6 Pests to Guard Against in July – Nip Them in the Bud Before They Ruin Your Garden
Pests become a major problem in July if you're not careful. Watch out for these 6 bugs and your garden will thank you.
July brings a wave of garden pests out in force. Heat and lush growth are exactly what they want, and a few of them can strip a tomato plant or hollow an iris rhizome in a matter of days. Catching them early is most of the battle.
Something shifts in the garden around July. The spring rush of aphids and slugs settles down in many gardens, and a tougher, hungrier crew takes over. Some tunnel out of sight, inside stems and rhizomes, doing their damage before you notice. Others arrive in swarms, or as a single caterpillar big enough to strip a plant overnight. Warm nights and dense foliage are just what they want, and a bed that looked spotless in June can take a beating before the trouble is obvious.
Knowing the common garden pests likely to show up this month makes them far easier to stop, since most do their worst while nobody's looking. The six here hit both edible and ornamental beds, and each has a tell — a specific kind of damage, or a spot it likes to hide — that gives it away early. Catch that, and treatment is usually simple.
6 July Pests, and How to Shut Them Down
One rule cuts across all of these: early action beats cleanup, every time. By the time the damage looks dramatic, the pest has usually moved on or multiplied. Catching the first signs is the whole game.
1. Squash Vine Borer
A squash plant thriving one day and collapsed the next almost always points to squash vine borer. The adult is a clearwing moth that looks more like a wasp, laying eggs at the base of squash and zucchini stems in early to midsummer. The larvae bore straight into the stem and hollow it from the inside until the vine can't move water — hence the sudden collapse.
Look for a small hole near the base ringed with sawdust-like frass. Prevention wins here, and a floating row cover from Amazon over the young plants keeps the moth from laying in the first place — it just has to come off once flowers open for pollination.
If a borer's already inside, sometimes you can still save the plant. Slit the stem lengthwise, dig the grub out, then mound moist soil over that spot so the vine roots again above the injury and keeps feeding itself.
2. Tomato Hornworm
For something that can reach 4 inches (10cm), the tomato hornworm is shockingly easy to miss. It's the exact green of a tomato stem, with a soft spike on its tail, and it feeds fast — a couple can defoliate a plant and start on the fruit in a day or two. The droppings give it away before the caterpillar does: dark pellets on the lower leaves, bare stems up top. Handpicking at dusk works well.
Editor Kathleen Walters’ favorite way to spot them is with a UV (black light) flashlight! They light up neon-green when you shine a black light, available from Amazon, around your tomato plants in the dusk or dark. No more hiding hornworms!
For a heavier run, the go-to spray is Bt from Amazon. It's a naturally occurring soil bacterium that affects only caterpillars, harmless to everything else. One exception: a hornworm studded with white rice-like cocoons should be left alone. Those are parasitic wasps, and they are already handling it for you!
3. Iris Borer
The worst of an iris borer's damage happens underground, out of sight, which is exactly what makes it so destructive. Eggs laid last fall hatch in spring, and by July the larvae have tunneled down the leaves into the rhizome and hollowed it out. That opens the door to bacterial soft rot, which finishes the job: a firm rhizome turns to foul-smelling mush.
Early on, watch for water-soaked streaks or ragged notches along the leaf edges. No spray reaches them once they're inside, so this one comes down to sanitation. Cut and destroy old iris foliage in fall to kill the eggs before they overwinter. Divide clumps every few years and toss any rhizome that's gone soft.
4. Phlox Bug
Tall garden phlox is a July staple, and the phlox bug times its arrival to match. The orange-and-black adults and their nymphs gather on stems and leaf undersides, piercing the tissue to drink sap. The result is a stippled, mottled look — pale flecks and yellowing that curl the leaves and warp new growth, sometimes stunting the flower heads before they open.
Since they feed in groups, a quick shake over soapy water takes out a lot at once. For a real colony, insecticidal soap from Amazon sprayed onto the undersides where they hide does the trick, though it only works on direct contact. Clearing plant debris in fall removes the eggs they leave behind for next year.
5. Japanese Beetles
The traps sold for Japanese beetles are, counterintuitively, one of the worst things you can hang in a yard. The pheromone lure pulls in far more beetles than it ever catches. The beetles are hard to miss otherwise: metallic green and copper, about half an inch (1cm) long, feeding in groups through July on roses, beans, grapes, plus many more plants. They skeletonize leaves, chewing out the soft tissue and leaving a lacy web of veins.
Hand-picking is the most effective fix (as low-tech as that sounds). Knock them into soapy water early, in the cool of morning when they're sluggish. For the long game, treating the lawn for grubs thins out next summer's crop.
6. Spider Mites
Hot, dry, dusty weather is a spider mite's ideal world, which is why they tend to explode in July. They aren't insects at all, they're tiny arachnids. Spider mites a barely visible, so what most people notice first is the damage: fine pale stippling across the leaves, then a dull bronze cast as it spreads. Webbing strung between the leaves turns up later, once they're established.
Because they aren't insects, plenty of general bug sprays do nothing to them. What works is water and oil. A hard blast from the hose knocks them loose, and neem oil from Amazon smothers the rest. Raising the humidity around the plants helps, too.
