Did weedkiller damage my plants, and will they recover?

This is one of the few plant problems where the pattern across the whole garden matters more than the symptom on one plant. A pest attacks its host. A disease attacks its family. Chemistry hits whatever was in the way, which is why several unrelated plants going strange in the same week is the strongest possible signal.

Safety

Step by step

1. Look at how many different plants are affected.One plant, or one family, points at pest or disease. Tomatoes, beans, roses, potatoes and a clematis all distorting in the same fortnight points at chemistry. That single observation is the most diagnostic thing available.
2. Recognise the hormone weedkiller pattern.Leaves narrow and strap-like or fern-like, stems twisted and spiralled, growth cupped and elongated, leaf veins parallel rather than branching, and tomato leaves rolled tightly downwards. Tomatoes are the most sensitive indicator plant there is.
3. Recognise the contact and glyphosate drift pattern.Yellowing or white bleaching, often along leaf margins or in bands, worst on the side of the plant facing the sprayed area, sometimes with completely bleached shoot tips. Growth stops on the affected shoots. On grass it shows as a bleached stripe with a hard edge.
4. Establish the route.There are only three. Spray drift from your garden, a neighbour's, a farm or a contractor treating a path or a railway. Contaminated organic matter — manure, grass clippings, hay, straw or bought compost carrying aminopyralid or a similar herbicide from a treated pasture. Or a contaminated watering can or sprayer used previously for weedkiller.
5. Check what you mulched or fed with.Aminopyralid-type residues pass through animals and survive composting, so manure from a treated pasture damages tomatoes, beans, potatoes and dahlias grown in it a year later. If the damage is worst where the manure went and absent elsewhere, that is your answer.
6. Test the soil with a bean.The standard home test: fill pots with the suspect soil or compost and with a known-clean compost, sow broad beans or peas in both, and grow them side by side on a windowsill. If the ones in the suspect medium come up twisted and fern-like and the controls are normal, the medium is contaminated.
7. Do not feed, do not repot, and wait.There is nothing that neutralises it. Keep the plant watered normally, do not stress it further, do not add fertiliser, and let it grow. Most plants outgrow drift damage within a season, producing normal growth from the shoots above the damage.
8. Deal with contaminated soil by growing and turning.The residue breaks down through soil microbial activity, which is fastest in warm, moist, well-aerated soil with plenty of organic matter. Turn it, keep it planted with unaffected crops such as brassicas, sweetcorn, onions and grasses, and expect the sensitive crops to be usable again after one to two seasons.
9. Report a supply problem.If contaminated manure or compost came from a commercial supplier, tell them — they have a route back to the source, and it is how these problems get found. Keep the bag, the label and photographs.
10. Prevent the recurrence properly.Ask any manure supplier directly whether the pasture was treated with a hormone herbicide, use a separate labelled sprayer and watering can for weedkiller and never for anything else, do not spray in any noticeable breeze, and do not compost grass clippings from a lawn treated with weed and feed onto vegetable ground.

Tips

• Tomatoes will tell you before anything else does. Growing a couple as sentinels in a vegetable garden is a cheap early warning.
• Bindweed and brambles killed with glyphosate can pass some effect to a plant they are entwined with through root grafts and contact. Cut the weed and treat the regrowth away from ornamentals.
• A sprayer that has held weedkiller is a weedkiller sprayer for life. They are cheap; buy a second one and mark it.
• Grass clippings from a lawn treated with weed and feed should not go on a vegetable bed or into a heap destined for one.

Common mistakes

• Feeding a damaged plant to help it recover — It cannot use the nutrients while its growth regulation is disrupted, and fertiliser on a stressed plant adds a second injury.
• Digging out and replacing the plant immediately — Most recover. Give a shrub or a perennial a full season before deciding — the new growth above the damage is usually normal.
• Spreading suspect manure across the whole plot before testing it — A bean test in a pot costs a fortnight and saves a season. Test any manure of unknown origin.
• Spraying on a still-looking day next to a hedge — Very little air movement is needed to carry fine droplets several metres. Use a coarse spray setting, low pressure and a shield.

Questions people ask