A canopy development model for potatoes

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(C) software program.