The University of Wisconsin-Madison Division of Extension documents a long list of garden insects for the state, but only a handful of them feed on potato. The Colorado potato beetle leads that short list, with adults moving to potatoes in May. Flea beetles, potato leafhopper, aphids, cutworms, wireworms, white grubs and slugs make up the supporting cast. Timing follows your frost window, which at the Milwaukee reference station ends between April 16 and April 29, not the calendar on the wall.
Which pests attack potato in Wisconsin
The University of Wisconsin-Madison Division of Extension documents these garden pests for Wisconsin: aphids, asparagus beetle, cabbage looper, cabbage maggot, Colorado potato beetle, cucumber beetles, cutworms and common stalk borer, European corn borer and corn earworm, flea beetles, imported cabbageworm, onion maggot and seed corn maggot, potato leafhopper, slugs, squash bug, squash vine borer, tarnished plant bug and thrips, white grubs, and wireworms and sap beetles. That is a garden-wide list, not a potato list. Most of it has no business in a potato row.
Start with what does eat potato. The Colorado potato beetle is described in the extension material as the most distinctive pest of potatoes, and it is the one to expect every year. Flea beetles, potato leafhopper and aphids feed on the leaves. Cutworms, wireworms and white grubs work in or near the soil. Slugs feed at the surface and just below it, and they like the same damp conditions potatoes do.
Now the ones to set aside, and why:
- Cabbage looper, imported cabbageworm and cabbage maggot are named for the cabbage family and feed there, not on potato.
- Squash bug and squash vine borer are squash-family insects. Their feeding is tied to vines and fruit that a potato patch simply does not have.
- Cucumber beetles are listed as vectors of bacterial wilt, a disease of cucumbers and melons, so they belong to that crop.
- Onion maggot and seed corn maggot go after onions and germinating seed, which is a different job from raising tubers.
- European corn borer and corn earworm are named for corn, and I have no potato-specific documentation for them here.
- Sap beetles are drawn to ripening or damaged fruit and corn, not to potato plants.
Tarnished plant bug and thrips sit in the listing as general feeders. They turn up on many garden plants, so treat them as background noise unless a specialist points at them. Wireworms share a listing entry with sap beetles, but only the wireworm belongs on a potato page.
The takeaway: roughly eight of the documented groups are plausible on potato, and the rest are someone else’s problem. The extension service documents these insects for the state as a whole, though, and that does not tell you which ones live in your yard.
When each one shows up, and what it does first
Your frost window sets the clock. At the Milwaukee station behind the NOAA NCEI 1991-2020 Climate Normals, the last spring freeze falls between April 16 and April 29 (that is the 30-70% probability band for 32F). Everything below is counted from when your potatoes go in and come up, and the planting calendar counted back from your last frost shows how to set that date for your own yard.
Soil dwellers are already there before you plant. Wireworms and white grubs live in the ground, so the first evidence often comes late, when you dig and find tunnels or scarred skin on tubers. Cutworms are quicker to show: a seedling that was standing yesterday lies cut off at the soil line this morning. That happens in the weeks right after emergence, when stems are thin and tender.
The Colorado potato beetle arrives on a documented schedule. Adults move to potatoes in May, and the first thing you see is ragged holes chewed in the leaves, sometimes on plants only a few inches tall. Look under the leaves for clusters of orange-yellow eggs. The listing also carries an egg-laying start of the last week of June, which suggests a second wave of pressure later in the season. Check the undersides of leaves every few days from the time plants emerge in May. Catching the first adults and eggs is far easier than fighting a full generation of larvae.
Flea beetles announce themselves with tiny round holes, a shotgun pattern, mostly on young leaves. They hit hardest when plants are small, which means the first few weeks after emergence. A healthy plant can shrug off light holes; a seedling with half its leaf area gone cannot.
Potato leafhopper and aphids show up as changes in the leaf itself, not holes. Leaf edges go yellow, then brown and brittle, with leafhoppers. Aphids give you curled, distorted leaves, clusters on shoot tips and a sticky film. The extension listing I am working from gives no specific date for either, so watch from emergence onward and do not assume they hold off until midsummer.
Slugs feed whenever it stays wet. Look for irregular holes, silvery trails and damage that concentrates in low, shaded, mulched spots. Fall matters too, because tubers left in the ground are exposed longer. The first fall freeze comes late at the Lake Michigan shore, in early October for inland southern Wisconsin, and much earlier in the north. A late-dug crop up north carries less exposure than one left in the ground near the lake.
Telling the damage apart from everything else
Insects get blamed for a lot they did not do. Dry spells, hail, a garden fork and plain nutrient shortages all leave marks that resemble bug damage at a glance. The signs below narrow it down, but no table can name what is in your particular garden. That takes a sample and a local expert.
| What you see | Possible insect cause | Look-alike | What settles it |
|---|---|---|---|
| Ragged holes in leaves | Colorado potato beetle, slugs | Hail, wind whipping | Insects or slime trails on the plant; hail damage is uniform and torn across many plants at once |
| Tiny round holes in young leaves | Flea beetles | Early spray or fertilizer burn | Small beetles that jump when you touch the plant |
| Yellow, browning leaf edges | Potato leafhopper | Drought stress, nutrient shortage, disease | Small wedge-shaped insects on leaf undersides; drought browning shows across whole beds, not on scattered plants |
| Curled leaves, sticky film | Aphids | Herbicide drift, virus from uncertified seed | Clusters of soft-bodied insects on shoot tips; drift and virus leave no insects |
| Seedling cut at the soil line | Cutworms | Rabbits, damping-off disease | Clean cut with the top left lying nearby; damping-off leaves a pinched, water-soaked stem |
| Tunnels or holes in tubers | Wireworms, white grubs, slugs | Fork damage, growth cracks | Small, round, clean-edged tunnels versus a straight tear or split from a tool or uneven watering |
Before you buy anything, dig up a whole affected plant with roots and soil, and bring it or a clear photo to your county Extension office. That one step separates a bug problem from a water problem faster than any guesswork from the couch, and it keeps you from treating the wrong thing.
What actually works here, and what is a waste of time
A physical barrier, placed early, beats nearly every reaction after the fact. A floating row cover laid over the bed right after planting keeps the May-arriving beetles and flea beetles off young plants. It has to be sealed at the edges and it has to go on before the insects arrive. Laid down after you spot damage, it can trap the pests inside with your plants.
Rotation counts for more than people expect. Adult beetles emerge from the soil where potatoes grew last year, so planting in the same spot hands them a free meal on emergence. Move the patch as far from last year’s location as your garden allows. Hand-picking works on a small planting: knock adults into a bucket of soapy water and crush the egg clusters on leaf undersides during those May checks.
Cutworms respond to a simple collar around each seedling stem, pushed into the soil. Slugs respond to removing what shelters them, like heavy mulch pressed against stems or boards left down, and to watering in the morning so surfaces dry by evening. Starting with certified seed keeps virus out of the patch from day one.
On a season this short, timing does more than any product. Get plants in on schedule against your frost window, watch from emergence, and act on the first adults or eggs. Waiting until the plants are visibly stripped means the damage is already done.
What wastes your time:
- Spraying for pests on the full state list. Most of those insects never touch potato.
- Treating leaf browning with fertilizer before ruling out drought or leafhoppers.
- Applying anything before you know what the damage is. A wrong guess costs a week you do not have.
This site does not recommend pesticides. If you decide you need one, the University of Wisconsin-Madison Division of Extension is the place to learn what is registered for potato in Wisconsin and what the label allows.
Where to check this for your own county
The University of Wisconsin-Madison Division of Extension runs a county office in Wisconsin, and that office is where a state-level pest list becomes a local answer. Staff there can identify an insect from a sample or a photo, tell you what has been active nearby this season, and point you to what is legal and registered for your crop.
Presence varies inside the state. The frost figures here come from a single reference station, Milwaukee, and Lake Michigan delays the first fall freeze at the lakeshore while inland southern Wisconsin typically freezes in early October and the north far earlier. Insects follow that same geography. A pest documented across Wisconsin may be abundant near the lake, scarce in the north, and absent from your yard. A statewide list tells you what is possible, not what is on your plants.
For background, the overview of growing potatoes in Wisconsin covers the full season, and the guide to potato varieties that suit Wisconsin helps you choose by season class, whether early, mid-season or late, which affects how long tubers sit in the ground exposed to soil pests.
The next step is small. Write down the date your plants emerged and the date you first saw damage, take a photo of the leaf and the soil line, and contact your county Extension office with both dates.
Common questions
What is the main insect that eats potato plants in Wisconsin?
The Colorado potato beetle. The University of Wisconsin-Madison Division of Extension documents it as the most distinctive pest of potatoes, with adults moving to potatoes in May.
Do squash bugs or cabbage worms attack potatoes?
They are on the Wisconsin garden pest list, but they belong to squash and cabbage-family crops. They are not the first suspects for chewed potato leaves.
How can I tell insect damage from drought or disease?
Look for the insect itself, on leaf undersides and at the soil line, and check whether the damage is scattered or spread evenly across the bed. If you cannot tell, bring a whole plant or a clear photo to your county Extension office.
Does the frost date tell me when pests will arrive?
It sets your planting clock, and the pests follow your plants. At the Milwaukee reference station the last spring freeze falls between April 16 and April 29, but your own date will differ inland, at the lakeshore and in the north.