import io
import pandas as pd

s = """something a b c d message month day year
one 1 2 3.0 4 NaN 10 10 2018
two 5 6 NaN 8 world 10 16 2018
three 9 10 11.0 12 foo 11 15 2018"""

print(pd.read_table(io.StringIO(s), sep=' ', parse_dates={'date': ['month', 'day', 'year']}))