Aphid Dew on Milkweed Leaf
The top half of the leaf is green with circular black dots. The bottom half of the leaf surface looks dirty with blackish strands or a fuzzy growth. Fungi growing on the aphid honeydew deposits cause this discoloration. Many of the leaves you see in the field will have much more discoloration that this leaf. Remember to clean the upper leaf surface before rating it for ozone injury.By the way, the circular black dots on this leaf are found on the veins and go through the leaf. Both are sure signs that this is not ozone injury.