I noticed ants on my sunflowers earlier (now they're too tall to see 'em ) They didn't seem to do much damage, if any. Are they eating your plants? Mine are just in the veggie bed, so I'm not too worried about their looks.
Are they just ants by themselves, which won't hurt anything unless I suppose they're leafcutters, or are they ants tending herds of aphids? In which case it is really the aphids that are the problem you might want to address. (Or might not. Do the sunflowers really seem to be suffering from it?) A vigorous spray of water directed right at the aphids will knock em off and they won't generally crawl back. Repeat as needed (new aphid moms will fly in and start new herds)