Cutworms are night-hunting pests that can wipe out your asparagus if you don’t catch them early.
Knowing the signs helps you spot them fast, tell them apart from other issues, and protect your crop before it’s too late.
What Are Cutworms and Why Do They Target Asparagus?
Cutworms are baby moths—well, technically the larval stage of night-flying moths.
The black cutworm (Agrotis ipsilon) is one of the worst offenders. They’re chunky, gray-brown, up to 2 inches long, and look a bit greasy.
Touch them and they curl into a “C” like they’re playing dead.
Asparagus is an easy target for them because:
- Young spears are tender and basically a gourmet snack.
- Spring growth lines up perfectly with peak cutworm feeding season.
- Asparagus beds stick around year after year, giving cutworms a permanent home.
- Spears grow right at soil level—prime real estate for ground-hugging larvae.
Primary Signs of Cutworm Damage in Asparagus
If cutworms move into your asparagus bed, they’ll leave some pretty obvious calling cards.
Here’s what to look for:
Spears cut clean at ground level
This is their signature move.
Cutworms bite through spears like someone snipped them with garden shears.
It usually happens at night, so you’ll spot the fresh “beheadings” first thing in the morning.
Spears growing crooked or curled
If a cutworm chews one side of a spear, that side stops growing right.
The other side keeps going, and the spear bends or curls toward the damaged side—like a bad bedhead day for plants.
Tiny holes in the spear tips
Young cutworms often start with the soft tips.
They leave small round holes that might look harmless but mess with the spear’s quality, especially if it’s for market.
If you see multiple holes in one tip, it’s probably been a multi-night buffet.
Wilting spears even with good soil moisture
Sometimes cutworms don’t cut all the way through—they just chew enough to mess up the plant’s water flow.
The spear wilts fast, even though the soil is fine. It usually affects single spears, not the whole row.
Droppings around the base
Fresh cutworm poop (yes, the fancy term is “frass”) looks like small dark pellets on the soil near damaged plants.
If you see this along with other symptoms, you’ve got proof they’re active.
Secondary Indicators and Associated Damage
Cutworms don’t always go straight for the clean snap.
Sometimes they leave smaller clues that are easy to miss if you’re not looking closely.
Scars and gouges on the stems
Instead of cutting all the way through, they sometimes just scrape the surface.
You’ll see shallow channels or scratches near the base of the spear—right where they first start chewing during their nighttime snack runs.
Extra debris around damaged spears
Cutworms are daytime introverts. They hide under mulch, leaves, or shallow soil when the sun’s up.
If you notice more debris building up around a damaged spear, it’s likely because that’s their hiding spot.
Random damage patterns
These pests don’t eat in order like some bugs.
One area might have several chewed-up spears while the row next to it looks fine.
It’s just their wandering, “eat here, wander there” style of feeding.
Distinguishing Cutworm Damage from Other Common Problems
Cutworm damage can look like other plant issues, but the details give them away.
Here’s how to tell the difference.
Cutworms vs diseases
- Fusarium crown rot and other fungi can make spears collapse, but it’s a slow fade, not a clean overnight cut.
- Disease damage usually comes with brown, black, or soggy spots and sometimes a musty, rotting smell.
- You’ll see several spears in the same patch go down at once, not random single ones.
- Phytophthora crown rot can also twist or bend spears like cutworms do, but you’ll notice water-soaked spots, root rot, and the whole plant looking weak—not just a damaged spear.
Cutworms vs. other pests
- Asparagus beetles leave scars on the surface instead of cutting spears off. They chew during the day, and you’ll spot the adults, larvae, and even eggs hanging out on the spears.
- Slugs leave messy, jagged holes instead of clean cuts, plus shiny slime trails on the plants and soil. Their damage shows up more in wet weather.
Seasonal Timing and Peak Activity Periods
Spring kickoff (March–May)
Cutworms hit their stride just as asparagus starts popping up in early spring.
The ones that spent winter underground wake up when soil temps hit around 50–55°F (10–13°C).
That’s usually 2–4 weeks before you see your first spears, so they’re ready and waiting when the buffet opens.
Weather that gets them moving
They’re most active during:
- Warm, humid nights—perfect snacking weather.
- After rain—moist soil brings them closer to the surface.
- Mild spring stretches—larvae grow faster and eat more.
Weather that slows them down
They lay low when:
- Cold snaps send them deeper into the soil.
- Long dry spells make them dig for moisture.
- Hot, dry nights kill their appetite.
Detection Strategies and Monitoring Techniques
Morning checks
During peak spring growth, make a habit of checking your asparagus early—between 6–8 AM.
That’s when fresh damage is easiest to see.
- Start with the edges of your bed—moths usually lay eggs there first.
- Note exactly where you find damage so you can track problem spots.
- Snap photos of the damage patterns; they’ll help you compare and catch trends later.
Night patrols
Cutworms feed at night, so if you want to see them in action, grab a flashlight after dark.
- Use a red filter so you don’t spook them.
- Check right around plants that got hit recently.
- Look for larvae on the spears or just under the soil surface.
- Record what you see—especially their size and how they’re feeding.
When to treat
Extension services suggest taking action when more than 5% of your asparagus is damaged. To confirm they’re the culprit:
- Pick a damaged spear.
- Dig about 1 inch deep in a 6-inch circle around it.
- Use a hand fork to sift through the soil and spot the larvae.
- Count them and make sure they’re actually cutworms before you start treatment.
Environmental Factors That Increase Cutworm Risk
Your gardening habits
Some everyday gardening choices can make life way too easy for cutworms:
- Thick layers of mulch? Cozy winter blankets for larvae.
- Weeds left hanging around? That’s like offering them a buffet and extra spots to lay eggs.
- Old, undecomposed plant bits? Perfect hiding spots.
- Uneven watering? Creates moist “hotels” in the soil where they love to hang out.
Your location
Even if you do everything right, your garden’s surroundings might still boost cutworm numbers:
- Close to weedy patches or uncut grass? That’s their neighborhood.
- Next to grain fields? Moths thrive there and can easily fly over.
- Soil loaded with organic matter? Great for plant health—also great for cutworms.
- Low spots that stay damp? VIP suites for larvae.
Integrated Detection and Prevention Strategies
Step 1 – cultural prevention
Cutworms love messy gardens. Don’t give them the satisfaction.
- Weed patrol – Keep weeds out of your asparagus beds and nearby areas. Weeds feed young larvae and give adult moths a spot to drop eggs.
- Clear old plant junk – Bury or break down leftover crop bits from last season. Fall tilling can flip hidden larvae onto the surface where birds and weather take care of them.
- Keep it clean – Remove piles of plant debris and extra mulch during high-risk periods. No trash, no hiding spots.
Step 2 – physical barriers
Sometimes the best defense is… well, an actual fence.
- Cardboard collars – Wrap each plant with cardboard that goes 2–3 inches into the soil and 3–4 inches above ground.
- Aluminum foil rings – Same idea, but shinier and lasts longer. Bonus: the reflection might confuse moths looking for a place to lay eggs.
- Diatomaceous earth – Sprinkle a ring of this gritty powder around plants. It scrapes up soft-bodied larvae like sandpaper.
Step 3 – biological control
Let nature do the dirty work.
- Beneficial nematodes – Tiny, worm-like assassins such as Steinernema carpocapsae go into the soil and hunt down cutworm larvae.
- Predator-friendly habitat – Keep some spots near your asparagus wild enough for ground beetles, birds, and other bug-hungry friends.
Step 4 – Chemical Control
Only when the other steps don’t cut it.
- Organic-approved – Use Bacillus thuringiensis (Bt), spinosad sprays, or horticultural oils. Bt is basically a bacteria smoothie for caterpillars—they drink it, they’re done.
- Conventional – Soil insecticides at planting, foliar sprays when you see active feeding, or bait granules near damaged plants for targeted hits.
Long-Term Management and Prevention
Rotate what you can
Asparagus sticks around for years, so you can’t exactly swap it out like you do with lettuce.
But you can rotate the annual crops in nearby beds.
Changing what’s planted next door helps break the cutworm life cycle.
If last year’s neighbor was a crop cutworms also love—like corn or cabbage—pick something they don’t care for.
Think of it as rearranging the buffet so the pests get lost.
Build strong, healthy soil
Cutworms go after weak plants first. If your asparagus is strong, it’s harder for them to take it down.
- Test your soil every couple of years so you actually know what it needs—guessing is for lottery tickets, not farming.
- Feed the soil the right nutrients based on the test.
- Add compost or other organic matter so your soil holds moisture and supports beneficial organisms.
Keep records
If you want to predict cutworm trouble before it happens, start tracking it.
- Write down when and where you see damage.
- Note the weather—cutworms tend to party harder in certain conditions.
- Keep track of which control methods you used and if they worked.
After a few seasons, you’ll see patterns.
You’ll know when they usually show up, what triggers them, and which tricks actually shut them down.
That way, you’re not reacting—you’re staying two steps ahead.
Bottom Line on Cutworms in Asparagus
Spot them early, save your crop. Cutworms slice spears clean or make them grow in weird curves—both are red flags.
Check your asparagus every morning, and sometimes at night, since these pests work the night shift.
If damage hits about 5%, act fast.
Use a mix of prevention, natural predators, and, if you must, targeted sprays.
Keep the good bugs safe and your soil healthy.
Stay alert, move quick, and you’ll keep your asparagus beds pumping out spears—and your harvest profits—year after year.
