When fall arrives and leaves start changing color, Mike Valladao, a systems engineer at a cybersecurity company, slips into his alter ego, “Farmer Mike," also known as the “Picasso of Pumpkin Carvers.”

Farmer Mike has been chiseling whimsical faces and comical creatures into big pumpkins for more than four decades. Wearing his trademark orange overalls and farmer hat, he's sculpted hundreds of gourds into ghoulish faces, seaside landscapes, witches, dragons and pop culture figures such as Yoda and Charlie Brown .

Valladao doesn’t have any formal artistic training, but he's always looking for inspiration. He gets ideas from looking at art in a museum or just walking down the street.

“Sometimes I’ll look at somebody and I’ll think, oh, I like the teeth or I like ears or the way the nostrils flare," Valladao said.

This year, “Farmer Mike” celebrated 40 years of Halloween artistry at the Half Moon Bay Art & Pumpkin Festival, which is held in mid-October and is best known for its giant pumpkin weigh-off.…