New Hampshire gardeners contend with nine pests that UNH Cooperative Extension flags as the ones worth knowing on sight: striped cucumber beetle, Tarnished plant bug New Hampshire, squash vine borer, Japanese beetle, the Rose chafer New Hampshire, the Asiatic garden beetle in New Hampshire, flea beetles, the Lily leaf beetle in New Hampshire and the Brown marmorated stink bug in New Hampshire. Near Manchester, UNH Extension’s monitoring puts the Japanese beetle in New Hampshire emerging as adults late June into early July and peaking mid-July through August, with moths of the Squash vine borer in New Hampshire first appearing around June 20 and peak egg-laying July 10 to 15. Walk your squash and pumpkin vines every few days starting in mid-June and check the base of each stem for sawdust-like frass, the first sign a borer has already gotten in.
What New Hampshire gardens actually deal with
The real question every gardener wants answered is: what’s actually chewing on my plants, and when do I need to worry about it? The short answer is nine insects show up on a predictable schedule through the season, and most of them tip their hand before real damage sets in. So walk your beds every few days once June arrives, checking undersides of leaves, stem bases and flower buds for the early signs, whether that’s shot-holes, sawdust-like frass, or a beetle you can catch by hand before it multiplies.
Flea beetles
These are tiny, shiny black or bronze beetles barely a tenth of an inch long that jump like fleas the moment you brush a leaf. Adults chew small, round shot-holes across eggplant, radish and brassica seedlings, and a bad infestation of Flea beetles in New Hampshire can skeletonize a young plant before it gets a real start. Damage is worst on seedlings and transplants, before plants have grown past the most vulnerable stage, according to UNH Extension. Floating row cover kept on until plants toughen up is the most reliable fix.
Striped cucumber beetle
The Striped cucumber beetle in New Hampshire is about a fifth of an inch long, yellow with three black stripes running down its back and a black head, this beetle shows up as soon as cucumber, squash and melon seedlings break ground. It chews holes in leaves and stems, but the bigger problem is what it carries: bacterial wilt, which can take down a whole vine after the beetle feeds. Handpicking and row cover through early flowering keep numbers down.
Lily leaf beetle
Adults are a bright, glossy scarlet red with black legs, head and antennae, about three-eighths of an inch long and easy to spot against green lily foliage. Both the adults and the slug-like orange larvae feed on true lilies, chewing ragged holes through leaves, buds and flowers. Left alone, they can strip a lily patch to bare stems in a season. Handpicking adults in early spring, before they lay eggs, does more good than anything sprayed on later.
Rose chafer
This beetle is tan to dull yellowish-brown, about half an inch long, with noticeably long, spiny legs and a slender body. UNH Extension’s monitoring near Manchester puts its appearance at mid-to-late June, and adults feed in clusters on rose petals and foliage, skeletonizing leaves and shredding flowers. It favors light, sandy soil, so gardens on that kind of ground tend to see it worse. Handpicking into a jar of soapy water works, since sprays rarely keep pace with a fresh wave of beetles.
Tarnished plant bug
A small, mottled brown-and-bronze bug about a quarter inch long, with a flattened oval body and a pale triangular mark on its back. It feeds by piercing buds, fruit and shoot tips, which causes distorted growth, dimpled fruit and blasted flower buds rather than obvious chewing. Strawberries and stone fruit show the damage most clearly. Keeping garden edges mowed and weed-free removes the cover this bug relies on between crops.
Squash vine borer
The adult is a day-flying moth with an orange-and-black body that looks more like a wasp than a moth, but it’s the larva, a cream-white caterpillar with a brown head, that does the damage from inside squash and pumpkin stems. UNH Extension’s monitoring near Manchester puts the first moths at around June 20, with egg-laying peaking July 10 to 15 and one generation per year. Sawdust-like frass at the base of a wilting vine means a borer already got inside. Once it’s in the stem, cutting it out is the only fix.
Japanese beetle
Adults are about half an inch long with a metallic green head and thorax and coppery-bronze wing covers, plus small tufts of white hair along the edges of the abdomen. UNH Extension’s data near Manchester has adults emerging late June into early July and staying most active from mid-July through August, feeding in groups on roses, beans, grapes and linden leaves until only the veins are left. Grubs feed on turf roots earlier in the season, so a lawn heavy with grubs can mean a heavier beetle year to follow. Traps often pull in more beetles than they catch.
Asiatic garden beetle
A small, chunky, cinnamon to dull reddish-brown beetle about a third of an inch long, active at night and rarely seen in daylight unless you go looking with a flashlight. Adults chew ragged holes in annuals, perennials and vegetable leaves after dark, and can be mistaken for slug damage until you find the beetle itself. Larvae feed on grass and garden roots in the soil. Because it’s nocturnal, an evening check with a flashlight is the only reliable way to confirm it.
Brown marmorated stink bug
This bug has a shield-shaped, mottled brown body about three-quarters of an inch long, with distinctive light bands on its antennae and legs. It feeds on a wide range of fruits and vegetables, leaving discolored, pitted patches where it pierces the skin, and adults become a fall nuisance as they look for places to overwinter, including inside houses. Damage often shows up well before you spot the bug responsible.
Telling damage apart
Chewed leaf edges with ragged or scalloped bites almost always point to a beetle or caterpillar working from the outside in. Small, round shot-holes scattered across a leaf, rather than bites from the margin, are the signature of flea beetles and striped cucumber beetles working through soft young tissue. A skeletonized leaf, with only the veins left standing, usually means Japanese beetles or rose chafer have been feeding as a group rather than one insect passing through.
Stippling, a fine speckled bleaching of the leaf surface without any actual holes, is a different problem. It comes from insects that pierce and suck rather than chew, and it can also show up on leaves stressed by drought or sunscald. Wilting is the symptom that sends the most gardeners chasing the wrong cause. A vine that wilts overnight despite moist soil, with frass at the base of the stem, points to squash vine borer. A vine that wilts gradually over several days across the whole plant, with no frass anywhere, is more often a watering problem or a soilborne wilt disease, not an insect at all.
Sticky, shiny residue on leaves and on the patio underneath them is honeydew, left behind by sap-feeding insects such as aphids. It’s rarely produced by any of the chewing beetles listed above, so finding it usually means a different pest than the one that left the nearby holes.
Distorted, dimpled or lopsided fruit, along with blasted flower buds that never open, is typical of piercing feeders like tarnished plant bug rather than any chewing insect. The distinction that matters most before you treat anything is whether the damage is fresh and active or old and cosmetic. Chewed leaves from three weeks ago with no new damage this week don’t need a spray. A quick daily check for a few days, at the time you’d normally water, tells you whether a population is still active.
- Ragged, scalloped edges: a chewing beetle or caterpillar, check leaf undersides for the insect itself
- Small round shot-holes: flea beetles or cucumber beetles on young leaves
- Skeletonized leaves with veins intact: Japanese beetle or rose chafer feeding in groups
- Stippled, bleached patches with no holes: sap-feeding insects, or drought and sun stress
- Sudden wilting with frass at the stem base: squash vine borer
- Gradual, whole-plant wilting with no frass: watering fault or a soilborne disease
- Sticky residue on leaves or nearby surfaces: honeydew from sap feeders
When each one shows up
Pest activity in New Hampshire follows plant growth stages and soil warmth more than the calendar date. Flea beetle damage is worst in spring and early summer according to UNH Extension, right when seedlings and transplants are at their most tender and least able to outgrow a few chewed leaves. That window closes on its own as plants harden off and put on size, so a flea beetle problem on a six-week-old pepper plant is far less worrying than the same beetles on a seedling fresh out of the tray.
Early to late summer
Striped cucumber beetles appear the moment cucurbit seedlings emerge, so the highest-risk period is the two or three weeks after direct-seeding or transplanting squash, cucumbers and melons, before vines get big enough to shrug off some feeding. Rose chafer follows in mid-to-late June, per UNH Extension’s monitoring near Manchester, and tends to show up in waves that feed hard for a couple of weeks and then taper off. Squash vine borer moths start flying around June 20 near Manchester, with egg-laying peaking July 10 through 15 and only one generation per year, so a single well-timed check of stem bases in early July catches most of the damage before it spreads.
Japanese beetle adults emerge late June into early July near Manchester and stay active from mid-July through August, overlapping with rose chafer early on and running well past it. Tarnished plant bug and Asiatic garden beetle don’t have a single sharp peak the way these do. Plant bugs build through the growing season as buds and fruit become available to feed on, and Asiatic garden beetle activity tracks warm summer nights rather than a calendar date, which is why an evening flashlight check in July and August works better than a daytime scouting trip.
Brown marmorated stink bug adults are most noticeable in late summer and fall, when they move toward buildings to overwinter, though feeding damage on fruit and vegetables happens earlier in the season while they’re still out in the garden. These same species play out on very different calendars elsewhere. Gardeners covered in Garden Pests in New Jersey deal with a longer, hotter season that shifts many of these peaks earlier, and the pattern stretches further still in Garden Pests in Texas, where a much longer growing season changes the whole rhythm of when to watch for them.
Because UNH Extension’s timing comes from monitoring near Manchester, gardens in the North Country or along the coast can run a week or two earlier or later. Start scouting susceptible crops about a week before the earliest date given for a pest, rather than waiting for the calendar to catch up with your particular garden.
What actually works
Prevention beats intervention for nearly everything on this list, and it starts before you see a single beetle. Rotating cucurbits, brassicas and other susceptible crops to a different bed each year breaks up the pattern that lets cucumber beetles and flea beetles find the same plants in the same spot every spring. Timing transplants to go in a little later, once the ground has warmed and plants are past the tenderest seedling stage, shortens the damage window for flea beetles and cucumber beetles alike.
Barriers and encouraging predators
Floating row cover, put down at planting and sealed at the edges with soil or pins, keeps flea beetles, cucumber beetles and squash vine borer moths off plants during their most vulnerable stage. It has to come off once flowers open on crops that need pollinators, which is also roughly when the highest-risk window for these pests closes anyway. Leaving some flowering plants unmowed at the garden’s edge brings in parasitic wasps and predatory insects that go after beetle eggs and larvae without any spraying at all, and skipping broad-spectrum insecticide use protects those same predators.
Handpicking is the single most effective tool for the beetles on this list, including Japanese beetle, rose chafer and lily leaf beetle, because knocking them into a jar of soapy water in the cool of morning, when they’re sluggish, removes them without harming anything else in the garden. For squash vine borer, the only real fix once a larva is inside the stem is to slit the stem lengthwise, remove the caterpillar, and mound moist soil over the wound so the vine can root again above the damage.
Japanese beetle traps are worth naming as something that doesn’t help: the pheromone lure draws in beetles from well beyond your own yard, and poorly placed traps often increase damage on nearby plants rather than reducing it. Garlic and hot pepper sprays, marketed widely as organic repellents, wash off in the next rain and have little effect on any of the beetles or bugs listed here. Ultrasonic pest repellers marketed for garden use have no demonstrated effect on insects at all.
Where a spray is genuinely needed, targeted products like spinosad or insecticidal soap applied directly to the pest, in the evening after pollinators have left the flowers, do less collateral damage than a broad-spectrum insecticide applied on a fixed schedule. Timing the spray to when the pest is actually active, not to a set calendar day, is what makes it work at all.
What control costs
Handpicking costs nothing but time, and for most of the beetles on this list, a few minutes each morning during their active weeks is enough to keep numbers down. It has to be repeated regularly through the pest’s active window rather than done once, since new beetles keep arriving as long as the season favors them.
Row cover and other barriers cost more upfront, for the material itself plus hoops or stakes to hold it clear of the plants, but a well-kept piece can be reused for several seasons if it’s folded and stored dry over winter. The time cost is mostly in the initial setup and in removing it for pollination and any weeding underneath.
Biological controls, including beneficial nematodes for grubs or purchased predatory insects, tend to cost more per application than either handpicking or barriers, and their effect builds over a season or more rather than showing up immediately. They work best as a longer-term investment in a garden’s overall pest pressure rather than a fix for an active outbreak.
Sprays vary widely in cost depending on the product, but nearly all of them need repeat applications through a pest’s active window, since they kill what’s present at the time of spraying and do nothing for the next wave that arrives days later. That repeat cost, in both money and the time it takes to reapply correctly, adds up faster than gardeners expect over a full season.
| Method | Upfront cost | Time per season | Repeat frequency |
|---|---|---|---|
| Handpicking | None | Low, a few minutes daily during peaks | Daily through the active window |
| Row cover / barriers | Moderate, reusable | Low, mostly at setup and removal | Once per crop, replaced every few years |
| Biological controls | Moderate to high | Low once applied | Seasonal or annual |
| Targeted sprays | Low to moderate per application | Moderate, requires monitoring | Repeated through the active window |
For a home garden, handpicking combined with row cover is the cheapest approach by far, since both rely on time and reused material rather than repeat purchases, and together they cover most of what’s on this list without a single spray.
Local help
UNH Cooperative Extension tracks pest activity across the state and will identify a specimen or a photo of damage if you’re not sure what you’re looking at. Their county offices are the right first call before you spray anything, especially for damage that doesn’t match anything on this list cleanly. A correct identification is worth more than any product you could buy, since treatment aimed at a beetle does nothing for a disease or a watering problem that looks similar at a glance.
Two More Pests Worth Watching For
Beyond the general timeline above, a couple of specific insects deserve their own mention because they hit at very particular moments in the season. The rose chafer is one of them: this beetle shows up in New Hampshire gardens mid-to-late June, right as roses bud out and grape leaves fill in, and then it’s gone by midsummer, so knowing the window matters more than knowing the bug. Row covers and hand-picking handle it well if you catch it in that short stretch.
The other is the tarnished plant bug, which works on a longer clock. It becomes active as soil and air temperatures climb through late spring, and then it stays busy — feeding on tender shoots, buds, and fruit — all the way until cold weather finally sets in. Where the rose chafer is a brief, predictable visitor tied to one plant stage, the tarnished plant bug is a season-long nuisance across a wider range of crops, which changes how you’d plan to manage it. Check both pages for the details on what to look for and when to act.
Common questions
Why are there holes in my tomato leaves but no bugs anywhere?
Most chewing pests on this list feed at night or early morning and hide on the undersides of leaves or in the soil during the heat of the day. Check after dark with a flashlight, or first thing in the morning, before assuming the damage is from something that’s already gone.
Do Japanese beetle traps help or hurt?
They mostly hurt. The pheromone lure pulls beetles in from surrounding yards, and unless the trap is set well away from the plants you’re protecting, more beetles end up feeding nearby than would have shown up otherwise.
Is it too late to save a squash vine that’s already wilting?
It depends on how far the borer has gotten. If the frass and entry hole are near the base and only the tip is wilting, slitting the stem and removing the larva often lets the plant recover. A vine wilting along its full length usually means too much internal damage to save.
Will planting marigolds keep these pests away?
Marigolds have not been shown to reliably repel any of the beetles or bugs common in New Hampshire gardens. They’re worth growing for their own sake, but don’t count on them instead of row cover or handpicking.