When you wash your hair too often, you are stripping the natural oils from you scalp and encouraging the production of more oil. Most people wash their hair too often, so the transition to a once-weekly routine is a bit of an adjustment - your scalp needs to get used to the new production schedule!  Also, your loose hair was constantly swooshing over your scalp distributing those oils - your dreads, not so much. All this to say, that plaque-y buildup is caused by an excess of oil with nowhere to go.

To help get rid of any buildup, and to help your scalp start to right itself quicker, mix up a vinegar rinse for just pennies! Take one part white or cider vinegar (your call) and 9 parts water. Either use a spray bottle or just pour it over your scalp. Let it sit for 20 minutes, then rinse it out with just water (no shampoo!) until the smell dissipates.