MYCLOBUTANIL AS A CURATIVE AGENT FOR CHRYSANTHEMUM WHITE RUST

In response to a recent outbreak of chrysanthemum white rust, caused b y Puccinia horiana in California, research was conducted to test the f ungicide myclobutanil for its effectiveness as a foliar chemical contr ol for the disease. Myclobutanil applied 5 days after exposure of susc eptible plants to sporidial inoculum had extremely strong curative pro perties and usually prevented disease development in either inoculated plants or cuttings obtained from presymptomatic infected mother plant s. Even though lesions with pustules developed on inoculated plants wh en they were sprayed with the fungicide at 10, 15, or 20 days after sp oridial inoculation, the pathogen produced few sporidia in an otherwis e conducive environment. Myclobutanil at 100 mg a.i./liter, however, w as not highly effective for preventing infection when sprayed onto pla nts 5 days before inoculation, although it did reduce disease incidenc e. The data indicate that myclobutanil (100 mg a.i./liter) used as a d ip treatment for chrysanthemum cuttings prior to planting is suitable as a regulatory treatment for exclusion and eradication of chrysanthem um white rust.