Why are exports of Bengal's famous Himsagar mangoes to US at risk?

US shipments of West Bengal's famous Himsagar mangoes face risk after dark spots appeared on a significant portion of the crop, PTI reported. "Continuous rain during the bagging period, followed by high temperatures, led to the problem," an exporter said. Despite disease affecting about 15% of bagged fruits, a mango union president said, "Nearly three lakh more...mangoes are still available."