Chrysanthemum White Rust Alert

OTTAWA, November 19, 2001 -- The Canadian Food Inspection Agency (CFIA) is asking home gardeners for help in eradicating a serious disease of chrysanthemums. For the first time, chrysanthemum white rust (CWR) has been found in the British Columbia commercial chrysanthemum industry and efforts are being made to trace the origins of the outbreak. The disease could have severe trade and economic implications for our commercial chrysanthemum growers.

In early October, CWR was found in several commercial chrysanthemum greenhouses. Following initial discovery of the diseased plants, the CFIA issued quarantine notices and placed destruction orders on infected plants. Traceback of movement of plants and cuttings is currently underway to reduce the possible risk of transmission.

While these greenhouses have been quarantined, a large portion of the crop had already been sold. The CFIA is asking for the public's help in eradicating the disease.

The first symptoms of white rust are whitish-yellow circular spots on the upper leaf surface. They vary in size from pinhead size to five millimeters across. As the infection develops, the spot becomes sunken and a whitish or buff-coloured pustule appears on the under surface of the leaf.

Upper leaf surface with whitish-yellow circular spots	Lower leaf surface with whitish pustles

The disease survives inside the plant, so if a chrysanthemum with CWR over-winters in the garden, it can spread the disease next fall to other chrysanthemums in your garden and surrounding gardens. It may also spread to commercial growers. It is also possible that other chrysanthemums in the garden have already been infected. Symptoms are not always obvious in the early stages of infection.

If you purchased a potted mum this fall, please do not plant it in your garden. Instead, once you have finished enjoying it, please dispose of it with your household garbage. Do not compost the plants in your backyard composter. If you planted them in your garden, as a precaution, it is recommended that you pull out the purchased chrysanthemum plus any other chrysanthemums in your garden. The disease spreads very quickly and easily from chrysanthemum to chrysanthemum.

CWR affects twelve species of chrysanthemums including potted florist mums, cut mums, and gardenmums. It does not affect people or pets, nor does it affect any plants outside of the plant groups of Chrysanthemum, Dendranthema, and Leucanthemella. It will not affect your marguerite, painted, or shasta daises.

CWR has almost a worldwide distribution with the exception of Canada and the United States. For this reason, both countries have classified CWR as a quarantinable disease. When growers have CWR they must destroy all affected plant material at their expense and are not allowed to ship any chrysanthemums until their operation is determined to be free of CWR.

Closeup of spore forming rust pustules on the lower leaf surface	Heavily infected chrysanthemum plants

Further Information:

• For more information please call CFIA's quarantine pest line at (604) 666-8884.

• Chrysanthemum White Rust Factsheet (Canadian Food Inspection Agency)

• BCMAFF Chrysanthemum White Rust Factsheet