yield occurs. If you live among commercial corn fields like I do, your corn crop will likely face heavy pest pressure.

Corn earworm populations can be high in small home garden corn patches when there are commercial corn fields nearby. This can lead to heavy earworm damage and a significant loss among sweet corn.

How to Spot Corn Earworm Damage

The corn earworm moth lays her eggs around corn silks. The small eggs hatch, and teeny tiny larvae climb down into the ear of corn through the silks. There, they begin feeding on the silks and developing kernels. You will typically find earworms towards the tip of the ears.

In order to monitor your ears for earworms, you can pull back the husk on developing ears to peak at the tip of the ears. If you see damage, check more ears of corn to determine the extent of the damage. Even if you're already seeing larvae, you can still treat the ears in order to stop damage from progressing further. Minor damage usually just results in the tip of the ear being trimmed off at processing; extensive damage may include poor kernel fill due to silk damage, or significant losses to the corn kernels especially if there's more than one earworm larvae within the husk.

This is what corn earworm damage looks like in a home garden. This is a white milling corn- a little different from sweet corn. Milling corns are used for flour, meal, and grits, for example.

The Organic Solution & Why It Works: BT (Bacillus thuringiensis)

I use Safer Brand Caterpillar Killer, which contains BT. This is a biological control that specifically targets caterpillars and larvae of many different species. By using BT on your corn silks, you're targeting the intended pest without spraying the entire corn patch; this saves time and money, while simultaneously protecting other species, such as beneficial ground beetles.

This year, I decided to grow Golden Bantam and Silver Queen Sweet Corn with a rotting hay bale. After all of that work to get the corn stalks to silking, I wanted to make sure that my harvest went well, with minimal damage from ear worms. I still need to update the original post or post a follow up, but I had a very successful corn harvest with this method! (2025 harvest, for future readers.)

Organic BT solution mixed into a spray bottle to treat the ears of corn for earworms, to prevent sweet corn losses in my home garden.

How to Apply Bacillus Thuringiensis to Sweet Corn Ear Silks

Mix BT (Bacillus thuringiensis) according to the instructions on your bottle. Different companies and formulations may have different directions, so I will not post them here. I pour some of my solution into a spray bottle as that seems to be the easiest method of application- especially since you can adjust the nozzle to reach ears.

Application Process:

Spray the corn silks directly.
Try to spray hours before a rainstorm, which will help to drive the solution into the ear.
For best results, spray:

At 7 days after silks appear.
Again at 14 days.
Optionally around day 18, just before harvest.

Sweet corn is usually ready around 20–21 days, so this schedule provides protection throughout the critical growth period. Even if you don't spray at day 18, it takes some time for eggs to hatch and for larvae to become large enough to cause substantial damage to the ear.

Freshly sprayed corn silk, this ear of corn should be pest free!

Spraying corn silks with Bacillus thuringiensis in order to stop corn earworm damage from occurring. This sweet corn patch was successful!

My Results with BT

In the past, I’ve lost up to 33% of my corn to earworms (mostly towards the beginning). This year, after spraying, the difference was dramatic:

I harvested somewhere close to 150 ears of sweet corn.
I'd say only 4 to 5 ears showed any earworm damage.
Damage was minimal, typically among the ears that were harvested later.
Most earworms that I spotted alive were between the husk and stalk, and there were MANY.
Regardless of the number of worms I spotted, they weren't inside the husks among the kernels- a huge success!

Look at how clean the tips of these ears of corn came out! Some had some damage due to me testing the kernels for milk stage for harvest.

This was only one round of processing; that's a very large storage tote! The earworm treatment was a success, and our goats absolutely loved eating all of the corn crop waste, including husks, silks, stalks, and leaves.

Cleaning and preparing a batch of corn cobs for blanching, so that the corn can be processed and frozen.
This nifty little tool cut the kernels right off the cob, making this process much easier and faster. One of my favorite $10 purchases! It's shaped like a peeler but has a curved blade area that follows along the cob.

Final Thoughts on the 2025 Sweet Corn Harvest (and Corn Ear Worm Battle)

This was an enormous improvement over my first year, and I consider it one of my best sweet corn harvests yet. I largely give credit to the rotting hay bale that I placed to grow the corn in, and the goat manure that lined the rows at planting. I linked to that blog post further up, and I highly recommend that method of sweet corn cultivation! Aside from that, the BT helped to protect the precious ears that I worked so hard to produce, all adding up to an excellent 2025 sweet corn harvest.

If you’re growing sweet corn and want to keep earworms at bay, BT is an excellent organic option. Y'all already know how much I love BT and its numerous uses in the garden, especially for Squash Vine Borer control. It’s affordable, easy to apply, and highly effective when timed correctly. With this method, I was able to freeze plenty of corn for my family, and next year I plan to expand the patch even more.

I don't think I'll be skipping out on sweet corn patches anymore! Here's to hoping for another successful sweet corn harvest during the 2026 season, hopefully with a patch 3-5x larger in size!

Look at all of these stripped, processed corn cobs! There's still corn left here, and the chickens were very grateful for this waste; not only did we yield lots of delicious, sweet corn from this harvest, but we had lots of waste that also became an enrichment toy (aka snack) for our flocks.

Corn stalks at silking, which is when corn earworms begin attacking. It was a stormy day, and I was getting a quick spray of BT in right as a thunderstorm was rolling in.

Young corn plant from this year's hay bale corn patch.

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How to Control Corn Earworms in Sweet Corn Organically with BT