We have 2 gardenias that have been struggling this year. The problems include leaves that turn yellow and drop, younger (thin branches) dying, and many areas where something has removed the outermost layer of bark on the larger branches revealing the green tissue underneath. The size of the removed areas can be 1/4 inch wide by 1-2 inches in length, although some are much wider. I suspect that the issue with the bark is the primary factor and want to make sure that I treat it and not damage the plants. I have not seen any visible pests like whiteflies, scale or mealy bugs. We have been using a systemic (Bayer) pesticide/fungicide/fertilizer around the base of the shrubs every 6 weeks for the past few years as part of our regular plant care routine.

First, I would be interested in what may be chewing on the branches and then what measures I can take to stop it from happening.

If the pests are insects, would a general (broad range) insecticide be effective? Are there any pesticides that I should not use with gardenias?

Although I have not had any problems elsewhere in my garden with them, could there be a non-insect pest (slugs, snails) that are responsible?

Thank you!