Floriculture Greenhouse Update

Growers of garden mums are reminded to monitor for and take precautions against Chrysanthemum white rust (Puccinia horiana), especially during cool, wet weather. Train staff to recognize symptoms and monitor plants throughout the growing season since infections can appear at any stage in crop production. Symptoms are distinctive. The first symptoms of white rust are yellow spots on upper leaf surfaces. These may become sunken and necrotic. Anyone not familiar with this disease might confuse these early symptoms with spray or insect damage.  Any sign of yellow spotting should be closely examined for further evidence of this disease. Diagnostic symptoms appear as raised pink or white waxy pustules on the undersides of the leaf. Severely infected leaves dry up and persist on the stems. Infected plants may remain symptomless for weeks, especially during hot and dry conditions. Symptoms usually appear during cooler, wet weather.

Fungicide applications may suppress disease development. Protectant fungicides include:
Azoxystrobin (Heritage), Chlorothalonil (Chlorothalonil, Daconil, Echo, Spectro 90 WDG with thiophanate-methyl), Kresoxim-methyl (Cygnus), Mancozeb (Fore, Dithane75DF, Protect DF, Pentathlon), Triadimefon (Strike), Triflumizole (Terraguard). 

Note that Myclobutanil (Eagle 20 EQ and Hoist) is an eradicant and should not be used as a preventative fungicide. Always read and follow label directions. The label is the law.

Keep susceptible varieties away from others.  Varieties that have tested positive for chrysanthemum white rust (CWR) in the past few years  include several ‘Gretchen’™ cultivars (’Bold’, ‘Bright’, ‘Flashy’, and ‘Sunny’), as well as the cultivars ‘Dark Veria’™ ‘Debonair’,™ ‘Ashley’,™ ‘Vicki’,™ ‘Okra’,™ ‘Cesaro’,™ and ‘Flamingo Pink’™ , ‘Gold Finch Yellow’ , Pink Symphony’, ‘Bold Melissa’, ‘Canelli’, ‘Heidi’, ‘Beth’, ‘Helen’, ‘Canelli’, and ‘Galatino’ that are not in the ‘Gretchen’™ series. In addition, cultivars not specified tested positive in a wide range of colors and types (some of which were grass-mum combination pots). Chrysanthemum white rust infects 12 species of chrysanthemum, including garden mums, pot mums, and Nippon daisies.

CWR is still, (at this date) a regulated pest of quarantine significance. If CWR is diagnosed, state and federal regulators remove and destroy infected plants from sites in compliance with the CWR Eradication Protocol established by the USDA APHIS-PPQ.

What to do if you see this disease:

Connecticut growers should contact state and federal regulatory agencies: USDA  APHIS-PPQ  in Wallingford (203-269-4277), and CT Agricultural Experiment Station in New Haven, Deputy State Entomologist (203-974-8474),and the Plant Diagnostic Laboratory (203-974-8601).  Regulatory personnel will supervise the eradication and treatment procedures.

Massachusetts growers should contact the Massachusetts Department of Agricultural Resources through the Pest Reporting Form or call the Pest Hotline (617-626-1779).

Additional information is available via the following links:
Photos: Chrysanthemum White Rust, 2, 3

Fact Sheet

Powerpoint presentation, with photos (presented at the Webinars listed below)

Information on CWR Eradication Protocol established by the USDA APHIS-PPQ is available on the following website. Eradication details are on page 5.
http://www.aphis.usda.gov/plant_health/plant_pest_info/cwr/downloads/cwrplan.pdf
USDA - APHIS - Plant Health, Plant Protection and Quarantine
USDA, ARS Systemic Botany and Mycology Laboratory

Webinars on CWR are being conducted (live) by Dr. Jane Trolinger, Plant Pathologist, Syngenta Flowers.   It is free, and only takes about a half-hour.  It is very informative, providing excellent photographs for recognizing the symptoms of the disease, and offers important advice on how to avoid it in your 2009 mum crop.

Choose a date and time that best fits your schedule from the list below.  Sign up by clicking on one of the times below.

Tuesday, August 18                10am Eastern Daylight Time

Tuesday, August 18                 2 pm Eastern Daylight Time

Thursday, August20_______10 am Eastern Daylight Time

Thursday, August20_______  2 pm Eastern Daylight Time

Tuesday, August25_______10 am Eastern Daylight Time

Tuesday, August25_______  2 pm Eastern Daylight Time

Sharon Douglas, Connecticut Agricultural Experiment Station
Leanne Pundt, University of Connecticut
Tina Smith, University of Massachusetts

updated 8/13/09 (Tina)