For the black streaks (I don't know about leaves etc) Buy a large bottle of Tilex at Wally World and a 1 gal hand sprayer (one time purchase on the sprayer). Pour in the Tilex (all of it) and fill with water. Roll out the awning and liberally spray the bottom and then roll up. Wait 15-30 min and unroll and rinse off. If you still have any stubborn streaks coat them and roll up for another 15-30 mins and then unroll and rinse again. Don't forget to rinse the top also.
My old trailer had a bad case of black streaks and it took 2 tries as described and it looked like new. No scrubbing, nothing. I had previously tried the RV Black Streak Remover and that was a waste of money.
Clif and Millie
Ozzie (half a dog tall & 2 dogs long)
2009 Ford Lariat F350 SRW CC Diesel
2013 Cruiser CF305SK Patriot Edition