Why Are My Echinacea Leaves Curling?

Powdery mildew

The most commonly encountered foliar disease of echinacea in UK gardens; most prevalent in hot, dry, late summer conditions. White, fine, powdery patches develop on leaf surfaces, first on lower older leaves and spreading upward; affected leaves may curl slightly and turn pale or yellowish. Most severe on plants in dry, thin, well-drained soil in hot, sunny, exposed positions where root drought stress combines with warm dry air around the leaves.

What to do

• Incorporate well-rotted garden compost into the planting hole to improve moisture retention; apply a mulch of composted bark (5 to 7 cm) in spring to maintain root moisture; water deeply during prolonged dry spells in July to September; good air circulation around plants reduces mildew severity; sulphur-based fungicide sprays are approved in the UK for powdery mildew on ornamental plants; remove and dispose of the most severely mildewed leaves.

Vine weevil

Otiorhynchus sulcatus (vine weevil) larvae cause catastrophic root damage to container echinacea. The diagnostic sign: a container echinacea suddenly wilts and collapses even when the compost is moist. Tipping out the pot reveals cream-coloured, C-shaped, legless larvae in the root zone. Adult vine weevils cut distinctive irregular notched scallops from leaf margins at night.

What to do

• For containers with active larval damage: tip the plant and compost out of the pot immediately; remove larvae by hand from the root ball and compost; replace all the compost entirely before repotting; apply entomopathogenic nematodes (Steinernema kraussei or Heterorhabditis bacteriophora) watered into moist compost in late summer (September to October) as a preventative; S. kraussei is effective when soil temperature is above approximately 5°C; nematodes are widely available from UK biological control suppliers; ensure containers have large drainage holes and do not sit in saucers of water.

Aster yellows

Caused by Candidatus Phytoplasma asteris, transmitted by leafhopper insects. Very distinctive symptoms unlike any fungal disease: flower petals replaced by small green leafy structures (phyllody); abnormal greening of flower parts (virescence); unusually bushy congested side-shoot proliferation (witches' broom); narrow pale mottled yellow-green leaves; general stunting. No cure; remove and destroy affected plants immediately.

What to do

• Remove infected plants from the garden immediately and dispose of them in general waste; do not compost infected plant material; replace with healthy specimens in a different area of the garden to reduce the risk of leafhoppers transmitting the disease to new plants; not all distorted echinacea is aster yellows: the distinctive combination of green flowers, phyllody, witches' broom, and yellowing together is the most reliable diagnostic indicator; single symptoms in isolation are not sufficient to diagnose aster yellows.

Poor drainage in heavy UK clay soils

Echinacea is native to freely draining, often dry North American prairie soils and is intolerant of persistently waterlogged, poorly draining heavy clay soil. In a very wet UK clay soil, roots develop root rot; the plant wilts, leaves turn yellow, and the plant dies back. Different from its prairie-adapted drought tolerance: it can handle dry summers but not wet, cold, anaerobic winter soil.

What to do

• On heavy UK clay soils, improve drainage by incorporating large quantities of coarse horticultural grit and well-rotted organic matter into the planting area; or grow in a raised bed where drainage is naturally better; avoid planting in low-lying wet spots or at the bottom of slopes where cold wet soil accumulates in winter; choose a slightly raised, sunny, open position that drains freely.

Frequently asked questions

Why are my echinacea leaves curling?

Echinacea leaves curl and yellow most commonly because of powdery mildew (white fine powdery patches on leaf surfaces; most severe in hot dry late summer; incorporate compost to improve root moisture retention; mulch; water deeply in dry periods July to September; good air circulation; sulphur-based fungicide approved in UK for ornamental plants), vine weevil (cream-coloured C-shaped legless larvae in container compost; sudden catastrophic wilting despite moist compost; adult vine weevil cuts irregular notched scallops from leaf margins at night; tip plant out of pot; remove larvae by hand; replace all compost; apply Steinernema kraussei nematodes in late summer; nematodes effective above approximately 5°C), aster yellows (phytoplasma transmitted by leafhoppers; very distinctive combination of green flowers phyllody witches' broom narrow pale mottled yellow-green leaves and general stunting; no cure; remove and destroy infected plants; do not compost), or poor drainage in heavy UK clay soils (native to freely draining prairie soils; intolerant of persistently waterlogged heavy clay; improve drainage with coarse grit and organic matter; or raised bed; avoid low-lying wet spots).

How do I treat vine weevil on echinacea?

Adult vine weevil damage: small (8 to 9 mm) dull greyish-black flightless beetle with curved beak and elbowed antennae; nocturnal; characteristic irregular scalloped notches cut from leaf margins; disfiguring but not usually fatal; sign to prompt investigation and treatment for larvae. Larval vine weevil damage: adult female lays hundreds of tiny cream-coloured oval eggs in container compost from May to July; eggs hatch into cream-coloured legless C-shaped grubs; feed on roots from autumn through winter; largest and most damaging October to March; catastrophic wilting and death of container echinacea even when compost is moist. Treatment: for active larval damage tip plant out of pot and remove larvae from root ball and compost by hand; replace compost entirely before repotting; biological control: entomopathogenic nematodes (Steinernema kraussei effective above approximately 5°C; Heterorhabditis bacteriophora effective above 12°C) watered into moist compost in late summer (September to October); widely available from UK biological control suppliers; apply preventatively each year in late summer for container echinacea.

What is aster yellows and can echinacea recover?

Caused by Candidatus Phytoplasma asteris, a phytoplasma (unusual cell-wall-lacking bacterial-like organism living within the phloem tissue of infected plants), not by a fungus virus or conventional bacterium. Symptoms: phyllody (flower petals transformed into small green leaf-like structures); virescence (abnormal greening of flower parts; normally coloured petals remain green); proliferation and witches' broom (unusual number of small congested bushy side shoots); yellowing and distortion of leaves (unusually narrow pale or mottled yellow-green rather than normal dark green); general stunting. Transmission: transmitted by leafhopper insects (Macrosteles fascifrons and related species); cannot be spread by pruning tools or plant contact without a leafhopper vector; once a plant is infected the phytoplasma spreads through the plant's phloem. Recovery: no cure or treatment; infected plants cannot recover; remove and destroy infected plants immediately; do not compost; replace with healthy specimens in a different garden area. Diagnosis: the distinctive combination of green flowers phyllody witches' broom and yellowing together is the most reliable diagnostic indicator; single symptoms in isolation are not sufficient.

How do I grow echinacea in UK gardens?

Full sun: best in a full sun or very light dappled-shade position; in significant shade flowering is reduced stems become drawn and floppy and plants are more susceptible to disease. Well-drained but reasonably moisture-retentive soil: good drainage prevents root rot in wet UK winters; unlike intensely Mediterranean herbs echinacea does not need bone-dry thin soil; a well-drained but reasonably moisture-retentive humus-enriched soil gives the best combination of good drainage and adequate summer moisture; incorporate well-rotted garden compost into the planting hole on free-draining soils to improve moisture retention; add coarse grit on very heavy clay soils to improve drainage. In-ground plants: once well-established remarkably drought-tolerant and long-lived; divide every 3 to 4 years to refresh vigour; much less susceptible to vine weevil damage than container plants. Containers: particular vigilance for vine weevil larvae; apply nematode biological control in late summer preventatively; ensure large drainage holes; do not sit in saucers of water.