Image Number: 1440016

Blue mold may occur on the plant anytime from seedling to harvest; however, young tissue is more susceptible than old tissue. The first evidence of blue mold in the field usually occurs on the leaves as yellow circular spots about the size of a nickel. The spots soon develop the characteristic bluish, downy fungal growth on the undersides of the leaves which is best seen in the morning when the leaf is wet. If spots develop on leaves that are expanding, a puckering of the leaf occurs. As spots age, they turn from yellow to tan or brown and often tear or drop out. If infection has occurred near or on a leaf vein, a localized systematic infection may occur. The affected vein becomes reddish-brown, and the area around the vein is yellowed and distorted. In newly set transplants, it is possible for the fungus to develop systematically, killing the main bud and resulting in stunting or death of the plant. Splitting the stalk of systematically infected plants reveals a reddish- brown discoloration in the vascular tissue beneath the epidermis. A one-sided systemically infection also occur, resulting in a deformed stalk and lodging of affected plants. During weather favorable for blue mold (cool, cloudy, and wet), the disease can develop rapidly, causing numerous leaf lesions which can result in leaf blighting and severe leaf loss. The disease may develop during hot, humid periods if cool nights exist.
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Image location:
United States


Kingdom: Chromista
Phylum: Oomycota
Class: Oomycetes
Order: Peronosporales
Family: Peronosporaceae
Genus: Peronospora
Subject: Peronospora tabacina D.B. Adam


Kingdom: Plantae
Phylum: Magnoliophyta
Class: Magnoliopsida
Subclass: Asteridae
Order: Solanales
Family: Solanaceae
Genus: Nicotiana
Subject: Nicotiana tabacum (burley type) L.
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Image uploaded:
Monday, January 1, 1990
Image last updated:
Thursday, May 19, 2011