Combine grated potatoes, beets, and onion in a colander; drain 15 minutes, pressing mixture occasionally to remove liquid. Place potato mixture in a bowl.
Lightly spoon flour into a dry measuring cup; level with a knife. Add beet greens, flour, salt, and pepper to potato mixture, stirring to combine. Slightly beat egg and egg white before adding into potato mixture.
Heat a large skillet over medium-high. Add 1 tablespoons oil; swirl to coat. Spoon potato mixture loosely into a 1/4-cup dry measuring cup, filling about two-thirds full. Add mixture to pan, and flatten slightly. Repeat procedure 4 times to form 5 latkes. Cook 3 to 4 minutes on each side or until golden brown.
Place latkes on a baking sheet; keep warm in oven at 250°F. Repeat procedure twice with remaining oil and beet/potato mixture, adding an extra latke to the pan during the last batch to yield 16 latkes total.
Combine sour cream with dill and horseradish; serve latkes with sour cream and applesauce.