University of Wyoming Extension documents a list of garden pests for the state, and about eight of them actually go after potato: Colorado potato beetle, potato psyllid, aphids, flea beetles, cutworms, grasshoppers, blister beetles and the garden slug. The rest belong to other crops. Timing follows the growing season, which is short here, so the first weeks after planting matter most.
Which pests attack potato in Wyoming
The University of Wyoming Extension list reads like a whole garden’s worth of trouble: aphids, blister beetles, cabbage worms, Colorado potato beetle, cutworms, flea beetles, garden slug, grasshoppers, Mexican bean beetle, potato psyllid, root maggots, sugarbeet root aphid on table beets, and tomato hornworm. It also carries a timing note about something appearing on wild hosts about mid-May. That last entry is a date, not a species, and the list does not say which pest it belongs to.
Not everything on that list eats potato, and a list that long invites wasted effort. Match each pest to its crop family before you worry about it. Here is how the list sorts out.
The ones that belong on a potato page
Colorado potato beetle is the obvious one, a leaf-chewer that has specialized in this crop. Potato psyllid and aphids feed by sucking sap, and both can carry trouble beyond the bite itself. Flea beetles chew small holes in leaves. Cutworms attack young plants at the soil line. Grasshoppers and blister beetles are generalists that chew foliage when they arrive in numbers. The garden slug rounds out the group, working on leaves and sometimes on tubers in damp ground.
The ones to set aside, and why
Cabbage worms and root maggots are pests of the cabbage family, so they belong in the broccoli and radish rows. Mexican bean beetle feeds on beans. The sugarbeet root aphid is listed by the extension specifically on table beets, which tells you where it lives. Tomato hornworm is a tomato-patch pest. Potato and tomato are close relatives, so if you ever find a big green caterpillar on potato leaves, that is a question for your county office rather than a reason to reorganize your spray plans.
The list is a reasonable length, and I would not stretch it. If a pest is not on it, this site has no basis for naming it.
When each one shows up, and what it does first
The extension list does not publish a date for each species, so the calendar below rests on the plant’s own stages and on the frost window. The NOAA NCEI Climate Normals for the Cheyenne station (USW00024018) put the last spring frost between May 7 and May 18, using the 30-70% band of 32F freeze probabilities. Cheyenne sits at roughly 6,000 feet, where the season has roughly 130 frost-free days, and frost is possible in any month at higher elevations. If you plant relative to that window, as laid out in When to Plant Potatoes in Wyoming: Counting Back From Your Last Frost, the pests arrive in roughly this order.
Cutworms come first, at or just after emergence. What you see is a seedling lying on its side, cut off at the soil line, sometimes several in a row. The damage happens at night, and the culprit is usually a curled caterpillar just under the surface nearby.
Flea beetles and slugs appear around the same early stage. Flea beetles leave a scatter of tiny round holes, like fine buckshot, and the leaf is often peppered. Slug damage is ragged, with irregular holes and a slime trail on leaves or soil, worse where the ground stays wet.
Colorado potato beetle follows as the plants leaf out. Adults chew leaf edges first. Then come clusters of small orange-yellow eggs on the underside of leaves, and then the soft, humped larvae that strip foliage down to veins. Aphids show up on the undersides of leaves and tender tips in clusters, often with sticky residue below. That mid-May note about wild hosts sits right inside the frost window of May 7 to May 18. It suggests that pests are already active on wild plants near the garden while you are still setting seed pieces.
Potato psyllid tends to show as a change in the plant rather than an insect you spot: yellowing and upward-curled leaflets at the top of the plant. Grasshoppers and blister beetles come later in the season, once foliage is full and nearby vegetation starts to dry. Grasshoppers leave large ragged bites and can strip a row from the edge inward. Blister beetles turn up in clusters on leaves.
The sequence holds as a pattern, not a schedule. A cold spring pushes everything later, and a warm one pulls it earlier. Where your garden sits relative to the Cheyenne station changes it as well.
Telling the damage apart from everything else
Half the problems that look like insects are not. Frost, hail, dry soil, and fungal disease all leave marks that get blamed on bugs. This table separates the common look-alikes and shows what settles each question. It is a guide to the signs, not a diagnosis of your patch.
| What you see | Other possible causes | What settles it |
|---|---|---|
| Seedling cut off at the soil line | Frost damage, a hoe or foot, a rotting stem | A clean cut with the top lying nearby points to chewing. A mushy, pinched stem points elsewhere. Dig gently around the base for caterpillars. |
| Tiny round holes in leaves | Hail, blowing grit, early disease spots | Look at the hole edges. Chewed holes have clean edges, and spots from disease have a discolored ring around them. |
| Yellowing that starts at the top and curls upward | Nutrient shortage, water stress | Deficiency yellowing usually starts on older, lower leaves. Upper-plant curling is worth a sample to your county office. |
| Blackened or wilted leaves after a cold night | Insect feeding, disease | Frost damage is uniform across the exposed side of the bed and appears overnight. Insects work plant by plant. |
| Wilting in the afternoon that recovers by morning | Sap-sucking insects, root damage | Check soil moisture a few inches down first. Recovery overnight points to water, not to insects. |
| Brown spots with rings on leaves | Chewing insects | Disease produces spots. Insects remove tissue. Don’t treat for insects until you have looked at the leaf underside. |
Look at the underside of the leaf before you decide anything. Eggs, larvae, aphids and slime trails all show up there long before the top surface looks bad. If the leaf is clean underneath and the pattern matches weather or watering, an insect is not the first suspect.
When the signs do not settle it, take a whole affected plant, not just a photo, to your county extension office. Staff there can identify what is on it and tell you what has actually been found in your part of the state.
What actually works here, and what is a waste of time
On a short season, a physical barrier at the right moment beats a treatment after the fact. Put barriers on at planting, not after the first holes appear. Floating row cover over the bed, sealed at the edges, keeps flea beetles and egg-laying adults off young plants during the vulnerable weeks. Paper or cardboard collars around seedling stems stop cutworms from reaching the soil-line tissue they cut. Neither costs much, and both work before the damage rather than after it.
Hand-picking sounds tedious but does real work on Colorado potato beetle in a home-scale patch. Crush the orange egg clusters and knock larvae into a bucket of soapy water when you find them. Weeding the edges of the garden before mid-May removes some of the wild hosts the extension flags at that time. Drip or morning watering keeps the surface drier and helps against slugs.
Seed matters more than most gardeners expect. Certified seed is not a detail: uncertified seed carries virus, and aphids and psyllids can spread more of it. Buy certified seed and treat it as the base of your pest plan. Choose your season class as well. Utah State University Extension and the University of Maine Cooperative Extension both publish varieties by class (early, mid-season, late). Early and mid-season types fit a window of roughly 130 frost-free days better than late ones. The choices are laid out in Potato Varieties That Suit Wyoming.
Several common habits are a waste of time:
- Treating for insects when the symptom is frost, hail, or drought, which no spray fixes.
- Spraying on a calendar rather than after identifying what is actually on the plant.
- Planting early to get ahead of pests, when a late frost can cost you the whole stand.
- Relying on rotation alone in a small garden, because a beetle can walk across the yard.
This site does not name products or doses. Which pesticides are registered for potato in Wyoming, and how to use them, is a question for University of Wyoming Extension, which knows what is currently approved in the state.
Where to check this for your own county
University of Wyoming Extension is the place to start, and each county has its own office. The list above is documented for the state, and a state-wide list is never true for every garden in it. The frost window in this article comes from a station in Cheyenne at roughly 6,000 feet. A garden in a higher, colder basin has a shorter season, and its pest calendar shifts with it. Whether a given pest is common, rare or absent in your county is not something a state-level list can tell you.
Presence varies inside the state for ordinary reasons: elevation, irrigation, nearby wild vegetation, and how cold the previous winter ran. A grasshopper outbreak in one county may not touch the next. Your county office sees what is actually turning up locally, and staff can tell you whether what you are looking at is a documented concern or a look-alike.
For the bigger picture, Growing Potatoes in Wyoming covers the full season from soil to storage. This page covers only the insects and slugs on it.
Before the next planting, call or visit your county extension office and ask what has been showing up on potato locally and what they recommend. Bring a leaf, a plant, or clear photos of both sides of the leaf. It is the fastest way to turn a state-wide list into an answer for your rows.
Common questions
Which pest is the worst for potato in Wyoming?
University of Wyoming Extension documents these pests but does not rank them on this page. Colorado potato beetle is the one most tied to the crop itself. How bad any pest is in a given year depends on your county, the weather, and how early it arrives.
Do I need to watch for cabbage worms or root maggots on potatoes?
No. Both are documented for the cabbage-family part of the garden, not for potato. If you see something unexpected on potato, take a sample to your county extension office rather than assuming.
Does certified seed keep insects away?
No. Certified seed addresses virus, which uncertified seed can carry. It does not stop beetles or slugs, so it works alongside barriers and scouting rather than replacing them.
When should I start checking the plants?
From emergence, checking the underside of leaves and the soil line. Wild hosts nearby are active by about mid-May, which falls inside the May 7 to May 18 last-frost window at the Cheyenne station. Colder, higher gardens run later.