Potato prices plunged by 3 per cent to Rs 845.20 per quintal in futures trade today after traders offloaded positions,triggered by new arrivals from producing belts. At the Multi Commodity exchange,potato for delivery in October plunged by Rs 26.20,or 3.01 per cent,to Rs 845.20 per quintal,with a business turnover of eight lots. Marketmen said adequate stocks availability in the spot market due to fresh arrivals from producing belts and subdued demand mainly pulled down potato futures.