Daylily rust

Puccinia hemerocallidis

Bright yellow-orange pustules on daylily leaves that leave a smear on your finger. Newer to North America than the plants are, and mostly a matter of tidiness.

Fungus Disfiguring Airborne sporesSpread by contact Spreads to neighbors

What you'll see

Raised yellow-orange pustules on the underside of the leaf that rub off onto a fingertip or a tissue.
Matching yellow flecks and streaks on the upper surface directly above them.
Leaves yellowing and dying back from the tips, and a clump that looks tired by August.
Later in the season the pustules darkening to brown or black as the overwintering stage forms.
Whole cultivars badly affected next to others in the same bed showing almost nothing.

Why it happens

A rust that arrived in North America in 2000 on imported plants and spread across the country in two years. It needs living tissue and spreads on wind-blown spores and on infected plants moved between gardens. In mild-winter areas it survives on evergreen daylily foliage all year; where the foliage dies down completely, it has to be reintroduced each season.

Warm, humid weather with long leaf wetness. Southern gardens with evergreen daylilies carry it year-round; northern gardens usually get it from a newly bought plant.

Treating it

Cut the affected foliage right down to the crown and bin it; daylilies regrow readily.
Bag the leaves before carrying them across the garden.
Water at the base only, and thin the clump to get air through it.
Space the fans and divide congested clumps.
A fungicide is available and rarely worth it in a garden — cutting down does as well.

Keeping it away

Quarantine new daylilies for a few weeks and inspect the leaf undersides before planting them out.
Cut all daylily foliage to the ground in late autumn and remove it, especially in mild-winter areas.
Grow resistant cultivars, which vary enormously and are widely listed.
Keep the clumps divided, open and off the irrigation line.
Remove nearby Patrinia, the alternate host, which is uncommon but does complete the cycle.

Who gets it

Daylilies. Patrinia is the alternate host.