Comparison of Diquat, Glufosinate, and Saflufenacil for Desiccation of ‘Dark Red Norland’ Potato

Chemical desiccants are commonly used to regulate tuber size, strengthen skin, and facilitate harvest for potato (Solanum tuberosum) production. Glufosinate is labeled for potato vine desiccation; however, limited data are available. Saflufenacil, a protoporphyrinogen oxidase–inhibiting herbicide, is an effective desiccant in other crops. Field research was conducted to evaluate glufosinate and saflufenacil as desiccants applied to ‘Dark Red Norland’ potato. Desiccants consisted of diquat, glufosinate, saflufenacil, glufosinate plus carfentrazone, and glufosinate plus saflufenacil applied at three timings, DESIC-1, DESIC-2, and DESIC-3, when size B potatoes averaged 43%, 31%, and 17% of total potato weight. Potato vine desiccation was more difficult at DESIC-1 and DESIC-2 because of immature vines. Diquat was the most effective desiccant 7 days after treatment (DAT), desiccating potato vines 88% at DESIC-1 7 DAT. Glufosinate alone desiccated potato vines 65% at the same timing; however, carfentrazone and saflufenacil added to glufosinate increased vine desiccation 8% and 16% compared with glufosinate alone, respectively. Vine desiccation by all treatments ranged 99% to 100% at 14 DAT. Desiccant and timing effects on skin set were determined using a torque meter before harvest. Skin set resulting from all desiccants and timings ranged between 1.88 and 2 lb-inch, and no significant differences were observed. No significant differences in yield were noted among desiccants. This research indicates that glufosinate and saflufenacil are suitable alternatives to diquat for potato vine desiccation; however, safety of saflufenacil applied to potatoes before harvest has not been determined.

Weed Control in Tomato

Revised! HS-200, a 5-page fact sheet by William M. Stall, explains the increased importance of weed management in tomato production due to the introduction of the sweet potato whitefly. It discusses management in all areas of the farm, as well as post-harvest vine desiccation. Includes a table listing chemical weed controls for tomatoes in Florida. Published by the UF Department of Horticultural Sciences, November 2007. HS200/WG040: Weed Management in Tomato (ufl.edu)

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 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. Key words: Diquat, flailing, Russet Burbank, Shepody, Ranger Russet, Russet Norkotah

UCC-C4243 Dessication of Potato Vines

Chemical vine desiccation of potato (Solanum tuberosum L.) is widely used in the USA. Diquat is the major vine desiccant but has some drawbacks such as incomplete stem desiccation allowing regrowth. A new herbicide, UCC-C4243, was evaluated as a replacement for diquat. The potato cultivar `Atlantic' was treated with UCC-C4243 (a.i.) at 0.25 to 2.5 oz/acre (17.5 to 175 g·ha-1), and leaf and stem desiccation efficiency was compared to diquat (a.i.) at 4 oz/acre (280 g·ha-1). Split applications of UCC-C4243 were compared to double applications of diquat. Subjective evaluations were made on regrowth and tuber skinning, and objective measurements on specific gravity and yield. Trials were conducted from 1991 to 1995 at Scottsbluff, NE. UCC-C4243 at 1.5 oz/acre (105 g·ha-1) and higher significantly increased leaf and stem desiccation compared to diquat. There was no difference between single and split applications of UCC-C4243. UCC-C4243 suppressed regrowth at 1 oz/acre (70 g·ha-1) and prevented it at 2.5 oz/acre at 3 weeks after treatment while diquat did not. Skin set of tubers was promoted equally by all desiccants. Specific gravity was not lowered by UCC-C4243 but was by diquat. Yields were not affected by either UCC-C4243 at 1.5 oz/acre or diquat at 4 oz/acre. UCC-C4243 was more effective than diquat as a vine desiccant without the regrowth and tuber specific gravity effects associated with diquat.