I saw ants on my sunflower leaves, too; but when I looked closely, I thought they were eating or attending to an aphid type insect. Didn't notice much actual leaf damage, as we're having such dry conditions and heat here that I assumed the occasional yellow and wilt was due to that. I know aphids will suck leaf stems ,tho. I just thought the ants were not the problem.

Ants are doubly damaging where aphids are concerned. Ant farmers not only cary aphids and put them on plants, they also drive away the predators to protect them. Usually the ants are coming from a nest that is not right under the plant. I've found that spraying just around the base of the plant with Neem oil interrupts their trails. They don't seem to like to cross Neem although it doesn't kill them.

Hard to tell from this altitude and the lens Vaseline factor. Are those tiny yellow flowers? If so I would suggest it might be horse herb. That can be tough to get rid of or easy depending on your lawn type. Where do you live? What kind of grass do you have? Can you be more specific about the brand and name of the 2-4,d product you used? They're not all the same. Furthermore if you have St Augustine, you may have killed the grass with that spray.

These are photos of a Better Boy plant in SF Bay Area of California. There are pin holes in the stems of a couple of my plants. What are they? Are they hurting the plant? What can I do to get rid of the host?