what is this bug? it ate all the leaves
Hi, I have attached 3 photos. I noticed on Tuesday night that from a distance the leaves looked like something was eating the flesh of the leaf. tonight, I discovered almost all of the leaves gone and these worm like things on the plant. I sprayed insecticidal soap on the plant. the worms reared up! I picked them off. sprayed the plant 3 times. the worms were everywhere on the plant. what are they? how can i prevent them? will the plant survivie? thank you.
These look like sulphur butterfly caterpillars. Cassia marilandica is a native plant and there are several caterpillars that use it as a host plant (they can only feed on certain plants during this life stage). Refer to the following webpage and see the information about "faunal associations" with Maryland Senna. https://www.illinoiswildflowers.info/savanna/plants/md_senna.html
If you want to manage them, you can wear gloves and remove the caterpillars by hand, dropping them into a container of soapy water. Another option would be to apply a biological product called Bacillus thuringiensis (Bt) which controls caterpillars. Perennial plants can tolerate some insect feeding damage and survive to return the next year. There is nothing you can do to prevent the caterpillars from coming to the plant. Monitor the plant earlier in the season next year and you can remove caterpillars by hand when you first see them. This will help to reduce the amount of damage.