Hi, 

They look like the egg sacs of Cottony Camelia Scale. The link provided will give you some detailed information for them. What you're doing by picking off and squishing is a good process to do while the population is manageable so that you don't have to use a chemical to control. 

It is still too early for any horticultural oil at this point. We need to be at 649 degree days and last week Gaithersburg was measuring around 333. Usually around mid-June is when the crawlers start to emerge and you can treat for them. If you notice red ladybird beetles (Lady Bugs) they are natural predators and doing the job for you - so we wouldn't recommend any spray at that point. 

You can review the general management for scale webpage for more details on different management strategies. If you choose to use a hort. oil for the growing season crawlers, you can keep monitoring for the degree days when you can spray. Spray at 1% and make sure you thoroughly coat the leaves on all surfaces. You can use a dormant oil application in the winter. 

Let us know if you have further questions with management or applications. 

Emily