These look like Spittlebug "nests," a common insect related to leafhoppers that fortunately doesn't tend to cause any noticeable damage to plants. They can be fairly easily blasted off the plant with a strong spray of plain water from a garden hose, which will either knock the insects off with their bubbles, or expose them long enough for some predators to potentially eat them. No insecticide use is needed, nor would it reach them well enough to work through the bubbly covering over their bodies.

Miri