Manipulating Chieftain tuber size profile with gibberellic acid seed treatment and vine kill date adjustment

According to the USDA AMS, the average price for smaller C size red potatoes was twice that of the larger A size. With size being a significant determiner of crop value, reliable methods for controlling size profile would be highly beneficial. While previous research has shown both treatment of seed with GA and vine kill timing to be effective in managing size profile, the response to treatments are often cultivar specific. Size profile response to combined treatments of GA and vine kill date has not been previously evaluated in the red-skinned cultivar Chieftain. In these trials, treatments included two GA seed spray treatments (0.009g a.i. MT^-1 and a water treated control) and four vine kill date treatments (85, 90, 95, and 100 days after planting), for a total of 8 treatments. GA seed treatment resulted in accelerated emergence (+34%), an increase in stem number plant^-1 (+33%), a trend towards an increase in tuber number plant^-1 (+11%), and a shift in size profile towards smaller C and B size classes (up to 29.9% of yield). Conversely, delaying vine kill was found to increase yields (+54%), while shifting tuber size profile towards the larger A+ size class (up to 56% of yield). Combined treatments of GA and vine kill date provide several strategies for increasing relative market value of the crop. For example, combining treatments of GA with delayed vine kill resulted in maximum yields while maintaining smaller tuber size, while GA treatment combined with early vine kill resulted in the maximum proportion of C size tubers.