The Bugs Show Up in July!
There's a moment, usually sometime in early July, when you notice the leaves look a little dull. Not sick exactly. Just... off. Like someone breathed on them.
A week later there's fine webbing where the leaf meets the stem, and by then you're not dealing with one problem. You're dealing with a few hundred.
July is when this happens, and it's not bad luck. Hot, dry air speeds up pest life cycles dramatically — a population that would have taken a month to become visible in April can do it in eight or nine days in July. Add in the plants you moved outside for summer, and the ones you brought home from a nursery in May, and you have the conditions for the three infestations we get asked about more than everything else combined.
The good news is that they're easy to tell apart once you know where to look. The bad news is that the treatment for one of them will do nothing for the other two, which is why so many people spray something, feel better, and find the same damage three weeks later.
So let's start with identification.
First, look in the right three places
Take the plant somewhere with good light and check, in this order:
- The undersides of the leaves, especially where the leaf joins the stem. This is where nearly everything hides.
- The top inch of soil, and the air just above it. Tap the side of the pot and watch what happens.
- The newest growth, including leaves that haven't unfurled yet. Damage to brand-new leaves tells you the problem is active right now, not something the plant already recovered from.
Most people only look at the tops of mature leaves, which is the one place the damage shows up last.
Fungus gnats: annoying, mostly harmless
What you'll see: Small dark flies, a few millimeters long, drifting up in a lazy, drunken way when you water or brush the plant. They fly badly. They end up in your coffee. You'll see them near windows and screens more than on the plant itself.
Where they live: The larvae are in the top inch or two of soil — tiny, clear-to-white, with a black head, if you scrape the surface and look closely. The adults you're swatting at are the least important part.
What's actually happening: They lay eggs in consistently damp soil and the larvae feed on organic matter and fine root hairs. On a healthy, established plant, they're a nuisance. On a seedling or a fresh cutting, that root feeding does real damage.
What to do: Stop treating the adults and go after the conditions. Let the top two inches of soil dry out fully between waterings — this alone solves most cases, because the eggs can't survive it. Water from the bottom so the surface stays dry. Yellow sticky cards will knock down the adult population and, more usefully, show you whether the numbers are actually falling. If you want to hit the larvae directly, a product containing Bacillus thuringiensis israelensis (BTI, sold as mosquito bits) steeped in your watering can is specific to them and safe around pets and people.
How long: Two to three weeks of dry-surface discipline. If they come back immediately, the plant is being overwatered, or it's in a pot with no drainage.
Spider mites: the one to take seriously
What you'll see: Before you see a mite, you'll see stippling — a faint pattern of tiny pale dots across the leaf, like it was sprayed with a very fine mist of bleach. The leaf loses its gloss and looks dusty or bronzed. Fine, silky webbing in leaf joints and along stems is a later-stage sign, and by the time it's obvious the population is enormous.
Where they live: Undersides of leaves, in dense clusters. They're roughly the size of a grain of ground pepper and they don't look like much until you get close.
The confirmation test: Hold a sheet of white paper under a leaf and tap the leaf sharply a few times. Wait ten seconds and look at the paper. Specks of dust stay put. Spider mites walk.
Spider mites aren't insects — they're arachnids, and most general-purpose bug sprays aren't formulated for them. That mismatch is why people treat repeatedly and get nowhere.
What's actually happening: They pierce individual leaf cells and drain them, which is what the stippling is. Hot, dry air is ideal for them; in July conditions a generation can complete in under a week, so a population doubles while you're deciding what to do.
What to do: Isolate the plant immediately, away from everything else — mites travel on air currents and on your sleeves. Take it to a shower or a hose and spray the undersides of every leaf hard; physically removing most of the population is the highest-value step and the one people skip. Then treat with insecticidal soap or horticultural oil, covering leaf undersides thoroughly, and repeat every five to seven days for at least three rounds. The eggs aren't affected by most treatments, so a single application just clears the way for the next hatch. Raising humidity around the plant genuinely helps, because they hate it.
A July-specific warning: Don't spray oils or soaps on a plant sitting in direct sun or in high heat. It will scorch the leaves and you'll blame the pest for damage you caused. Treat in the evening, or move the plant into shade first and let it cool down.
Thrips: the frustrating one
What you'll see: Silvery or bronze streaking and scarring on the leaf surface, often in irregular patches rather than the even stippling of mites. Alongside it, tiny black specks that look like ground pepper and don't wipe off easily — that's frass. New leaves emerge crinkled, stunted, or scarred before they've even opened.
Where they live: On new growth and leaf undersides. The adults are slender, elongated, and about the size of a comma on this page; they're fast, and they'll jump or dart sideways when disturbed. Immature thrips are pale yellow and slower.
What's actually happening: Thrips rasp the leaf surface and feed on what leaks out. The reason they're hard to get rid of isn't the adults — it's that a large part of the life cycle happens in the soil, where sprays don't reach.
What to do: Isolate first. Prune off badly damaged growth and throw it away rather than composting it. Treat the plant with insecticidal soap or a spinosad-based product, and — this is the part that gets missed — treat the soil as well, not just the foliage. Repeat every five to seven days for at least four rounds. Sticky cards help you monitor, and blue cards work better than yellow for thrips.
Set your expectations: Thrips take longer than either of the others, and a month of consistent, repeated treatment is normal. Stopping early because the leaves look better is the single most common reason they come back.
The 20-second sort
- Flying around the pot, soil always damp? Fungus gnats. Dry the soil out.
- Fine pale speckling, dull leaves, webbing in the joints? Spider mites. Isolate and start a treatment cycle today.
- Silvery scarring, black specks, deformed new leaves? Thrips. Isolate, treat the soil as well as the leaves, and commit to a month.
What matters more than the product you choose
Three things, and none of them are on a shelf.
Isolate early. The moment you suspect mites or thrips, that plant goes in another room. Most infestations we hear about started as one plant and became six because it stayed on the shelf for another week.
Quarantine anything new. Two weeks away from your collection, with a check of the leaf undersides before it joins the group. Nearly every serious outbreak arrives on a new plant — including ones from good growers, ours included. It's not a sign of a bad plant. It's just how it works.
Finish the cycle. Every treatment above assumes repetition on a schedule, because none of them kill eggs reliably. One thorough round followed by three more is worth far more than four half-hearted ones, and it's the difference between solving this in July and still fighting it in September.
Check the undersides this week. That's the whole ask.
Not sure which one you've got? Send us a photo of the leaf underside and the newest growth — those two shots are usually enough for us to tell you.
Rosemary
Good Plants, Good People.