Ten pests show up in Maryland gardens every year, and they don’t all arrive at once — that’s the part that catches people off guard. From early May through August, different ones hatch, lay eggs, or move in, so the plant that looked fine last weekend can be stripped by the time you check it again. Start now: walk your yard once a week, turn over a few leaves on your squash, tomatoes, and any viburnum, and look for holes, sticky residue, or egg clusters on the undersides — Viburnum leaf beetle in Maryland is the pest gardeners deal with most often, and it leaves exactly that kind of damage, while stripped tomato foliage and dark droppings usually point to Tomato hornworm in Maryland, which growers spot later in the season, and a squash plant that suddenly wilts in the heat of the day is often the first sign of Squash vine borer in Maryland, which gardeners battle each summer. Catching it in that first week is what makes the difference.
What Maryland gardens actually deal with
These tiny black beetles chew small round holes in seedling leaves, leaving a pattern gardeners often call shotgun damage. Adults do the visible feeding, and Flea beetles in Maryland can strip spring transplants fast enough to kill them before they establish.
Spotted lanternfly
Nymphs and adults feed on sap from a wide range of woody plants and grapevines, and gardeners dealing with Spotted lanternfly in Maryland increasingly report sticky honeydew and sooty mold left behind on leaves rather than chewed leaves. Egg masses, a gray putty-like smear on bark or flat surfaces, are the stage most worth scraping off before they hatch.
Colorado potato beetle
Both adults and the humpbacked orange larvae feed on potato, eggplant, and tomato foliage, and a heavy infestation can defoliate a potato row in days. The larvae, not the adults, usually do the worst of the damage because they feed in numbers right as plants are setting tubers.
Harlequin bug
This one targets brassicas: cabbage, kale, broccoli, collards. It pierces leaves to feed on sap, leaving pale blotchy stipple marks that turn brown and papery rather than clean chewed holes.
Squash bug
Squash bugs suck sap from squash and pumpkin leaves, causing them to wilt, yellow, and eventually turn crisp and black at the edges. Eggs laid on the underside of leaves are one of the easiest early signs to catch before nymphs disperse.
Squash vine borer
The moth lays eggs at the base of squash stems, and the larva tunnels inside, hollowing out the stem from within. A plant that wilts suddenly despite moist soil, with sawdust-like frass at the base, almost always has a borer inside rather than a watering problem.
Brown marmorated stink bug
Adults and nymphs feed on a wide range of fruits, vegetables, and ornamentals, leaving dimpled or discolored patches on fruit skin. In fall, adults move indoors to overwinter, which is often the first time a gardener actually notices them.
Viburnum leaf beetle
Larvae skeletonize viburnum leaves early in the season, leaving a lacy network of veins behind. Adults reappear later and chew irregular holes, so a viburnum can take two separate rounds of damage from the same pest in one year.
Tomato and tobacco hornworm
These caterpillars strip tomato and pepper foliage fast and can eat green fruit too. They’re large enough to hand pick once spotted, but their green color and vertical posture make them easy to miss until the damage is already extensive.
Box tree moth
First detected in Maryland in July 2025 according to UMD Extension, this newer arrival’s caterpillars feed inside boxwood shrubs, leaving webbing, green frass, and hollowed-out patches of foliage. Anyone growing boxwood in the state should check plants regularly since this pest is still being actively tracked.
Telling damage apart
The shape of the damage tells you more than the pest ever will if you can’t catch it in the act. Chewed leaf edges with ragged, ripped margins point to a chewing insect like a hornworm or beetle larva. Fine stippling, a pale speckled look across the leaf surface, usually means something is piercing and sucking sap rather than biting through tissue, which points toward stink bugs, harlequin bugs, or spider mites. Small round or irregular holes scattered across a leaf, without much other stress on the plant, are the classic sign of flea beetles or adult beetles feeding at night.
Wilting and sticky residue
Wilting is where people jump to conclusions fastest, and it’s worth slowing down. A plant that wilts evenly across the whole canopy, recovers overnight, and shows dry soil is almost always a watering problem, not a pest. A plant that wilts in just one stem or branch while the rest looks fine, especially in squash, is far more likely to be squash vine borer damage, and you should check the base of the stem for a small entry hole and frass before blaming drought. Sticky residue on leaves or the ground underneath a plant, sometimes followed by a black sooty coating, is honeydew left by sap-feeding insects like stink bugs or aphids rather than any disease process.
| What you see | Most likely cause | What to check next |
|---|---|---|
| Ragged chewed edges or holes | Chewing insect (hornworm, beetle larva, adult beetle) | Search leaf undersides and soil surface at night |
| Pale stippled speckling | Sap-feeding insect (stink bug, harlequin bug, mites) | Look for insects on stems and leaf undersides in daylight |
| Whole-plant wilting, dry soil | Watering deficit | Check soil moisture at root depth, not just the surface |
| One stem wilting, plant otherwise green | Squash vine borer or stem-boring insect | Inspect the stem base for a hole and sawdust-like frass |
| Sticky film, sooty black coating | Sap-feeding insect leaving honeydew | Look for the insect itself on nearby stems or leaf undersides |
When each one shows up
UMD Extension ties pest activity to the calendar rather than a single fixed date, and the rhythm follows plant growth stages more than the day on a calendar. Flea beetles and cucumber beetles emerge in May, right as seedlings and transplants go into the ground, which is exactly the window when young plants are least able to shrug off feeding damage. Spotted lanternfly eggs begin hatching in May, with nymphs active through July, so the scraping window for egg masses closes earlier than most gardeners expect.
Brown marmorated stink bugs lay eggs from June through August according to UMD Extension, and adults start looking for shelter indoors as fall approaches, which is often the first sign of them a gardener notices all year. July is the busiest month across the board: Colorado potato beetle, harlequin bug, squash bug, and squash vine borer are all laying eggs at once, which means July inspections should cover potatoes, brassicas, and squash in the same walk-through rather than one crop at a time.
These figures come from observations near Baltimore, and timing shifts by a week or two in either direction across the state. Gardeners in warmer states such as Mississippi see stink bugs and squash vine borer arrive several weeks earlier in the year, as covered in our Mississippi pest guide, while colder states like Minnesota compress the same activity into a shorter, more intense window, detailed in our Minnesota pest guide. Within Maryland itself, expect activity in the mountainous western counties to lag behind the Baltimore-area timing given here.
What actually works
Prevention
Rotating crops within a family, especially squash, potatoes, and brassicas, breaks the cycle for pests that overwinter in soil near where they fed the year before. Timing transplants to skip the worst of an emergence window matters more than any spray applied afterward. Physical barriers stop a lot of damage before it starts:
- Floating row cover over young squash and brassica transplants, removed once flowering starts so pollinators can reach the blooms
- Trunk or stem wraps for squash to block vine borer moths from laying eggs at the base
- Sticky bands or tape on tree trunks to intercept climbing lanternfly nymphs
Encouraging predators helps more than most gardeners give it credit for. Parasitic wasps, lady beetles, and predatory stink bugs all reduce populations of the pests on this list without any input from the gardener beyond avoiding broad-spectrum sprays that kill them alongside the target pest.
Intervention
Hand picking works well for large, slow, visible pests: hornworms, Colorado potato beetle adults and larvae, and lanternfly nymphs on low branches. For smaller or more numerous pests, targeted insecticidal soap or horticultural oil applied directly to the insect, not as a broadcast spray, controls flea beetles, squash bugs, and stink bug nymphs with the least collateral damage to beneficial insects. Garlic spray, dish soap solutions mixed at home, and ultrasonic pest repellers do essentially nothing against any pest on this list, despite how often they get recommended online. For squash vine borer, once a larva is inside the stem, no spray reaches it. The only real fix at that point is slitting the stem carefully to remove the larva or accepting the loss and replanting.
What control costs
Hand picking costs nothing but time, and it’s the cheapest option for a home garden by a wide margin. It works best on pests you can see and reach, and it has to be repeated every few days through the peak of the season since new insects keep arriving. Barriers and row cover cost more upfront for the material itself, but that cost is spread across multiple seasons if the fabric or netting is stored and reused, and once installed it needs almost no ongoing time beyond removing it for pollination and checking for gaps.
| Method | Relative cost | Time commitment | Repeat frequency |
|---|---|---|---|
| Hand picking | Lowest (time only) | Daily to every few days | Continuous through peak season |
| Barriers & row cover | Moderate upfront, reusable | One installation, brief checks | Once per season, per crop |
| Biological controls | Low to moderate | Low once established | Builds over multiple seasons |
| Targeted sprays | Moderate, ongoing purchase | Moderate, careful application | Every 7 to 10 days during outbreaks |
Biological controls, meaning predatory and parasitic insects already present in the garden, cost little beyond avoiding the sprays that would kill them. They take longer to show results than a spray does, but the payoff compounds over several seasons as populations of lady beetles, parasitic wasps, and predatory bugs build up on their own. Sprays are the most expensive option over a full season once you count repeated purchases and the labor of reapplying after rain, and they’re also the option most likely to knock back the predators doing free work in the same bed. For most home gardens, a combination of hand picking early and barriers installed at planting time beats any spray program on cost.
Local help
UMD Extension’s Home and Garden Information Center identifies pest specimens, tracks new arrivals like the box tree moth, and posts seasonal alerts as outbreaks develop. Reach it through the UMD Extension website, and if you’re gardening elsewhere in the state, the broader set of Maryland guides covers frost dates and planting windows that pair with the pest timing above. A photo and a location are usually enough for county staff to confirm what you’re looking at.
Four Common Maryland Pests Worth Knowing by Name
Not every garden problem fits neatly into a season-by-season rundown, so it helps to look at a few pests one at a time. If you’ve noticed bugs piling up on window screens or porch siding in fall, that’s likely the brown marmorated stink bug, which pushes indoors hard from mid-September through late October and again during any warm spell in January or February. Out in the vegetable patch, once soil temperatures pass 50°F in late April or early May, watch for the Colorado potato beetle, whose overwintered adults come up hungry. Around the same time, brassica growers should be scouting for the harlequin bug, which emerges from leaf litter as soil warms in mid-to-late April and stays active until the first hard frost. And once squash and pumpkin vines start spreading in late May or early June, the squash bug moves in, building steadily to a peak in late July and August. Each of these pages breaks down exactly when the pest arrives and what actually stops it.
Common questions
Do I need to spray for stink bugs every year even if I didn’t see damage last year?
No, spray on a schedule regardless of what you see. Check for the mottled brown adults or egg masses first, and only treat if numbers are actually building on your plants.
Can I compost squash plants that had vine borer in them?
Yes, but only after the growing season ends and the plant is fully dead, since a hot, actively turned compost pile kills overwintering larvae. If your compost runs cold or slow, bag and discard affected stems instead.
Are the caterpillars on my boxwood definitely box tree moth?
Not necessarily. Since box tree moth was only confirmed in Maryland in July 2025, a green and black striped caterpillar on boxwood should be photographed and sent to UMD Extension for confirmation rather than assumed.
Why do flea beetles only show up on my seedlings and not on established plants?
Young leaves are softer and have less surface area to spread the damage across, so the same number of beetles does visibly more harm to a seedling than to a mature plant. Established plants can usually outgrow light flea beetle feeding on their own.