I just came back from a long ride out on smooth asphalt roads through the cornfields of central Illinois. It was around noon and pretty hot and during the way back, I began to notice my rear tire making all kinds of sounds. I looked down and it was completely encrusted with asphalt, small rocks, and other miscellaneous debris. The tires are high pressure slicks I recently switched to, which have a little tread. Oddly enough the front tires were relatively fine, although they do have the pebble here or there. See the attached photo below.
Is there a way to prevent this? Is there a way to remedy this afterwords? If this is unavoidable due to the road type/temperature, should I switch to 100% slicks (no tread)?