Wyoming’s growing season is short and its air is dry, and the pest list that shows up in home gardens here reflects that. The University of Wyoming Extension’s MP-24 guide to home vegetable garden pests names the same recurring set year after year, starting with Aphids in Wyoming and continuing with potato psyllid, sugarbeet root aphid, blister beetles, cabbage worms, Colorado potato beetle in Wyoming, cutworms, Flea beetles in Wyoming, grasshoppers, Tomato hornworm in Wyoming, Root maggots in Wyoming, and garden slug, along with the Mexican bean beetle in Wyoming. Near Cheyenne, the potato psyllid turns up on wild host plants by mid-May, and that timing is a useful early-season signal for the whole state, though the extension service notes pressure varies from one county to the next. Check with your county extension office if something in your garden doesn’t match what’s described below.
What Wyoming gardens actually deal with
Cold nights well into late spring and a habit of swinging temperature hard within a single week both shape which insects thrive here. Pests that overwinter as eggs or pupae in soil, like cutworms and root maggots, get moving as soon as the top few inches thaw, often before a transplant has any real root system to spare. Dry, open range edges next to garden plots are exactly what Grasshoppers in Wyoming need to build up their numbers, which is part of why they show up as a late-summer problem in nearly every part of the state. The list below runs roughly in the order each pest tends to appear over a season.
Cutworms
Cutworms in Wyoming feed at night and hide in the soil by day, so the first sign is usually a seedling sheared off cleanly at ground level with no caterpillar in sight. Dig an inch or two into the soil right next to the damaged stem and you’ll usually find the culprit curled into a C-shape. A cardboard collar pushed into the soil around each transplant stops most damage without any spray.
Flea beetles
Flea beetles leave leaves peppered with small round shot-holes, most visible on young cabbage, radish, and eggplant seedlings. The beetle itself is easy to miss because it jumps the instant a leaf is disturbed. Floating row cover put down at transplant time keeps them off entirely, which matters because seedlings can be stunted permanently by heavy early feeding.
Root maggots
Root maggots work below ground on cabbage-family crops and onions, and the first visible symptom is a plant that wilts in the heat of the day despite moist soil. Pull one up and the roots will show tunneling and soft brown rot where the white larvae have been feeding. Delaying planting by a couple of weeks past the earliest possible date, once the adult flies have finished their spring egg-laying window, cuts damage substantially.
Aphids
Aphid colonies build fast once warm days arrive, clustering on new growth and the undersides of leaves where they’re easy to miss until leaves start curling. A sticky residue called honeydew, and the black sooty mold that grows on it, is often the first thing a gardener notices before spotting the insects themselves. A strong jet of water knocks most colonies down, and lady beetles and lacewings usually clean up what’s left if you haven’t sprayed anything broad-spectrum.
Colorado potato beetle
Both the adult beetle and its humpbacked orange larva feed on potato and eggplant foliage, and a heavy infestation can strip a plant to bare stems within a week. Eggs are laid in tight orange clusters on the leaf underside, and squashing those before they hatch is the single most effective non-chemical step. Hand-picking adults into a jar of soapy water each morning keeps small plantings under control.
Potato psyllid
The potato psyllid itself causes little direct feeding damage, but it transmits the pathogen behind psyllid yellows, which shows up as upward-curling, purpling leaves and stunted, misshapen tubers on potato and tomato. Near Cheyenne, University of Wyoming Extension notes the insect appears on wild host plants by mid-May, giving gardeners a rough marker for when to start checking leaf undersides for the flat, scale-like nymphs. There’s no cure once a plant shows symptoms, so early detection and removing infected plants is the only real management.
Cabbage worms
Cabbage worms chew large, irregular holes through cabbage, broccoli, and kale leaves, and their pale green color blends in so well that greenish frass pellets on the leaf are often the easier tell. The adult white butterfly flitting around the plants is a warning sign that eggs are already being laid. Bacillus thuringiensis (Bt) sprayed on the foliage kills the caterpillars without harming the butterflies or other pollinators.
Mexican bean beetle
Both the copper-spotted adult and its spiny yellow larva skeletonize bean leaves from the underside, leaving a lacy pattern of veins where the leaf tissue used to be. Damage often starts on a single plant and spreads outward through a row. Hand-picking, plus checking leaf undersides for the yellow egg clusters, keeps small infestations from becoming a whole-row problem.
Sugarbeet root aphid
This one hides below ground on table beet roots and rarely shows itself above the soil line, so the first sign is usually a beet that stops sizing up or wilts without an obvious cause. Pulling a suspect plant and checking the root surface for a white, waxy-coated aphid colony confirms it. Crop rotation away from beets for a season or two is the main practical response for a home garden.
Blister beetles
Blister beetles show up in clusters and can defoliate a row of beans or tomatoes within a day or two, feeding as a group rather than scattering across the garden. They’re worth handling with gloves, since the beetles release a chemical that can raise blisters on bare skin. Knocking them into a container rather than crushing them by hand avoids that problem entirely.
Grasshoppers
Grasshoppers chew ragged notches from leaf edges and, in bad years, can move through a garden fast enough to strip entire plants in a matter of days. Numbers build through summer on dry field and roadside vegetation before hoppers move into gardens looking for greener food. Floating row cover over vulnerable crops, put up before the hoppers arrive in force, is more reliable than any spray once a heavy flight is already underway.
Hornworms
Hornworms are large enough to do serious damage fast, and their green color camouflages them so well against tomato foliage that gardeners often spot the black droppings on leaves before they spot the caterpillar itself. A single hornworm can strip a branch of leaves overnight. Hand-picking works well because the caterpillar is slow-moving and easy to catch once you’ve trained your eye to see it.
Garden slug
Slugs feed at night and in damp, overcast weather, leaving irregular holes in leaves and a telltale silvery slime trail as the only daytime evidence. They favor low, shaded, moist spots, so damage often concentrates near mulch, boards, or dense ground cover. Reducing daytime hiding spots and hand-picking after dark with a flashlight controls most home-garden populations.
Telling damage apart
The shape of the damage tells you more than the insect ever will, especially since most pests are easier to spot by their feeding pattern than by catching them in the act. Chewed leaf edges with ragged, ripped margins point to a larger chewing insect like a grasshopper, hornworm, or cabbage worm, while small round shot-holes scattered evenly across a leaf usually mean flea beetles. Stippled, pale speckling without actual holes is a different signature entirely, more often the work of tiny sap-feeders or mites than of anything chewing solid tissue.
A few damage patterns are worth learning by name because they point straight to a cause:
- Sticky leaves with black sooty film: aphid honeydew, not a fungal disease on its own
- Plant wilting despite moist soil: root maggot or root rot, dig to check for larvae before assuming disease
- Seedling severed at the soil line overnight: cutworm, not damping-off
- Silvery slime trails with irregular holes: slug, active mainly after dark
- Leaves curling upward and purpling on potato or tomato: psyllid yellows, not a nutrient deficiency
Insect, disease, or watering fault
Uniform yellowing across a whole plant, especially starting from the bottom leaves and moving up evenly, more often points to a watering or nutrient problem than to any pest on this list. Disease tends to spread in blotches or rings with fuzzy or powdery texture, while insect damage almost always has a physical, mechanical edge to it, a hole, a notch, a tunnel, something you can trace back to a mouth. If you can’t find frass, eggs, slime, or the insect itself after a close look at the underside of the leaf, treat it as a watering or disease question first rather than reaching for an insecticide that won’t help.
What actually works
Prevention does more work than any spray, and it costs less over a season. Rotating nightshades, cabbage-family crops, and beans to a different bed each year breaks the life cycle of soil-dwelling pests like root maggots and sugarbeet root aphid, since many of them can’t travel far to find next year’s host. Timing a transplant a week or two later than the earliest possible date often lets a seedling miss the peak egg-laying window for cutworms and root maggot flies entirely, which is a bigger factor in survival than any single treatment applied afterward.
Physical barriers are the next most reliable tool. Floating row cover excludes flea beetles, cabbage worm adults, and grasshoppers outright as long as it’s sealed at the edges and removed before flowering crops need pollinators to reach them. Cardboard or metal collars around transplant stems stop cutworms without any chemical involved. Gardeners in wetter, more humid states like Illinois deal with a similar early-season aphid and cabbage worm pressure, but the dry Wyoming air actually slows some fungal problems that make pest damage worse elsewhere.
Encouraging predators and using targeted sprays
Lady beetles, lacewings, and parasitic wasps handle a meaningful share of aphid and cabbage worm populations on their own, provided broad-spectrum insecticides aren’t wiping them out along with the pest. Bacillus thuringiensis (Bt) is one of the few sprays worth reaching for, since it kills caterpillars like cabbage worms and hornworms while leaving bees, beetles, and other beneficial insects unharmed. Insecticidal soap does real work against soft-bodied aphids and psyllid nymphs but does nothing to a hard-shelled Colorado potato beetle or a blister beetle, so matching the tool to the pest matters more than reaching for whatever’s on the shelf.
A few widely repeated home remedies do little to nothing. Garlic or hot pepper sprays wash off in the first watering and rarely survive contact with sun. Beer traps catch some slugs but need refilling every night or two to keep working, so they’re more a labor commitment than a fix. Companion planting marigolds as a blanket repellent has not shown reliable control against any pest on this list, useful mainly as a filler plant rather than a defense.
What control costs
Hand-picking costs nothing but time, and for beetles, hornworms, and slugs it’s genuinely the cheapest option available to a home gardener, provided you’re willing to check plants every day or two through the peak weeks. Row cover and stem collars cost money upfront but get reused season after season, so the per-year cost drops fast after the first purchase. Biological controls, whether it’s Bt or simply not spraying so predator insects can build up, cost almost nothing beyond the price of the product itself and need reapplication only after rain washes it off. Broad-spectrum sprays are the most expensive option over a full season once you count repeat applications, and they carry the added cost of knocking back the very predators that would otherwise be doing free pest control.
| Method | Cost | Time per season | How often repeated |
|---|---|---|---|
| Hand-picking | Lowest, no materials | Daily checks in peak weeks | Ongoing through the infestation |
| Row cover and collars | Upfront purchase, reused for years | One setup per bed | Once per planting, reused annually |
| Biological controls (Bt, predators) | Low | Occasional spray or none at all | After rain or new hatch |
| Broad-spectrum sprays | Highest over a season | Repeated application and monitoring | Every 7 to 14 days typically |
For a small home garden, hand-picking and barriers together cover most of the pests on this list without any ongoing spray budget. Warmer states with a longer pest season, like Arkansas, often see enough generations per year that gardeners lean harder on sprays just to keep up, a tradeoff Wyoming’s short season mostly avoids.
Local help
The University of Wyoming Extension is the right first call for anything that doesn’t match the descriptions above, since county offices can identify a specimen and track whether a particular pest is running heavier than usual in your area this year. Their MP-24 guide to home vegetable garden pests is the source for the list covered on this page. Start at the University of Wyoming Extension office directory to find your county’s contact, and browse the rest of our Wyoming guides for planting timing that works alongside pest management.
Two More Pests Worth Watching For
Wyoming gardens face a couple of other troublemakers that don’t fit neatly into a single season, and each one deserves its own look. If you grow alfalfa nearby or your yard borders a hay field, keep an eye out for blister beetles, which tend to show up from late June through August after a stretch of warm, dry weather following the first alfalfa cutting. The bigger worry isn’t the beetle itself, since it barely bites, but the toxin it carries, and that page walks through when to expect them and what actually stops them. If your brassicas are the target instead, the timeline runs differently: cabbage worms arrive once transplants have had two to three weeks in warm soil rather than on any fixed date, and the University of Wyoming Extension tracks their progress through the state’s short, cool growing season. That page breaks down how to spot them early and keep them from stripping your cabbage and broccoli before harvest.
Common questions
Why do my potato leaves look purple and curled but I don’t see any bugs?
That’s the classic symptom of psyllid yellows, caused by the potato psyllid, and the insect itself is often gone or too small to spot by the time the leaf symptoms show up. Check nearby leaves for the flat, pale nymphs on the underside, and remove badly affected plants since there’s no way to reverse the damage once it appears.
Do I need to spray for grasshoppers every year?
Not necessarily. Grasshopper numbers swing a lot from year to year depending on how dry the surrounding rangeland was the previous summer, so a bad year is often followed by a lighter one. Row cover put up before hoppers move in from dry field edges is worth doing regardless of how heavy the year looks, since it costs little and works whether the flight turns out to be big or small.
Are the beetles on my beans ladybugs or Mexican bean beetles?
Look at the spot count and the plant they’re on. Mexican bean beetle is copper-yellow with sixteen black spots and feeds specifically on bean foliage, while most true ladybugs have fewer spots and are usually found eating aphids rather than leaf tissue. If you’re still unsure, your county extension office can confirm from a photo or a sample.
Will planting marigolds keep pests out of my whole garden?
No, and this is one of the more persistent garden myths. Marigolds have not shown reliable control against any of the pests common in Wyoming gardens, so treat them as a nice-looking filler plant rather than a defense strategy, and rely on row cover, rotation, and hand-picking instead.