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14 POTATO GROWER | AUGUST 2018 By Yi Wang & Amanda Gevens, University of Wisconsin-Madison What is pink eye? Pink eye is a disorder of potato tu- bers that can cause costly storage losses for potato growers and can reduce tuber quality to the point where tubers will be rejected by potato processors. Pink eye not only di- rectly affects tubers, but also makes tu- bers more susceptible to diseases such as Pythium leak, bacterial soft rot, pink rot and Fusarium dry rot. These diseases cause additional storage losses and reduc- tion in quality. What does pink eye look like? Pink eye is characterized by a short-lived external pink color that is often, but not always, found around the potato eyes of freshly harvested tubers. Eyes at the bud ends of tubers (i.e., those farthest from where tubers are attached to stems) more commonly show pink eye symptoms. Pink eye can eventually devel- op into corky patch/bull hide, which in- volves a thickening of areas of tuber skin extending approximately one-tenth of an inch into the tuber flesh. Corky patch/bull hide can make tubers unmarketable for ei- ther fresh market or processing use. External pink eye symptoms are often ac- companied by brown patches in the tuber- flesh immediately underneath the skin. Browning due to pink eye can resemble browning due to other disorders such as internal brown spot or heat necrosis, but these latter disorders tend to occur deeper in the tuber (i.e., inside the vascular ring), rather than just underneath the skin. Pink eye can also be confused with late blight. If there is any question whether the problem might be late blight rather than pink eye, growers should contact their county extension agent for informa- tion on submitting a sample to a diagnos- tic lab for proper testing. Where does pink eye come from? Pink eye is a physiological disorder—an abnormality in plant growth— rather than a true disease that involves a disease-causing microorganism. Pink eye arises during periods of excessive soil moisture and warm temperatures, espe- cially during the later stages of tuber de- velopment. Pink eye symptoms typically appear within seven to 10 days after ex- cessive rain. Excessive soil moisture cou- pled with high soil temperature causes a lack of oxygen around potato tubers, lead- ing to damage of cells in the tuber skin. This cell damage contributes to pink eye development. Environmental conditions that lead to pink eye also promote tuber infections by the pathogens that cause Py- thium leak, bacterial soft rot, pink rot and Fusarium dry rot (all diseases associated with pink eye in storage). How do I salvage pota- to tubers affected by pink eye? Once pink eye symptoms develop, they are per- manent. If symptoms are minor, tubers may still be usable. However, when pink eye symptoms are severe, symptomatic tubers will be rejected and discarded. How do I avoid problems with pink eye in the fu- ture? Growers have no control over the extreme precipitation and high temperatures that promote pink eye development. However, growers can practice management strat- egies that minimize water-saturated soils and reduce warm soil temperatures, thus reducing the severity of pink eye. To minimize water-saturated soils, deep till areas where pink eye has been a prob- lem, areas where water tends to collect for extended periods, and areas where soils may be compacted (e.g., field entrances or headlands). Deep tillage will break up subsoils in these areas that impede prop- er drainage during wet weather. Proper drainage will limit periods when tubers will be oxygen-deprived and thus more prone to pink eye development. Grow- ers can also avoid any activities that will cause soil compaction such as operation of heavy tractors and field equipment when soils are wet. Minimizing water-saturated soils will not only reduce the likelihood of pink eye development but will also help limit development of other tuber diseases. To promote cooler soil temperatures, growers should be sure to manage diseas- es such as potato early dying that reduce canopy coverage. Loss of canopy allows soils to warm faster on sunny days, thus leading to higher temperatures that are more favorable for pink eye development. Finally, growers should scout for pink eye symptoms prior to and during har- vest. Knowing the severity of pink eye in a field can help growers make informed decisions about the appropriate duration for tuber storage and the best end use for symptomatic tubers. Understanding Pink Eye of Potato TOP