MILFORD — Polaris Industries plans to close its plant in the northwest Iowa city of Milford, leaving up to 300 employees out of work. Polaris spokeswoman Kelly Basgen said on Monday the company would stop production of all-terrain and utility vehicles at the Milford plant that had operated since 2013. Production would shift to plants in Alabama, Minnesota and California. Basgen says some employee could move to other Polaris plants, leaving between 275 and 300 workers out of a job.