White rust on mums: Symptoms and management

Mary Hausbeck
Plant Pathology

Recently, white rust on mums was detected in Michigan. This rust is classified as a Puccinia fungus and can spread rapidly in a greenhouse or nursery resulting in severe losses. It is a quarantine-significant disease in the United States and Canada. Pot mums, cut mums, and garden mums are all susceptible to white rust. The first symptoms appear as yellow spots on the upper leaf surface. On the undersides of the leaves, obvious pustules develop that first appear somewhat pinkish. In time, the pustules turn a waxy white color. Look for these pustules first on the young leaves and flower bracts. However, keep in mind that the pustules can be found on any green tissues and also flowers.

Within the white rust pustules are white rust survival spores that are called teliospores. These spores can last for eight weeks on dried leaves. However, if the diseased plants are buried under soil, the white rust spores survive for just one week. When the environment is wet or moist for three hours (optimum temperature is 63°F) a specialized spore forms and is called a basidiospore. These basidiospores cause an epidemic if the conditions are right. The basidiospores spread from plant to plant by splashing water and worker handling. If the plant surface is wet, the basidiospores can infect the plant tissue within two hours. The basidiospores can travel about half a mile via air currents when the relative humidity is high (90 percent or higher).

The best way to manage white rust is to prevent it. Purchase cuttings from reputable, well-known, commercial propagators. Scout the crop frequently. Remember that imported flowers should not be handled in or near mum-growing facilities. These imported flowers may be infected without showing symptoms of the white rust. Manage the environment whenever possible and keep the relative humidity low and the foliage dry. If white rust has been verified in a region, apply preventive fungicides. Fungicides suggested for a preventive program include: Heritage, Daconil, Cygnus, Dithane, Strike and Terraguard. Eagle is recommended for growers who are in a high risk area with favorable environmental conditions.

Remember, if you find white rust, it must be reported; it is the law. Regulatory officials will supervise eradication and treatment programs.

The Michigan Garden Plant Showcase: Wednesday, August 6

Erik Runkle
Horticulture

Don’t miss out on the annual Michigan Garden Plant Showcase Wednesday, August 6. This is your chance to observe how hundreds of garden plants perform in the landscape. Come view see side-by-side comparisons of new plant material surrounded by the beautiful gardens on the Michigan State University campus. In addition, come to learn more about the new plants, the Greenhouse MAEAP environmental assurance program, and how to identify and treat common greenhouse diseases. The program is listed below; registration and the program will be in the Plant and Soil Science building on the MSU Campus. Click here for a map to this event.

Time	Topic	Presenter
8:00 am	Registration and refreshments
8:30 – 10:00	Introduction and welcome Self-guided tours of display gardens	Dan Bulkowski, Manager of the Horticultural Demonstration Gardens
10:00 – 10:30	What’s New and Exciting In the 2008 Trials	Norm Lownds, Associate Professor and Annual Trial Gardens Coordinator
10:30 – 11:15	Environmental Assurance: the Greenhouse MAEAP Program	Josh Appleby, Michigan Dept. of Agriculture
11:15 – 12:00	How to Recognize and Treat Greenhouse Diseases	Mary Hausbeck, Professor of Plant Pathology
12:00 – 1:00	Lunch
1:00 –	Continue self-guided tours of gardens

For more information, visit the Michigan Garden Plant Showcase website. The $45 registration fee includes parking, morning refreshments, the program, trial booklet, and lunch. Register online, by phone at 517-355-5191 x 1339, or on site. This event is supported by Ball, Syngenta, and Yoder.

While you’re in the area, plan to stop by participating companies of the 2008 Michigan Garden Plant Tour. From August 4-15, each young plant producer showcases their plant specialties and product lines in their outdoor gardens. It’s a great way for wholesale and retail growers, garden center managers, and landscapers to stay abreast of the garden plant market. Participants can observe plant performance and trends under a variety of outdoor conditions, including landscaped settings and containers. The participating companies this year are:

C. Raker and Sons, Litchfield
Duwayne’s Greenhouse, Hudsonville
Four Star Greenhouse, Carleton
Mast Young Plants, Grand Rapids
Pell Greenhouses, Hudsonville
Walters Gardens, Zeeland
Zylstra Greenhouses, Kalamazoo

For more information on each site, including directions and tour highlights, visit the Michigan Garden Plant Tour website.