Tanacetum is a genus of aromatic perennials that includes two firm favourites in UK gardens: feverfew (Tanacetum parthenium) and tansy (Tanacetum vulgare). Feverfew is the cottage garden classic, beloved for its cheerful white daisy flowers from June to September, its medicinal reputation as a migraine herb, and the gold-leaved 'Aureum' form that catches the eye in spring. Tansy is a taller UK native wildflower, spreading steadily by rhizome and producing clusters of flat yellow button flowers in late summer. Both are tough, undemanding plants that ask for very little. When their leaves start to curl, something specific is usually to blame.
Aphids: the most common cause
The single most likely reason for curling leaves on feverfew or tansy is an aphid infestation, most commonly the peach-potato aphid (Myzus persicae). These small, pale green insects colonise the soft new growth at shoot tips and the undersides of young leaves. As they feed, they distort the tissue, and the leaf curls downward to enclose the colony, making it harder to spot and harder to dislodge.
Feverfew's soft, aromatic foliage is particularly attractive to aphids in spring when colonies are establishing. The gold-leaved 'Aureum' cultivar can be more susceptible than the species type because its growth tends to be even softer. Look closely at new shoots and unfurling leaves: you will often find dense clusters of pale green insects packed tightly together. On a badly affected plant, you may also notice sticky honeydew on the leaves below the infestation, and later a sooty black mould growing on that residue.
For light infestations, a strong jet of water is enough to knock colonies off the plant. Repeat this every few days until numbers are under control. For more persistent colonies, insecticidal soap or a pyrethrin-based spray will clear them without causing lasting harm to beneficial insects if applied in the evening when pollinators are not active. Avoid broad-spectrum systemic insecticides on feverfew if you are growing it for culinary or medicinal use.
Tansy's more pungent aromatic scent does offer some natural deterrence, and established tansy plants tend to be less badly affected than feverfew. But young tansy growth in spring is not immune, especially in years when aphid populations build early.
Chrysanthemum leaf miner
The chrysanthemum leaf miner (Chromatomyia syngenesiae) is a small fly whose larvae cause a very distinctive type of damage. Rather than feeding on the leaf surface, the larvae tunnel through the internal tissue, leaving behind pale, winding lines that are visible when you hold the leaf up to the light. These serpentine mines are the giveaway: no other common pest creates this pattern.
As the larvae consume more tissue, the affected leaves develop secondary distortion and curling. The leaf may turn yellow and eventually drop. The miner is common throughout the UK on Tanacetum and other members of the Asteraceae family including chrysanthemums, marguerites, and groundsel.
There is no chemical treatment available to home gardeners that will kill the larvae inside the leaf without harming the plant. The practical approach is to remove and dispose of mined leaves as soon as you spot them. Do not put them in the compost heap, as the pupae can survive there. Bin them or burn them. Removing affected material promptly reduces the number of adults that emerge and go on to lay more eggs. The plant itself will usually recover and put out fresh growth.
Other causes worth checking
If aphids and leaf miners are ruled out, a few other conditions can cause leaf distortion or curling in Tanacetum.
Powdery mildew appears in dry spells, particularly when plants are under water stress or crowded with poor airflow. It shows up as a white or grey powdery coating on leaf surfaces, often accompanied by some leaf distortion. Improving airflow by thinning overcrowded plants and watering at soil level rather than overhead will help. Remove badly affected leaves.
Downy mildew can affect plants in cool, wet conditions, particularly in spring and autumn. The upper leaf surface develops yellow patches while the underside shows a greyish downy growth. Affected leaves curl and collapse. Again, removing affected foliage and improving airflow are the main responses. Downy mildew spreads rapidly in wet weather, so act quickly when you see the first signs.
Botrytis (grey mould) typically starts on spent flowers and can spread to leaves and stems, causing a soft brown rot with a visible grey fuzzy coating in humid conditions. Deadhead regularly to remove the entry points, and cut back affected growth to healthy tissue.
Leaf spot diseases caused by various fungal pathogens produce yellow or brown patches on leaves that can cause distortion as affected tissue dies. These are rarely serious on Tanacetum but become more common on plants that are old, overcrowded, or growing in persistently wet conditions.
Finally, consider the age of your plants. Feverfew is short-lived by nature. In its second or third year, a plant often becomes woody at the base, produces fewer flowers, and looks increasingly tatty regardless of how well you care for it. This decline makes plants more vulnerable to all the above problems. The practical answer is to treat feverfew almost as an annual: let it self-seed freely, and replace older plants with young self-sown seedlings each spring or every other year. Tansy, by contrast, spreads steadily by rhizome and persists much longer without needing replacement.
Prevention and general care
Good garden hygiene goes a long way with Tanacetum. Deadhead feverfew regularly through the flowering season to prevent excessive self-seeding in unwanted spots, and to discourage botrytis from taking hold on spent flowers. When you do want seedlings, leave a few stems to set seed in a chosen area, then thin self-sown plants to give them room to develop without competing for light and airflow.
Remove and bin any leaves showing leaf miner damage as soon as you spot them. This reduces the next generation of adults and keeps the cosmetic damage in check. Likewise, clear away fallen leaves at the end of the season to reduce overwintering sites for pest pupae and fungal spores.
Plant feverfew where it gets good sun and reasonable airflow. It is tolerant of most soils and genuinely undemanding, but cramped, airless conditions in a damp corner are an invitation to mildew and mould. Tansy is more vigorous still and can be kept in check by lifting and dividing the spreading clump every few years.
Both Tanacetum species have aromatic foliage that acts as a mild deterrent to some pests, and both are genuinely low-maintenance once established. Caught early, the problems described above are straightforward to deal with. The more likely scenario with feverfew in particular is that the plant simply needs replacing with a fresh self-sown generation.
Frequently asked questions
Why are my feverfew leaves curling downward?
Downward curling on feverfew is most often caused by aphid colonies, particularly the peach-potato aphid Myzus persicae. Check the undersides of leaves and shoot tips for dense clusters of small pale green insects. The curling is the plant's response to the aphids feeding on soft new growth. Knock them off with a jet of water or use an organic insecticidal soap.
What are the pale winding lines on my tansy leaves?
Pale, winding lines or tunnels visible through the leaf surface are the signature of the chrysanthemum leaf miner (Chromatomyia syngenesiae). The larvae of this small fly tunnel through the leaf tissue, leaving behind those characteristic serpentine mines. Remove affected leaves and dispose of them in your general waste, not the compost heap, to break the life cycle.
Should I let feverfew self-seed?
Feverfew is a prolific self-seeder, and in UK gardens this is often the most practical way to keep fresh, vigorous plants coming through. Young self-sown seedlings are healthier and less susceptible to pest problems than plants in their second or third year. Deadhead regularly if you want to control where it spreads, but let a few stems set seed to keep the next generation coming.
Can I eat or use feverfew that has had aphids on it?
Yes, once the aphids are removed and the plant has recovered, you can still harvest leaves for their traditional medicinal use. Rinse leaves well before use. Avoid harvesting leaves that show sooty mould from honeydew, as this indicates a sustained infestation that may have weakened the tissue. Fresh growth from the same plant after treatment is perfectly usable.
Why does my feverfew look tatty after a couple of years?
Feverfew is a short-lived perennial and naturally declines after two to three years. Plants become woody at the base, produce fewer flowers, and become more susceptible to disease. This is normal, not a sign of a serious problem. The straightforward fix is to replace older plants with fresh self-sown seedlings each year or every two years. Tansy behaves differently, spreading steadily by rhizome and persisting much longer.