This is downy mildew showing up on the underside of this collard leaf. While downy mildew symptoms can be seen on the top sides of the leaves, the pathogen sporulates on the underside of the leaves. This disease is most common when we have foggy mornings and periods of rainy weather. For info on managing downy mildew, look back to this post from Tony Keinath from 2021.
What Is It? Wednesday – Downy Mildew
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