My Hibiscus plants have dozens of buds but just prior to flowering something chews thru the stems, about an inch blow the buds. They fall to the ground.

What can I do I wonder?

Do you see white bugs or eggs on or under the leaves? Might be mealy-bugs. One way to deal with them is to make a weak soapy solution with plain dish washing soap and water and spray the leaves and stems from above and below. Sometime just a forceful spray from the garden hose alone or as a follow-up to the soap spray. Most likely will have to be repeated frequently as they reappear.

If they are established plants, you cut prune them way back and make sure you bag the cut pieces or the problem will come back again. If the plants are well established and otherwise healthy, they should come back fairly quickly.

It also could be the hibiscus beetle. A little black beetle that bores a round hole in the base of the flowers .( if it is the beetle you should be able to see a few inside the flower). Use pyrethrum if u must spray other wise leave them as the common Hibiscus such as rosa sinensis or Hawaiian hibiscus flowers heavily and the flowers only stay briefly on the plant. Make sure the soil is slightly acidic - similar to gardenias and don't use too much nitrogen especially when flowering. I always find best result with hibiscus is to prune heavily to thicken the plant up and you will have so many flowers that it doesn't matter if a few get eaten.

Having a second look at them it looks like a scale - same remedy or the warm soapy water Suradit recommends. .

Thank you very much for the recomendstions.

Will trim back & spray.

I started the plants from cuttings and was excited to see dozens of buds on each plant.

Frustrated to see them dropping off.

Adding some coffee to the soapy water should help too, if you don't want to use pyrethrum.