Why is my plant's new growth twisted and distorted?

Everything you can see happened earlier. A leaf is formed at the growing tip when it is a fraction of a millimetre across, and damage to it at that stage is magnified enormously as the leaf expands. That is why distortion is often found after the culprit has left, and why the useful evidence is at the shoot tip rather than on the damaged leaf.

Step by step

1. Examine the growing tip, not the distorted leaf.Bend the shoot over and look into the tightly folded new leaves at the very apex, with a lens if possible. Aphids, capsid bugs and mites all feed there and are frequently still present when the damage lower down is already old.
2. Check for aphids and stickiness.Puckered, crumpled, cupped new leaves with a shiny sticky film and often ants running up the stem is aphid damage. It is the most common answer by a wide margin, and the plant grows out of it once the colony is dealt with.
3. Look for the pinprick pattern of capsid bug.Capsids feed on the tiny developing leaf and each feeding point kills a few cells. As the leaf expands, those points become small brown-edged holes with a tattered, shot-through look and the leaf grows lopsided. Fuchsias, dahlias, hydrangeas, roses, currants and beans are the classic hosts. The bug itself is fast and green and drops the instant you touch the shoot.
4. Consider mites where the tip is stunted and rosetted.Gall mites and eriophyid mites cause tightly bunched, thickened, distorted shoot tips — big bud in blackcurrants, rosetted tips on blackberries, distorted foliage on some shrubs. Growth is stunted rather than merely crumpled, and there is nothing visible to the naked eye.
5. Rule out hormone weedkiller, which is the one that matters most.Elongated, narrow, strap-like or fern-like leaves, twisted stems, cupped growth and leaves that spiral around the stem. The tell is that it affects several unrelated plants at once, is worst on tomatoes, beans, potatoes and roses, and follows either a spraying day nearby or the use of manure, grass clippings or bought compost.
6. Rule out virus.Distortion combined with irregular mottling that varies from leaf to leaf, narrow strap leaves, ring spots and permanent stunting. The key difference from weedkiller is that virus never grows out and weedkiller usually does.
7. Rule out cold and mechanical damage.A cold night on emerging growth crumples and puckers it, and so does wind rubbing a shoot against a cane or a wall. Both affect the exposed side only and both grow out completely.
8. Look for a bud problem in fruit and roses.Distorted, blackened, sticky new growth on roses in spring is often aphids; on fruit, a distorted rosette at a shoot tip may be a gall midge. On box, tightly clustered distorted tips with webbing is box tree caterpillar.
9. Judge whether it will grow out.Aphid, capsid, cold and mechanical damage all produce normal growth once the cause is removed — the distorted leaves stay distorted, and the next flush is clean. Weedkiller improves over one or two seasons. Virus never improves. That distinction is the whole decision about whether to keep the plant.

Tips

• Cut the affected shoot tips off after dealing with the cause. It removes any remaining pests and prompts a clean regrowth, and on soft plants they regrow within a fortnight.
• Capsid bugs are almost never seen because they drop and run. Hold a light-coloured tray under the shoot and tap it sharply.
• If several different plants distorted in the same week, stop looking for a pest. Weather or chemistry affects a whole garden; a pest does not.
• Keep a note of what mulch, manure or compost went where. It is the only way to identify an aminopyralid problem after the fact.

Common mistakes

• Removing all the distorted leaves and calling it fixed — The damage is caused at the tip. Unless the cause is gone, the next flush is distorted too and you have stripped the plant twice.
• Concluding virus from distortion alone — Aphids, capsid, cold and weedkiller all distort, and all four are either treatable or self-correcting.
• Spraying for capsid after the damage appears — By then the bug has moved on. Control has to be aimed at the shoot tips as growth begins, and on a garden scale is usually not worth it at all.

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