Vine desiccation characteristics and influence of time and method of top kill on yields and quality of four cultivars of potato (Solanum tuberosum L.)

Potato crops are typically flailed or chemically desiccated several weeks prior to harvest to promote tuber maturity and facilitate harvest operations. This study evaluated how yields and processing quality of several potato cultivars responded to mechanical top kill versus chemical desiccation with diquat at four different treatment dates. The influences of year and cultivar on the rate and extent of vine desiccation were also evaluated in the chemically desiccated crop. The cultivar Ranger Russet was slower to desiccate than Russet Burbank, Shepody or Russet Norkotah, likely because of its larger canopy. Averaged over 3 yr and four treatment dates, flailing reduced yields of the four cultivars tested by an average of 4% relative to chemical desiccation of the tops. The yield difference between flailed and chemically desiccated crops increased if conditions after application of the desiccant favored a gradual die down of the canopy. Specific gravities of the chemically desiccated treatments were equal to or higher than treatments killed by flailing. Fry colors were not influenced by either the method or timing of top kill. Although chemical desiccation enhanced yields relative to a crop flailed at the same time, the dry down period required for the chemically treated crop was at least 3 wk in this study. By contrast, crops killed by flailing are ready for harvest immediately, as long as skin set is not critical. Early in the season, if flailing allowed top kill of Russet Burbank to be delayed by as little as a week, the result was a 9% yield gain. As growing conditions became less favorable later in the season, there was little potential for yield gain by opting to flail instead of using the chemical desiccant.