Sudden damage on young ornamental sunflowers
While I was away on travel for four days, something attacked my very healthy and happy 2-month-old sunflowers (started from seed). They were all chewed up and had small, 2/16" - 3/16" long, very oddly shaped insects on them that look to be treehoppers. There are also pale, scarred sections on the main vein of mature leaves. The insects mostly let me squash them, but occasionally one will shoot off as I get close. The plants that are most chewed up are the ones with the highest concentration of these insects. The information on treehoppers says that they suck sap; but could they be causing all the chewing damage that suddenly appeared? The only other insects that I found on the plants were ants, and they seemed to go away after I squashed as many of the insects in the uploaded pictures that I could find. There were anywhere from a few to two dozen on any specific sunflower. I did not see any damage, or these particular insects, on any other plants in the area, including lettuces, marigolds, zinnias, nasturtiums, tomatoes, herbs, and so forth.
Baltimore County Maryland
Neither the tree hoppers nor the ants could inflict the damage you're seeing because they don't have the correct mouth parts. Ants are beneficial. Try to conserve them. The tree hoppers are incidental.
The chewing damage on your sunflowers indicates a larger chewing pest, probably slugs, possibly some kind of beetle. Slugs are nocturnal, which would explain why you haven't seen them. See our website fact sheet for help with slugs: http://extension.umd.edu/learn/slugs-and-snails-hg92
If beetles are the cause, they are either already gone (since you can't find them) or they are nocturnal. You can go out at night and look for critters on the leaves with a flashlight if you think this may be the culprit.
Thank you so much. We put out slug traps, a saucer with a home yeasty brew, and the next morning it was loaded with small earwigs ! The next night, same results.
Earwigs have been known to feed on Echinacea, so it seems logical that they might nibble on sunflowers, as well. Another good trap for earwigs is a dampened, rolled up newspaper laid near the plants. They will crawl into the paper for cover each morning.