The disease overwinters in seed and diseased crop residues. Downy Mildew Downy mildew begins as small, yellow leaf spots. During periods of moist weather a mold forms on the underside of the spots. The vascular tissue discolors. The disease is worse in cool wet weather in spring and fall.
Downy mildew can predispose plants to bacterial soft rot.
The disease overwinters on seed and on crucifer weeds. Black Rot Infected seedlings turn yellow and die. Yellow, wedge shaped areas form at the leaf margins and expand inward, toward the center of the leaf, on mature plants. The affected areas later turn black and die. The vascular tissue in affected areas is black.