Chrysanthemum White Rust Found in Three States

January 9, 2004 - 07:20

According to a recent report from the University of Florida,
there is an outbreak of Chrysanthemum White Rust found in New Jersey, New York
and California.

Within the last 25 years the pathogen, caused by the fungal
pathogen Puccinia horiana, has come into
the United States from infected plant material. The disease causes conspicuous
and debilitating lesions on all of the green above-ground parts of florist
chrysanthemum and some close relatives. The symptoms appear mostly on the
leaves as light yellow chlorotic spots on the upper leaf surface while
corresponding buff-white raised pustules appear eventually on the lower leaf
surface. There are only two spore stages in this rust's life cycle.

The telial stage spores are present in the large unsightly
protuberant lesions on the leaf underside. These teliospores germinate in place
under very high humidity to produce the other airborne or water-splashed spore
stage, basidiospores. These basidiospores die when they dry out, so very moist
conditions cause chrysanthemum white rust to spread. Basidiospore production
from teliospores can occur in as little as three hours after wetness, and two
hours of leaf wetness is all that is required for successful infection by
dispersed basidiospores. New telial pustules appear in about two to four weeks
after infection.

The USDA-APHIS-PPQ policy is to eradicate white rust upon
detection. Conscientious survey over several weeks, careful destruction of
infected and exposed plants when discovered, and application of appropriate
fungicides to nearby plants on a prescribed schedule can very successfully
eradicate the disease.

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