I don't know what they are but it sounds like what my mother and I have had in our gardens this year. Are they tiny worms that are an off-white color? I discovered something similar in my garden this year but it didn't attack my marigolds -- they liked my dusty miller, though, and killed all 3 plants. My mother had those little worms in her garden and they killed her glory bower.

It starts with the plants drooping, as with a lack of water...watering them temporarily perks them up, but they quickly wilt again and get to the point where no amount of watering perks them up. Soooo, you finally start digging around, looking for the source of the problem, pull on the stems a bit and the entire plant easily pops right outta the ground, which is where we've found the worms...in the ground directly around the plants, and in the stems.

Sorry to ramble on like this, since I don't have a clue what those worms are. Have you tried the pests & diseases forum?

Renee

I've had problems with slugs eating mine. In WV slugs and japanese beetles are the only problem I have with outdoor gardening.

I am having the same issue right now with my marigolds as well as osteospermum in the same flower box. These worms are light beige striped and they are fairly small. They have bore a hole in every bud on the marigolds. On the osteospermum they have spun a web around all the petals encasing themselves inside the blooming flower. I have never had this pest before and would love to know what it is and how to deal with it!