#1 stiff-legged deadlift with dumbells.
stand with a dumbell in each hand, knees slightly bent, then bend over & touch the dumbells near your feet while keeping your back straight, then stand up (also while keeping your back straight).
this will strengthen your lower back.
#2 dumbell rows.
stand with a dumbell in each hand, then bend over at the waist (keep your back straight).
while bent over lower & raise the dumbells to your chest a few times, then standup.
this will strengthen your lats.