Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
auctumno (correctly aut-), āre, v. n. [auctumnus], to cause or bring on autumn (only in the two foll. exs.): corus autumnat, Plin. 2, 47, 47, § 124: aër aestate nimbosā semper quodam modo vernat vel autumnat, id. 2, 50, 51, § 136.