Daylily rust

About

Daylily rust is a rust fungus from Asia that reached U.S. nurseries in 2000 and spread on shipped plants. It can quickly kill daylily leaves in warm, wet weather, but cultivars vary a lot in how badly they get it.

Also called daylily rust, Daylily rust, Puccinia hemerocallidis

How to recognize it

Symptoms

Small yellow spots or streaks appear, then break open into raised bright orange to yellow powdery pustules, mostly on leaf undersides. Wiping a leaf with a white tissue leaves orange powder. Badly infected leaves yellow and die quickly, and pustules turn dark brown to black in fall.

Often confused with

Daylily leaf streak makes yellow streaks down the midvein and browning from the leaf tip down, with no orange powder.

Worse when

Wet leaves from rain, dew or sprinklers; spores can infect in as little as 5 hours of leaf wetness at about 72°F.

How it spreads

Spores blow in the wind, splash from sprinklers and ride on hands and clothes, and infected nursery plants carry it long distances; it survives winter on evergreen daylilies where winters are mild, but plants cut to the ground in cold winters usually lose it.

When

Summer and fall in warm, wet weather; new pustules form within one to two weeks of infection.

Where

Endemic in the South below about hardiness zone 7; farther north it mostly arrives on new plants.

What to do, gentlest first

Prevention works best; most sprays only protect healthy leaves and can't cure infected ones. Always read and follow the product label.

1. Grow resistant cultivars Prevent

   Cultivars that showed few symptoms in trials include 'Prairie Blue Eyes', 'Mardi Gras Parade', 'Chicago Apache', 'Buttered Popcorn', 'Frankly Scarlet' and 'Plum Perfect'. 'Stella de Oro', 'Pardon Me' and 'Gertrude Condon' were among the most susceptible.

   The rust resistance of most of the tens of thousands of named daylilies is unknown.

2. Inspect and isolate new plants Prevent

   Check leaf undersides for orange pustules before you buy, and keep new daylilies away from your bed for a few weeks to watch them. Water at the base, not overhead.

3. Cut off infected leaves and clean up By hand

   Cut and bag rusty leaves (and leaves of other daylilies in the same bed), and remove all dead foliage at the end of the season.

4. Propiconazole, myclobutanil or chlorothalonil Conventional spray

   Clemson lists these for daylily rust, sprayed every two weeks as needed and after cutting plants back. They work best before rust is widespread.

   Test on a few plants first, since some products can injure daylilies. Do not spray chlorothalonil while plants are blooming. UC IPM rates chlorothalonil high in hazard to people and to fish and other water life. Follow the label.

Plants it affects

Daylily