"Defining*Theft in Iowa. Under*Iowa*law, a person commits*theft*when he or she does any of the following: takes possession or control of another person's property with intent to deprive the person of that property."
You could probably also add trespassing and obstruction of the roadway.
I would try to argue intent to harm as well. Could driving over pumpkins harm the car and/or the person? Assuming this was a night too, so hard to see them Could cause serious injuries if it made the car swerve.