Freeze Risk and Protection Measures of Satsuma Mandarins Grown in the Southeastern United States

Abstract

The northern fringe of the Gulf of Mexico has an excellent climate for growing high-quality satsumas that are available in U.S. retail chain stores before most other citrus. In part because of high fruit quality, satsuma mandarin production grew into a major industry in Alabama, Louisiana, Mississippi, and the panhandle of Florida in the early 1900s. Freeze protection measures were not sufficient to prevent devastation of the industry by severe freezes. For the period encompassing the late 1900s, freeze risk was estimated using a mathematical approach that determined killing temperature based on air temperature. Freeze injury was determined to occur 1 out of every 4 years on average, although the freezes tended to come in clusters that have as yet not been correlated with long-term climate patterns. Within-tree microsprinkler irrigation, which was not available in the early 1900s, has been shown to reduce the severity of injury. Within-tree microsprinkler irrigation allows full production the year after the freeze, whereas unprotected trees must be grown from the base or replanted. The northerly geographical limit in the southeastern United States whereby satsumas can be successfully grown commercially is currently not known. Methods of protecting the entire tree, including overtree microsprinkler irrigation plus windbreaks and high tunnel houses, are being evaluated. More cold-tolerant satsuma cultivars have been selected, but they reduce freeze risk by at most 2 °C in this region compared with current commercial cultivars. Genetic modification is one possible mechanism for improving cold tolerance sufficiently to reduce freeze risk similar to that of the citrus industry in Florida.