Mystery blotches on peach skin - what we know and don't know about bronzing

Blotches on peach fruit skin, commonly referred to as 'bronzing' have been observed in several peach growing regions (North America, Central America, and Mediterranean Basin). In recent years, it has become a major issue for peach producers in the southeastern United States, and it has been reported by growers in other states in the US. Symptoms occur as irregular-shaped blotches ranging from a single blotch to covering almost the entire fruit. The blotches are yellow at first but then turn to a bronze color after a few days of storage. It is a problem that occurs during ripening especially in years with high rainfall preceding harvest. In contrast to a skin disorder with similar symptoms described for California peaches called 'skin burning', bronzing is initiated in the field prior to harvest and symptom severity intensifies during storage. We do not know yet its underlying cause nor are there management recommendations in place. However, we found no evidence of fungal pathogen, insect, phytoplasma or pesticide involvement. Rapid cooling and storage exacerbate but do not causes bronzing. New evidence based on symptom patterns suggest that water relations in the fruit perhaps associated with the lack of supply of nutrients and/or yet undescribed viroids may be a predisposing factor to bronzing.