Classic Ozone Injury on Milkweed

Ozone damaged leaf

Check out this leaf. It has all the signs of classic ozone injury. Check for:

stipples (black dots), only found between the veins, not on them

stipples are only found on the upper leaf surface

stipples have distinct, sharp edges

no haloes or discoloration around the stipple

black or very dark in color; colors are not variable

stipple is scattered over the leaf surface not clustered in groups or in obvious shapes, such as circles