SCREENING OF FUNGICIDES FOR THE CONTROL OF DOWNY MILDEW ON CONTAINER-GROWN CABBAGE SEEDLINGS

Eleven fungicides were screened, over three seasons, for efficacy against crucifer downy mildew, Peronospora parasitica, on cabbage seedlings grown in 24-modular polystyrene trays. Starting 10 days after emergence, seedlings were treated with weekly foliar applications of fungicide formulations. Percentage disease severity was assessed weekly using a visual rating scale; the area under the disease progress curve (AUDPC) was calculated for each treatment. A single assessment of final disease severity was an inadequate parameter for comparison of fungicide efficacy. However, AUDPC facilitated clear separation of treatments and provided an integrated measure of disease control. The mixture of cymoxanil and mancozeb was consistently found to be the most effective fungicide against crucifer downy mildew. Other fungicides that provided control included systemics (oxadixyl as a mixture with mancozeb and propamocarb) and protectants (mancozeb, chlorothalonil and cupric hydroxide). All metalaxyl-based fungicides were ineffective.