Trim the leaves from the kohlrabi and slice off the root end. Peel the outer skin from the globes and cub each into 1/4 inch slices. Stack a few at a time and cut into julliene strips. In a large bowl toss the kohlrabi with 1 tablespoon salt and 1 table spoon sugar. Cover and refrigerate 3 hours. In a small bowl whisk together mayonaise, vinegar and apple. Toss. Transfer the kohrabi to a colander to drain excess mointer and return to bowl. Add mayonnaise mixture. Add more mayonnaise and black pepper to taste.