Abstract
Potato (Solanum tuberosum L.) planting in Northeast Florida's Tri-County Agricultural Area (St. John, Putnam, and Flagler counties, TCAA) typically runs early January through mid-March. Six planting dates (PD) (13 January 2004 and every two weeks, thereafter, to 25 March 2004) and two chipping varieties ('Atlantic' and 'Harley Blackwell') were evaluated to determine key growth and development stages (emergence, full flower, and senescence), yield and quality based on accumulated growing degree days (GDD-7C base). 'Atlantic' is preferred for its chipping quality and high yield, but is susceptible to internal heat necrosis (IHN). 'Harley Blackwell' is noted for its resistance to IHN and comparable chipping quality to 'Atlantic'. Growers in the TCAA have historically used calendar days to predict key potato developmental stages. Developing a growing degree day system may be a more accurate predictor of these stages throughout the season to determine optimal planting dates and yields compared to calendar days for chipping varieties in the TCAA. For both varieties and all planting dates, 'emergence' and 'full flower' occurred approximately at 213 and 804 accumulated GDD, respectively. Accumulated GDD at harvest for PD's 1-6 were 1493, 1676, 1951, 2374, 2490 and 2840, respectively. As accumulated GDD at harvest exceeded 2374, total and marketable yields decreased on average 17 and 20%, respectively.
