First time growing sunflowers. Planted along fence line. The petals are falling off and have yellow blotches on leaves all over. Looks like they are dying. The stalks are leaning away from fence and with the heads getting heavier plants are falling over.
This is likely a Mosaic Virus.
This is a good picture representation of the leaf pattern with this disease.
Here are some links for you.
Practice of crop rotation and good watering practices are helpful in preventing this problem.
Though there is little to be done when plants become infected, I would still treat with Neem OIl.