Basil Downy Mildew Confirmed in Delaware

Nancy Gregory, Plant Diagnostician;

Basil downy mildew caused by the oomycete pathogen Peronospora belbahrii has been confirmed in Sussex County. It is very specific to basil. Symptoms on affected plants include yellowing on the top leaf surface in between the veins. Blackening of the affected leaf, especially on the margins, occurs as the disease progresses. Inconspicuous grayish dark sporulation of the downy mildew pathogen occurs on the undersides of the leaves. Basil downy mildew spores are produced in abundance and can be spread on by air currents, as well as on infected leaf material and seeds. Affected plants should be discarded. Fungicide sprays can be used in a preventative manner, but will not provide good control once the downy mildew pathogen is producing spores. Options include phosphorus acid salts such as ProPhyt or K-Phite, Actinovate, OxiDate, or Quadris, according to the label.

Symptoms of basil downy mildew on the upper side of the leaf.

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