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Downy Mildew
(fungus - Peronospora destructor): Downy mildew is an occasional disease of onion in the Lower Rio Grande Valley of Texas. Symptoms consist of white to light green spots on leaves [Picture], which later darken. A fuzzy, gray growth is seen on the leaf surface, particularly during periods of high humidity [Picture]. Lesions enlarge and leaf tissue dies [Picture]. Lesions may resemble those caused by the purple blotch fungus. Fields should be monitored closely, particularly during prolonged cold, wet weather, when the disease is more likely to occur. Fungicides that are highly effective against downy mildew, such as Ridomil and Aliette, should be applied following the first report of downy mildew in the growing area.

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