b'Preventing Bruise in PotatoesFrom general tips to variety-specific recommendations, these experts deliver thegoods on mitigating bruise.BY: MELANIE EPPMEETING THE DEMANDS of processors and buyers in terms of quality is aHigh levels of calcium in the tuber reduce the risk of bruising at harvest constant challenge for producers. Potatoes that dont meet quality specs areand during transportation, as calcium is important for cell wall structure, says either reduced in price or get rejected entirely. All through the production process,McMillan. Calcium uptake varies from variety to variety; using calcium nitrate there are steps growers can take to assure the highest level of quality is main- rather than ammonium nitrate minimizes bruising damage, and in some varieties, tained, particularly when it comes to mitigating bruise.damage can be halved. There are three types of bruising that occur in potato tubers. Shatter bruise andLow boron levels inhibit calcium uptake, making boron equally important. blackspot bruise are associated with harvest, although bruise can occur anytimeBoron is also important for stabilizing calcium in the cell walls. they are handled. A third type of bruise, pressure bruise, occurs in storage.Low potassium levels can lead to issues with quality, hollow heart and Shatter bruise is visible to the naked eye. Tissue separation and peridermbruising. If potassium is under 10 per cent in the first tissue sample, it needs to be damage occurs when potatoes are harvested and handled when pulp temperaturesaddressed immediately, says McMillan. are too cold. Visually, shatter bruise appears as cracks and fissures in the skin.While mitigating bruise is a season-long process, the most vulnerable time for Crisp, turgid potatoes or potatoes with high-solid content rebound when hitthe potato is harvest, explains Peter VanderZaag, co-owner of Sunrise Potato in with a physical blow. As force reverberates through the potato tuber tissue isOntario. Management begins with proper adjustment and operation of harvesting actually torn apart. The result is cracks and fissures.equipment and placement of padding in problem areas of the handling equipment. Blackspot bruise is not visible to the naked eye, but occurs beneath the skinsAvoid drops of more than six inches. The recommended pulp temperature range for surface. In this case, the outer skin and the tissue beneath it deform in responseharvesting tubers for storage is between 7 and 20 C.to a blow, but the skin doesnt break and tissue remains intact. Instead, the blowHowever, the temperature range for harvest can be narrower for some varieties, damages internal cells where enzymes and substrates react to create discolor- warns VanderZaag. The new Frito-Lay varieties, for example, are very sensitive ation. Blackspot bruise tends to occur at warmer pulp temperatures or during dryto bruising, in part because they have higher dry matter, he says. For higher dry conditions.matter potatoes, the safe harvest window is 18 to 12 C.Similar to blackspot, pressure bruise damages tissue inside the tuber, leadingSoil moisture at harvest also contributes to bruise. In Western Canada, growers to discoloration within. In this case, bruise is the result of the weight of the potatocan easily irrigate when rainfall is scarce, but in the eastern parts of the country, pile, which bears down on the potatoes at the bottom of the pile. Externally,soil is oftentimes too wet or too dry come harvest. Harvesting in soil that is both potatoes appear flattened.too wet and too dry can lead to bruising. What weve done to overcome this, really, is to double up on equipment, so when GOOD NUTRITION CRUCIAL TO BRUISE MITIGATION the days are right, we can harvest twice as fast as before and then we work fewer Mitigating bruise starts with plant nutrition, says Emmerson McMillan, YaraVitadays, says VanderZaag. When conditions are not right, then you take the day off. specialist with Yara Canada. Low potassium, boron and calcium levels all contrib- Time of vine kill can also play an important role in bruising. Some varieties ute to bruising.require as much as three weeks of vine kill before you can harvest. 18 SPUDSMART.COM FALL 2019'