Iris

Aphids can spread iris mosaic virus, so remove virus-streaked plants as well as the colonies; the feeding itself rarely troubles an established clump.

Dense clusters of tiny insects packed onto shoot tips, flower buds, and the undersides of young leaves. Curled, cupped, or distorted new growth that never opens properly. A sticky shine on the leaves - and on whatever sits under the plant - that later goes black with sooty mold. Tiny white cast skins left behind where a colony has been feeding. Ants running steadily up and down the stems, which is often the first thing you notice. Mottled, streaked, or misshapen leaves that do not grow out can mean a virus the aphids brought with them rather than the feeding itself.

Knock the colonies off with a hard jet of water and repeat every few days - on most plants that alone ends it. Pinch out or prune off the worst-infested tips rather than treating the whole plant. If colonies keep rebuilding, spray insecticidal soap or horticultural oil directly onto the insects, covering leaf undersides, and repeat weekly until they are gone; treat early or late in the day, and never spray a wilted or heat-stressed plant. Avoid broad-spectrum insecticides - they kill the ladybugs, lacewings, and parasitic wasps that were about to solve the problem for you, and aphid numbers usually come back worse afterward. Anything you spray must be labeled for the plant you are treating; follow that label and observe its pre-harvest interval. On anything you eat, wash leaves, heads, and buds well before use, since aphids hide down in crowns, folds, and tight growth.

Go easy on nitrogen: the soft, lush growth that heavy feeding produces is exactly what aphids breed on. Check new growth once a week through spring and early summer so you catch colonies while they are still small, and rub the first few out with your fingers. Leave flowering plants nearby and skip broad-spectrum sprays - ladybugs, lacewings, hoverflies, and parasitic wasps do most of this work for free, and they only stay if there is something for them to eat. Keep ants off the plant where you can, since they protect aphids from those predators. Water steadily so plants are not stressed, and check any new plant over before you bring it home or move it indoors, since aphids usually arrive on something else.

Aphids are small soft-bodied sap-suckers - green, black, gray, pink, or waxy white, and mostly wingless - that gather in dense colonies on the tenderest new growth: shoot tips, buds, and the undersides of young leaves. They breed extremely fast in mild weather, so a few can become hundreds inside a week. Their feeding curls and distorts soft growth, and the sticky honeydew they excrete coats everything below and turns black with sooty mold. Ants often farm and defend the colonies for that honeydew. A few aphids are normal on almost any plant and a healthy plant shrugs them off; only dense, persistent colonies do real damage, and some aphids also spread plant viruses as they feed.

Minor and cosmetic on iris - streaked petals and the occasional deformed bud in a hot, dry spell.

Silvery-white streaks and fine speckling on leaves and petals, brown discolored patches, distorted buds and blooms that fail to open properly, and tiny sliver-like insects that drop out when you shake foliage or a flower over a sheet of white paper. Worst in hot, dry spells and on drought-stressed plants.

A strong water spray dislodges light infestations, and on a plant that can take it a hard shear and clean regrowth clears them outright. For heavier pressure use insecticidal soap, neem or spinosad, aimed down into the leaf sheaths and buds where thrips actually shelter, and repeat at intervals since eggs and pupae escape a single spray. Spinosad is a registered insecticide: use only a product labeled for the crop you are treating, follow the label exactly, and observe its pre-harvest interval.

Scout early, before the damage reaches the part of the plant you care about. Start with clean planting stock, keep plants well watered since drought-stressed plants suffer worst, avoid heavy nitrogen, clear weedy hosts nearby, and hang blue or yellow sticky traps to catch the first arrivals. Reflective mulch deters them, and predatory mites, lacewings and minute pirate bugs do real work outdoors.

Tiny slender sap-sucking insects that rasp at leaves, buds and petals and drink what runs out, leaving silvery-white streaking and fine flecking, brown scorched patches, and new growth that comes out twisted or fails to open. They breed fast in hot, dry weather, shelter deep in leaf sheaths, folds and unopened buds where sprays struggle to reach, and several species also transmit plant viruses - which is often more damaging than the feeding itself.