Downy mildew can be recognized by the gray, dark spores that grow on the under sides of leaves, as the fungus grows systemically through the plant. Small yellow spots may develop on the upper sides of leaves as well. Infected leaves and branches eventually become distorted and die.
Downy mildew favors cool temperatures and high humidity, and can affect a wide range of hosts including cucurbits, crucifers, basil, flowers, and more.
Note: Downy mildew can sometimes be confused for powdery mildew or botrytis.
Yellow leaf spotting
Yellow spots on under side of a cucumber leaf
Yellow spots on upper side of cucumber leaf
Yellowing and browning of basil leaf
“Basil (Ocimum basilicum): Downy mildew, caused by Peronospora belbahrii” by Scot Nelson is licensed under CC BY 2.0
