"they seldom do really great harm...." Unless of course, their damage removes so much chlorophyll that the leaves CAN'T do what they are supposed to do. A large population of these insects can also result in the loss of other plant juices in large quantities. I've seen this occur on azaleas, pyracantha, and lantana, just to mention three of the common hosts of lacebugs. Such damage is common and not in the best interest of the plant to ignore. OF COURSE, measures should be taken to restore the plant to a healthier status by controlling the pest. There can be up to 5 generations per year in a warm climate!! But I agree with Jean, the images don't really indicate lacebug damage, though that stippling could make one think so. Here's a question: what does the UNDERside of those affected leaves look like? The bottom of lacebug infested leaves will always be covered with dark fecal matter and the tar-like spots which cover their egg clusters. Very dirty. Is that what you see? Here is a link that might be useful:

I disagree with the sentiment being expressed by some here that sycamore/plane is too large-growing a species for this site. This is a street tree, and if you follow the design criteria intended for street trees-primarily to shade the streetside, produce a green canopy, reduce the overwhelming presence of today's ultra-wide streets, intercept rainfall, provide an implied sense of security (from traffic) to pedestrians.....that's the start of the list....this is an ideally-sized species. We're seeing way too much of the downsizing of street trees in this country, whole series of lollipops on sticks which will never contribute in a meaningful way to our urbanscapes. As to cultural issues of this individual tree, I think others have covered those issues, although some here seem not to know that sycamore/plane has a peeling, exfoliating bark that ultimately becomes one of the trees best aesthetic characteristics. Those aren't trunk wounds, that's just the trunk! +oM

Definitely an azalea lace bug infestation!! Control can be done any time but best to time for when plants are not exposed to full sun - i.e., early morning or late evening or on an overcast day. Azalea lace bug control. I tend to lean to Neem oil for this sort of problem - very effective and a natural control.

The effectiveness of any spray for lace bugs depends a great deal on timing except in the case of systemic insecticides. Oil based sprays are very safe and can be effective against lace bugs when the pests are in the nymphal stage. They are much less effective against the adults Your county extension service can provide you with best timing in your area. Adult lace bugs are less than 1/8" in size and are very hard to see. What we usually see on the underside of rhododendron leaves is the shiny residue of lace bug excrement. What I'm suggesting is that you make sure the damage you've seen is from lace bugs. Thrips and mites produce a similar appearance and would be more difficult to control. Also, unless you're dealing with an absolutely enormous plant, a gallon of spray for one rhododendron is really excessive. The best control for lace bugs is to apply a systemic drench at the proper time. There are many issues with this approach, so become informed about them before deciding to use one.