Chrysanthemum White Rust

Alert for New York State

Chrysanthemum white rust (CWR) is a fungal disease of chrysanthemums caused by Puccinia horiana that  can cause severe damage, including complete crop loss due to direct effects of the disease or to quarantine  procedures.

Updated August 2023

Chrysanthemum leaf with blotches

Susceptible plants and symptoms

Pot mums, garden mums and mums grown for cut flowers are all susceptible to the disease. The  characteristic symptoms are small white to yellow spots on the upper leaf surface corresponding to pinkish to  white pustules on the lower leaf surface.

bottom of a leaf with small yellowish blotches

Identify infestations early to prevent spread

Early infestations may be hard to identify. Train workers how to identify CWR so that any outbreaks can be identified early before they spread  through the crop. The disease is very contagious within a mum planting, and can be spread to other plantings by the wind during rainy weather.

Infected plants may not show symptoms until the plants are in the proper environment.

  • Cool weather (40-73°F), high humidity (over 75%) and wet foliage for at least 5 hours promote the  development of CWR.
  • If temperatures stay above 73°F and no  rainfall is predicted, no treatment is necessary.
  • If rainfall is  predicted for a 24-hour or longer period and the temperatures  are expected to be near or below 73°F, preventative fungicide  treatment is prudent even on crops that appear healthy. 
IPM Update System
The IPM Update system is intended to help you identify your pest problems and to provide options for their management. It is currently available through email. If you would like to subscribe, please email Elizabeth Lamb.
eml38 [at] cornell.edu

Prevention is the best method of control.

  • Buy cuttings from a reliable source.
  • Inspect them when they come in and regularly thereafter for symptoms of white rust.
  • Water with drip tapes or individual emitters if  possible to avoid splashing spread via overhead irrigation.
  • Do not keep any decorative plantings of chrysanthemum on your property from year to year. 

Preventative treatments for CWR that are labeled in NY

Active IngredientsExamples of productsFungicide typeFRAC code
azoxystrobinHeritage systemic (strobilurin)11
fluoxastrobinFame SCsystemic (strobilurin)11
azoxystrobin+benzovindiflupyrMural systemic (strobilurin) + SDHI11+7
pyraclostrobin+fluxapyroxadOrkestrasystemic (strobilurin) + SDHI11+7
boscalid+pyraclostrobinPageant Intrinsic systemic (strobilurin) + SDHI7+11
fluopyram + trifloxystrobinBroadform systemic (strobilurin) + SDHI7+11
chlorothalonilDaconil contactM5
chlorothalonil+thiophanate methylSpectro contact + systemicM5+1
mancozebDithane, Protect contactM3
trifloxystrobin+triadimefonTrigo systemic (strobilurin) + DMI11+3
myclobutanilEaglesystemic (DMI)3
propiconazoleBannerMAXX systemic (DMI)3
triflumizoleTerraguard systemic (DMI)3

When using rust fungicides preventively, rotate among active ingredients and FRAC codes. Use contact (e.g. chlorothalonil and mancozeb) as  well as systemic (strobilurin and DMI or SDHI) materials within the rotation. Follow all label precautions regarding whether treatments are  recommended for plants in flower. 

For additional information on fungicides for rust management, check the  Cornell Guide for the Integrated Management of Greenhouse Crops and  Herbaceous Ornamentals (pdf).

Contact your NYS Horticulture Inspector

Because chrysanthemum white rust is a Federally regulated pest, you must contact your NYS Horticulture Inspector if you suspect your plants are infected. For contact information for your local inspector, call the Division of Plant Industry at (518) 457-2087.

This fact sheet written by Elizabeth Lamb, Ornamental Crops Coordinator, New York State Integrated Pest  Management Program, and Margery Daughtrey, Section of Plant Pathology & Plant-Microbe Biology, Cornell  University.

portrait of Betsy Lamb
Elizabeth Lamb

Senior Extension Associate, Ornamentals IPM Coordinator

NYS Integrated Pest Management

Adjunct Assistant Professor

School of Integrative Plant Science

Horticulture Section

Elizabeth Lamb
Ornamental and greenhouse integrated pest management
Margery Daughtrey
Margery Daughtrey

Senior Extension Associate

School of Integrative Plant Science

Plant Pathology and Plant-Microbe Biology Section

Margery Daughtrey
Ornamental crop disease management
Greenhouse, nursery and floriculture crops