The short answer: in this region, only two of the five insects tracked locally actually feed on beet, and their timing follows the frost-free window rather than the calendar. Grasshoppers build through the warm months and hit hardest in the driest stretch of summer. Thrips show up earlier, rasping at the youngest leaves while conditions are still cool and dusty. The other three named pests belong to other crops entirely.
Which pests attack beet in Alberta
Montana State University Extension, whose Urban IPM program documents pest activity across the northern prairie and Rocky Mountain Front region bordering Alberta, names five insects for this territory: brown marmorated stink bug, grasshoppers, miller moths, social wasps, and thrips. That is the full documented list for this area on this site, and it is not padded out with anything beyond it.
Of the five, two actually feed on beet foliage. Grasshoppers chew ragged notches out of leaf margins and, in heavy years, can strip a planting down to leaf ribs. Thrips rasp at the surface of young leaves with their mouthparts, leaving a silvery, stippled scarring that’s easy to mistake for something else entirely (more on that below).
The other three have nothing to do with a beet bed, and it’s worth saying plainly why. Brown marmorated stink bug is a piercing-sucking feeder that targets fruiting crops like tomatoes, peppers, and tree fruit; it has no particular interest in beet leaves or roots. Miller moths are the adult stage of the army cutworm, and adult moths feed on nectar during their spring migration, not on garden foliage; the larval stage can clip seedlings of various crops, but the moth itself, which is what most gardeners actually see swarming around porch lights, is not a beet pest. Social wasps are predators and scavengers, hunting other insects and raiding sugary sources; they don’t chew plant tissue at all.
Treating a beet bed for brown marmorated stink bug, miller moths, or social wasps is effort spent on insects that were never going to touch the crop. If something is damaging beet leaves in an Alberta garden, the documented candidates on this list narrow down to two, and the symptoms look different enough to tell them apart without a magnifying glass.
It’s also worth being honest about scope: this is a short list. Montana State University Extension documents these five insects for the region bordering Alberta, and Alberta-specific pest surveys aren’t part of the source used here. That’s a reason to lean on county-level confirmation, not a reason to guess at additional species.
When each one shows up, and what it does first
Timing here runs off the frost-free window, not off named months, because that window is what actually governs when beets go in the ground and when insect activity ramps up. The average last spring frost for this region lands May 21, but because frost falls later than that average in one year out of two, treat it as a midpoint of a range, never as a safe planting date. Whatever happens with beet seedlings happens some weeks after that midpoint, and the pest calendar follows the same uncertainty.
Thrips tend to show up first, while conditions are still cool and often dry and dusty. The first sign is usually on the youngest leaves near the center of the rosette: a silvery, papery stippling or a faint bronzing across the leaf surface, sometimes with tiny dark specks of insect waste visible under closer inspection. Thrips populations often build fastest in dry spells, since dust and low humidity suit them, and they tend to ease off once regular rain or irrigation resumes.
Grasshoppers arrive later and build through the warmest, driest stretch of the season. Early on, the damage looks like small notches along leaf edges, easy to overlook. As the population grows through summer, that turns into larger ragged holes, chewed leaf margins working inward, and in bad years, defoliation down to the leaf veins. Grasshopper numbers typically peak in the hottest, driest weeks, which lines up with when a beet crop is also under the most heat and moisture stress from the plant’s own physiology.
That overlap matters for diagnosis. A beet plant showing stress in the hottest part of summer could be dealing with grasshopper feeding, drought stress, or both at once, and the first job for a gardener is figuring out which one is doing the damage before reaching for any kind of control.
Telling the damage apart from everything else
Insect damage on beet gets confused with heat stress, water stress, and mechanical damage more often than it gets correctly identified on sight, and the two crop-specific failures worth naming here are not insect problems at all. Water stress in the first six weeks after seeding causes premature bolting, while heat above 85 F combined with water stress later in the season makes the root turn woody — two different failures, from two different causes, at two different points in the season.
| Symptom | Possible insect cause | What distinguishes it | Likely non-insect cause |
|---|---|---|---|
| Ragged holes, chewed leaf margins | Grasshoppers | Insects visible in daylight, feeding progresses over days | Hail or mechanical damage: torn, bruised tissue matching a storm date |
| Silvery stippling on young leaves | Thrips | Concentrated on newest growth, worse in dry, dusty stretches | Nutrient shortfall: more uniform pale mottling between veins, not localized rasping |
| Root turns tough and woody | Not insect | No feeding marks anywhere on the root surface | Heat above 85 F paired with water stress |
| Plant sends up a flower stalk early | Not insect | Central stalk elongation, no chew marks on leaves | Water stress in the first six weeks after seeding |
A root that’s tough and woody with no feeding marks anywhere on it is a heat-and-drought problem, not a pest problem — nothing on this region’s documented insect list feeds on the root itself. That distinction matters, because a gardener who blames an insect for a woody root will spend a season watching for a pest that was never there while the actual cause, inconsistent watering through hot weather, goes uncorrected.
None of this replaces an actual look at the plant. When damage doesn’t clearly match either pattern above, that’s the point to bring a sample or a clear photo to a local extension office rather than guess.
What actually works here, and what is a waste of time
On a short prairie growing season, timing does more work than any product ever will. Row cover set down at seeding, not after the first chewed leaf shows up, is what actually keeps grasshoppers and thrips off a beet bed — beets don’t rely on insect pollination for the part of the plant that’s harvested, so the cover can stay on for the entire season without costing the crop anything.
Consistent watering through the first six weeks after seeding does double duty: it prevents the early bolting that water stress triggers, and it keeps beet foliage less attractive to thrips, which tend to build up faster on stressed, dusty plants. Keeping the bed weeded also removes the tall grass and volunteer growth that grasshoppers use as a bridge into a garden from surrounding open ground.
What tends to waste time: reaching for a broad-spectrum treatment the day grasshopper damage is spotted. Grasshoppers are highly mobile, moving in from surrounding grassy areas, and a treatment on one bed rarely stops fresh arrivals from an untreated field or roadside next door. Treating for brown marmorated stink bug, miller moths, or social wasps on a beet planting is also wasted effort, since none of them feed on the crop in the first place, as covered above.
This site doesn’t name products or active ingredients, and for good reason: what’s registered for use on beet varies, and a local extension office is the only source that knows current, legal options for a specific situation. Their recommendation, tied to an actual identification, will always beat a guess made from a symptom description online.
Where to check this for your own county
The pest list used on this page comes from Montana State University Extension’s Urban IPM program, documented for the region bordering Alberta rather than for Alberta itself. That’s an important caveat: it’s the closest documented source available here, not a province-specific survey, and pest presence inside any single territory varies from garden to garden depending on nearby grassland, moisture, and what’s growing next door.
The single most useful next step is contacting a local county agricultural service board or extension office with an actual sample or photo, rather than relying on a general regional list to settle what’s happening in one specific garden. A county office can also confirm what’s legally available for use against a confirmed pest, which this page deliberately does not attempt to do.
Provincial and state-level documentation is a starting point for recognizing a pattern, not a diagnosis for any individual planting. A gardener noticing repeated grasshopper or thrips damage across several seasons has good reason to flag it with a local office, since that kind of local, repeated pattern is exactly what county-level extension staff track over time.
Common questions
Do grasshoppers actually eat beet roots or just the leaves?
Grasshoppers feed on foliage, chewing leaf margins and, in heavy infestations, defoliating plants down to the veins. Nothing on this region’s documented pest list feeds on the beet root itself.
Why does bolting happen if I’m watering my beets? Isn’t that supposed to fix things?
Bolting is triggered by water stress specifically in the first six weeks after seeding. Watering consistently later in the season won’t undo an early dry spell that already pushed the plant toward flowering; the timing of the stress matters more than the total amount of water applied.
Should I worry about brown marmorated stink bug on my beets?
It’s documented for the region bordering Alberta, but it targets fruiting crops like tomatoes and tree fruit, not leafy or root vegetables like beet. It’s not a beet pest to watch for on this crop.
When is the safest time to set out row cover on beet seedlings?
Right at seeding, before either thrips or grasshoppers have a chance to find the bed. Because the average last spring frost falls later than its own midpoint in half of all years, cover placed early also buys some protection against a late frost, on top of keeping insects off.