Reduced Metribuzin Preharvest Interval on Potato Yield and Tuber Quality

Metribuzin has a 60-d preharvest interval (PHI) in potato, which limits utility of metribuzin POST in potato. In certain years, the potato may not fully cover the area between the potato rows. This allows for late-season weed emergence and subsequent yield reduction through direct competition or harvest interference. Field experiments were conducted in 2011 at Castle Hayne, NC; Freeville, NY; Hasting, FL; and Plymouth, NC to determine the effect of a 30-d PHI on potato crop tolerance. The cultivars planted were 'Superior' and 'Yukon Gold' in Castle Hayne and Plymouth, 'Castille' and Yukon Gold in Freeville, and 'Atlantic' in Hastings. Treatments included metribuzin at 278 g ai ha(-1) PRE, 30, and 60 d before harvest (DBH), and metribuzin at 556 g ha(-1) at 30 and 60 DBH. Split application treatments included metribuzin at 556 g ha(-1) at PRE followed by metribuzin at 556 g ha(-1) 30 or 60 DBH and metribuzin at 842 g ha(-1) PRE followed by metribuzin at 278 g ha(-1) at 30 or 60 DBH. Potato injury was <= 8% at all locations, and injury was transient. There were no differences observed between metribuzin rate or application date for individual potato grades or total yield. Reducing the PHI in potato to 30 d would have no effect on yield and would provide a longer period for controlling broadleaf weeds.