We do not (and cannot) recommend a treatment without knowing what is causing the damage; not all active ingredients are effective against all potential pests. Potential culprits for chewed leaves include deer, rabbits, grasshoppers, katydids, tree crickets, caterpillars, sawfly larvae, beetles, earwigs, and slugs/snails. Aphids don't chew foliage, though there are some reddish aphids that can suck sap on sunflower stems (though they wouldn't need treatment).

You can keep an eye on the plants and check the leaf undersides periodically as well as inspect them with a flashlight after dark, since some insects and slugs/snails feed only at night. If you find something that you would like identified, feel free to submit photos for us to look at. Fortunately, chewed leaves should not cause serious harm to the plant's overall or long-term health.

Miri

Miri,

Hi Mike,

Thank you for the photo; no, it wasn't received the first time.

It's hard to say what caused this damage, though we can probably rule-out deer and rabbits since more leaf area would have consistently been eaten. This could have been caterpillars (several of our native butterfly and moth species use members of the aster family, which includes sunflowers, as host plants); a few feed in groups instead of being solitary. Caterpillars often leave the host plant when ready to pupate so they can be more hidden from predators, so they may be done feeding and have since wandered-off.

Slugs and snails leave an iridescent slime trail behind them, so unless you see this underneath the leaves, we can probably rule them out also.

For now, just periodically keep an eye out for any insects on the plant day or night. (Not all that may appear there will be those responsible for the chewing, though.) Since whatever ate the foliage appears to have gone (or is at least not visible now), no treatment is needed yet. If the plant's roots are healthy, we expect it will growth out of the damage. You can trim off the most heavily-eaten leaves for now if you prefer, but try to leave those only partially eaten as they are still feeding the plant via photosynthesis, and the faster it can recoup its energy reserves in this way, the faster it will be able to replace foliage.

Miri

Hello Miri,

Hi Mike,

These appear to be Blue Mistflower (Conoclinium coelestinum) and a type of Evening Primrose (Oenothera). The former is native; the latter is mostly native, but some are not (about a dozen species occur in MD, though some are much more common than others). Both can potentially self-seed with abandon, but are easy to weed-out if growing where you don't want them. Both are also valued by pollinators and should be fine to keep.

For future reference, you can submit a new question for queries unrelated to the original submission.

Miri

Thanks again! Appreciate your help.  You are awesome