The Influence of Ethephon Application Timing and Rate on Plant Growth, Yield, Tuber Size Distribution and Skin Color of Red LaSoda Potatoes

Optimizing the response of growth regulators depends in part on finding the most appropriate application rate and timing. Preliminary trials indicate that ethephon (2-chloroethylphosphonic acid) may be useful for improving potato (Solanum tuberosum L.) tuber appearance and skin color of red-skinned cultivars, but relatively little is known about optimum application practices. Two separate trials were conducted at the University of Idaho Parma Research and Extension Center to evaluate the effect of ethephon foliar application timing and rate on plant growth, tuber yield, size distribution, and skin color of the cultivar Red LaSoda. Skin color was rated visually and by colorimeter at harvest and periodically throughout storage at 4 °C. In 2011, ethephon application timing did not influence plant height, total yield, tuber size or skin color but did affect some tuber size classes. In contrast, all of these parameters were significantly influenced by application timing in 2012. The optimum application timing to influence skin color was a relatively narrow window during initial flower development, to 10 days after initial flowering (coinciding with tuber initiation). Increasing rates of ethephon significantly reduced plant height, increased foliar injury symptoms, and reduced average tuber size, but did not influence total yield in Red LaSoda. Higher ethephon rates resulted in significantly darker tuber skin (lower L* values) and increased red color (increased chroma and reduce hue angle values) when compared to the non-treated control. Evaluation of samples held in storage showed that differences in skin color ratings at harvest were maintained throughout the storage period. It is concluded that two foliar applications of ethephon at a rate between 292 and 438 ml ha−1applied ten days apart, initiated at pre-bloom, will provide the optimum change in skin color and reduce average tuber size without reducing total yield.