Contaminants and injury induce inking on peaches and nectarines

After 3 years of study, we have demonstrated that physical injury combined with contamination cause skin discoloration, called inking, on peaches and nectarines. Abrasion damage releases anthocyanin/phenolic pigments, which are located in the skin cells, allowing the reaction of these pigments with the heavy-metal contaminants. We found that iron, copper and aluminum were the most deleterious contaminants of those studied in inducing inking on abraded fruit. Approximately 10 ppm iron was enough to induce inking at the physiological fruit pH (~3.5). This contamination can occur within 15 days before harvest, or during harvest or packing operations. Foliar-nutrient, fungicide and insecticide preharvest sprays may act as sources of contamination for inking development, depending on the preharvest application interval. To reduce inking incidence, we have developed safe preharvest application intervals that yield low inking incidence benomyl for iprodione (Rovral), triforine (Funginex), vinclozolin (Ronilan DF) (Benlate) and certain foliar nutrients containing heavy metals.