Lace bugs
Tingidae — Stephanitis and Corythucha spp.
Fine gray stippling on azalea and rhododendron leaves, with a scatter of shiny black tar spots underneath. The spots are the identification.
How to know it
A flat insect 3–4 mm long with wings held out like clear lace panels over the back, sitting still on the leaf underside. The nymphs are dark and spiny. You will usually find the excrement before the insect: hard, shiny, black varnish-like specks dotted across the underside of a stippled leaf.
What you'll see
- Fine white or yellow stippling over the upper leaf surface, coarser and blotchier than spider-mite damage.
- Shiny black tar spots on the leaf underside — the diagnostic sign, and nothing else in the garden leaves them.
- Cast skins stuck to the underside alongside the adults.
- Whole plants looking bleached and gray-green by August, and shedding leaves early.
- Damage far worse on plants in full sun than on the same species in shade.
Where it comes from
Eggs are inserted into the leaf tissue on the underside and sealed with a dab of that black varnish. Nymphs go through five stages on the same leaf, and there are two to four generations a season. Most species overwinter as eggs in the leaves of evergreens or in bark crevices, so the first generation appears very early in spring.
Hot, dry, sunny positions are the whole story: an azalea in full sun will be stippled and one of the same cultivar in shade beside it will be clean. Drought stress makes it worse, and so does anything that has killed the lacewings and pirate bugs.
Dealing with it
- Hose the leaf undersides hard with water every few days through the first generation; the nymphs cannot get back up.
- Spray insecticidal soap or horticultural oil on the undersides, timed at the first generation in late spring, which is when it does the most good.
- Water and mulch the plant; much of the visible decline is drought on top of the feeding.
- Leave the assassin bugs, lacewings and pirate bugs alone — they take a real toll if allowed.
- Accept late-season stippling; the leaves are nearly done and next year growth will be clean if the spring generation is caught.
Keeping it out
- Plant azaleas, rhododendrons and pieris in the part shade they actually want rather than in an open sunny bed.
- Mulch and water so the plant is never drought-stressed in midsummer.
- Choose resistant azalea cultivars, which are listed and genuinely differ.
- Clear fallen leaves under evergreen azaleas in autumn where the eggs overwinter.
- Check the undersides in April; the first generation is small and the easiest to stop.
What it goes for
Azaleas, rhododendrons and pieris above all; also sycamore, oak, hawthorn, cotoneaster and chrysanthemum, each with its own species.
Who hunts it for you
- Assassin bugReduviidae A patient ambusher with a curved beak it drives into whatever it catches — caterpillars, beetles, bugs, and the occasional bee, so count it a generalist rather than a specialist. It will jab a careless finger too, so admire it and leave it be. Grow to recruit it: Dill,Fennel,Goldenrod,Sweet alyssum,Tansy,Yarrow
- Green lacewingChrysoperla carnea Its bristly larvae — "aphid lions" — impale aphids, mealybugs, thrips, and mite colonies, eating hundreds a week. Adults feed on nectar and pollen from small open flowers and overwinter in hollow stems left standing. Grow to recruit it: Cilantro,Cosmos,Dill,Sunflower,Yarrow
- Minute pirate bugOrius spp. A pinhead-sized true bug that is the best natural check on thrips, and happily spears aphids, mites, and insect eggs too. It needs pollen when prey is scarce, so keep something flowering nearby. Grow to recruit it: Cosmos,Fennel,French marigold,Sweet alyssum
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com