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One of the most serious tuber quality concerns of US chip potato growers is stem-end chip defect, which is defined as a localized post-fry discoloration in and adjacent to the vasculature on the stem end portion of potato chips. The severity and incidence of stem-end chip defect vary with growing location and variety, but quantitative data describing this are not available. A multi-year and location study was conducted to evaluate chipping potato varieties for tolerance to stem-end chip defect formation and to quantify defect severity and incidence regionally and temporally. It was observed that higher night temperature in July and August compared to the regional 30-year history was consistently associated with higher SECD severity. Average SECD severity was linearly correlated with incidence of chips having severe SECD. Chip color and tuber stem-end glucose content were significantly correlated with average SECD score across all treatments. Multiple tuber samplings from early growing season to mid post-harvest storage demonstrated that some varieties, such as Nicolet and Pike, had fewer stem-end chip defects than other varieties across years and locations. Stem-end chip defect was rarely observed prior to harvest, but was apparent at the time of harvest on multiple varieties depending on the year and location. Tuber stem-end sucrose and glucose prior to harvest were not indicators of defect development at harvest and out of storage, but pre-harvest chip color was significantly correlated with defect severity 10 weeks after preconditioning was finished.

Potatoes (Solanum tuberosum) in Wisconsin are predominately grown on soils that have a high potential for agrichemical leaching. Weed control strategies are not designed for season long control from a single high rate herbicide application but for reduced rates combined with mechanical and cultural strategies. The current recommended herbicide rates provide 7–9 weeks of efficacy. Mechanical measures provide effective early season control, but development of crop canopy prevents cultivation after about four weeks. Past studies have shown that shade levels comparable to those in a potato canopy can significantly reduce weed biomass. This study was initiated to develop a canopy development model and evaluate the difference between Superior and Russet Burbank potatoes. Plots were established in 1988–1992 at the Hancock Agricultural Research Station on Plainfield loamy sand (mixed, typic Upsidaments). Light readings were taken both under the crop canopy and in full sunlight to determine the amount of shading provided by the crop. Physiological Degree Days (P-days) were used to monitor the development of the potato varieties. Regression analysis was used to determine if P-days could be used as a predictor for canopy development. Superior reached maximum canopy (88% shade) at seven weeks after emergence (WAE) and maintained it until 9 WAE. Russet Burbank reaches maximum canopy at 8 WAE (98% shade) and maintains shading above 80% until 13 WAE. The canopy model is an empirical relationship estimated using regression techniques, and is currently being utilized in a weed management module for the WISDOM © software program.