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22 POTATO GROWER | AUGUST 2017 Diggin' In Diggin' In Diggin' In Diggin' In Diggin' In Diggin' In HARVEST | By Nora Olsen and Mike Thornton, University of Idaho Data is powerful in minimizing bruise On-farm Bruise Assessment A great tool to identify where bruise may be occurring in your harvest and handling operation is to take tuber samples at various spots, warm them, and evaluate for the level of damage. Creating your own quality assessment protocol allows you to take into account the physiological (nutrient, maturity, specific gravity) and physical (hydration level, temperature, shape, size) aspects of the tuber that contribute to both shatter and blackspot bruise susceptibility—as well as identify the locations of greatest impact. The assessment encompasses all the complex components contributing to bruise formation for your operation and variety. Unfortunately, it is a laborious chore. The game is to hasten the process so changes to equipment or harvest timing can be made as soon as possible. The development of blackspot bruise takes time after the force of impact damages the cells. The blue-black discoloration is the formation of a pigment called melanin. It typically takes about 24 to 48 hours for the pigment to develop at room temperature. However, the higher the temperature, the quicker the pigment formation will occur, and the sooner the results will be available. Shatter bruise can be rated without warming tubers, but it is often difficult to see each fissure or opening. We have outlined a few strategies to use in developing an on-farm bruise assessment. SAMPLING Select various points along the harvest and handling operation to take samples (20 to 25 tubers at each spot). Identify areas or equipment that may have a greater impact on the potatoes. Common points are after the windrower, after the harvester, off of trucks, various drops in conveying, and in the pile. Properly denote each sample bag of potatoes with field and/or variety, which piece of equipment or point of sampling, date and time, and pulp temperature. If you are running more than one windrower or harvester in the same field, know which sample is taken from which piece of equipment. Timing may be off on one windrower but not the other. The idea here is to identify where the cause of the bruise is coming from. If you are primarily focused on identifying impacts resulting in shatter bruise, after collection, wash tubers and evaluate for damage. See below for an example on how you can evaluate and rate the samples for shatter bruise. If you need to assess for blackspot bruise, the samples must be warmed to hasten the process. Blackspot color will develop after about 48 hours at 50 degrees Fahrenheit, about 24 hours at 70 degrees, and 6 to 12 hours at 90 degrees. Time needed for color to form will be variety- and field-dependent. There is no need to wash the potatoes first, but keep them in the dark. Commercial "hot boxes" are available for purchase to warm samples. These boxes are handy, since they are designed to handle higher temperatures, although they are often smaller and can only hold a few samples at a time. Other options are to set samples in a mechanical area where heat is given off by equipment or find or construct a room where a space heater Growers should inspect tubers at various points of the harvest and handling operation to assess damage from blackspot and shatter bruise (inset).