This particular plant I believe is one of two Helianthus - Helianthus divaricatus (Woodland Sunflower - smooth stemmed) or Helianthus laetiflorus, possibly var. rigidus (Showy Sunflower - rough stemmed.)

While difficult to determine the stalk in the picture, the stalk appears "fuzzy", if so, and rough to the touch, then I would lean toward the second of the two listed above.

Both grow to 6 - 6 1/2 feet and bloom into October. 

Being able to better view the complete leaf (e.g rough, hairy, rigid, veining) and  length of the petiole (leaf stalk) would help make the decision between the two Helianthus!