Cold-hardy citrus for North Florida By Xavier Martini and Peter Andersen old-hardy citrus has a long history in North Florida, Alabama, Louisiana and Georgia. Records show that sweet orange, citron, lemon, lime and pummelo were brought Figure 2. A young citrus reset covered in to Saint Augustine, Florida, from Spain in 1565. However, ice from microsprinkler irrigation helps C reduce cold injury to the tree. it was not until the late 1700s that the Jesuits introduced satsuma (Citrus unshiu) to what is now Louisiana. about 12 to 14 F. They mature and are harvested during a four-week SATSUMA HISTORY AND States, including major cities such as period centered in mid-November. RESURGENCE New York and Chicago. The combined To avoid peel tearing, satsumas must The satsuma is believed to have effects of freezes, hurricanes and the be clipped to be harvested and should originated in China, but it was first lack of workforce due to World War II be handled with care because they reported in Japan in about 1300. eliminated the satsuma industries on are more prone to bruising than most During the late 1800s, the Owari cul- the Gulf Coast until the 1990s. other types of citrus. tivar was introduced from Satsuma, The relatively mild winter tem- Japan, and was established through- peratures during the last three decades VARIETIES FOR NORTH out the lower Gulf Coast states. The and the development of microsprin- FLORIDA acreage of satsumas was virtually kler irrigation in the early 1990s to Currently, there is an urgent eliminated in the states bordering the reduce the effects of freeze (Figure 2) need to diversify fresh-market northern Gulf of Mexico by severe have led to a resurgence of interest in citrus in North Florida to include freezes in 1894 and 1899. cold-hardy citrus in North Florida. varieties that mature from September However, the satsuma acreage Satsumas are the most cold-hardy through December. rebounded. By the 1920s, Florida’s commercial citrus and account for a At the University of Florida Jackson County had billed itself as the great majority of the new commercial Institute of Food and Agricultural “Satsuma Capital of the World.” There citrus acreage in North Florida. In Sciences (UF/IFAS) North Florida were about 23,000 acres of satsumas 2017, the acreage of citrus by county in Research and Education Center in at that time (Figure 1), and the fruit North Florida was as follows: Gadsden, Quincy, many varieties and numbered was marketed as “Sugar Sweet.” The 120; Jackson, 31; Jefferson, 30; Taylor, selections have been under evalua- highest yield occurred in 1923, when 34; Madison, 30; and Suwannee, 20. tion for up to 13 years. The coldest satsumas were sold in the Northern When properly cold acclimated, temperatures recorded in Quincy for and Midwestern regions of the United satsumas are cold hardy down to the winters of 2015–2016, 2016–2017 and 2017–2108 were 26, 26 and 20 F, respectively. The last 10 years have experienced temperatures as low as 15 F, and Navel, Minneola Honeybell and Valencia have not experienced damage other than tip burn. Satsuma did not sustain any significant cold injury. In North Florida, microsprinkler irrigation for cold protection is imper- ative, especially for the non-satsuma varieties. Nevertheless, low-lying areas that can serve as frost pockets should be avoided, if possible. To reduce wind speed during freeze events, it is highly Figure 1. Satsuma grove in Milton, Florida (1929) advisable to select a location that is 16 Citrus Industry June 2018 protected by woodlands or other barri- ers on the north quadrant of the grove. The citrus varieties that mature CRDF 2018 Funding before Christmas have the best chance for success in North Florida since Cycle Is in Full Swing citrus fruit will freeze in response to prolonged temperatures of 25 to 27 F. n April 24, the Citrus Research and Development Foundation (CRDF) Researchers are particularly interested board of directors approved research priorities for two separate research in early-maturing mandarins that funding programs. One is for projects that will lead directly to the would be available on the market from O development of commercial products, tools or recommendations (Commercial November to January. Other important Product Development Committee, CPDC-18). The other is for projects with traits include cold hardiness and seed- broader, fundamental researchable questions (Research Management Committee, less varieties that are uniformly small RMC-18). Both of these funding programs have the goal to improve citrus pro- to moderate in size, attractive, sweet, duction and mitigate the effects of pests and diseases, mainly HLB. and easy to peel. The priority categories for research were established following extensive consultations with growers, researchers and other citrus industry stakeholders to identify ideas that will provide solutions to HLB and other important citrus diseases and pests, such as citrus black spot (CBS), postbloom fruit drop (PFD) and citrus nematodes. Both CPDC-18 and RMC-18 have research priorities within five categories: bactericide research, Asian citrus psyllid research, plant improvement, horticultural practices and research on other important pests and diseases affecting the citrus industry. Bactericide project research priorities aim to identify and test bactericides and delivery strategies that improve tree health and fruit quality of young and mature trees. Also included is examination of the dynamics of chemical movement within the vascular system of the tree to improve bactericide efficacy. Psyllid research priorities focus on developing new or improved strategies for psyllid Figure 3. Owari is a satsuma variety management along with examining the impact of bactericides on the psyllid, suitable for North Florida production. effects on transmission of the HLB bacterium and effects of repeated feeding and inoculation on tree health. Plant improvement research priorities focus on testing Satsumas existing varieties and developing and testing new varieties, including varieties Brown Select is the satsuma variety developed using biotechnology. Horticultural practices priorities address the that produces the largest tree and fruit effect of nutritional treatments on mitigating tree decline, including the effect of size. It has a higher yield than Owari micronutrients and macronutrients on root health. Plant growth regulators and the and matures in early November. effect of other chemicals or horticultural practices on tree health are also included Owari (Figure 3) is the most pop- in these research priorities. Other citrus diseases are also covered under the ular satsuma variety. It produces a research priorities, including citrus canker, PFD and CBS. consistent crop of small to medium- On April 25, a call for preproposals and guidelines for both funding pro- sized fruit. It reaches optimum matu- grams went out to researchers. On May 21, preproposals were due for both rity in mid-November. CPDC-18 and RMC-18. Preproposals are short descriptions of the projects that Xie Shan is an early-maturing sat- researchers plan to propose. suma variety that matures during late In early June, a panel of independent scientific experts, CRDF committees October. In previous years, Xie Shan and the CRDF board of directors will review preproposals, and recommenda- has produced large, puffy fruit that tions will be made on which projects should be invited to be developed into full were not suitable for marketing. In proposals. Full proposals will be due on July 20. They will be reviewed again by 2016, a heavy crop (300 pounds/tree) a panel of experts, CRDF committees and the board, and recommendations will of sweet, moderate-sized fruit was pro- be given on top projects to be funded. duced. In 2017, crop load was light and New research projects will be funded in early October 2018. CRDF is look- most fruit were large and puffy. More ing forward to seeing new ideas from researchers in this year’s funding cycle. observations are needed on this variety To see the complete list of research priorities and for more information, visit the before a recommendation can be made. CRDF website (www.citrusrdf.org). For more details on the perfor- Prepared by the CRDF project management team mance of satsumas in North Florida, see EDIS publication HS195, “The Satsuma Mandarin,” at http://edis.ifas. ufl.edu. Other Citrus Early Pride is a low-seeded Fallglo- Column sponsored by the Citrus Research and Development Foundation like fruit. The fruit-maturing period is Citrus Industry June 2018 17 September and October, a time when little other fresh-market citrus is avail- able in North Florida. It produces a high-quality, medium-sized fruit with good flavor that is easy to peel. Early Pride appears to be somewhat resistant to Alternaria and citrus scab. It is not cold hardy, and should only be consid- ered for the best sites that are sheltered from north winds. Early Pride should be supplied with microsprinkler irriga- tion for freeze protection. Minneola Honeybell: Minneola is an older cultivar that produces an attractive, medium-large, bell-shaped fruit. It appears to be less cold hardy than LB8-9 (Sugar Belle®) and has a later maturation (late December to January). Minneola is very susceptible to Alternaria fungus, and a rigorous spray program is required for commer- Figure 5. Population dynamic of the Asian citrus psyllid in Franklin County, Florida, during cial production. summer 2017 and winter 2018. Navel has performed very well. There have been no reported problems with Alternaria or citrus scab. Navel contain many seeds when grown in bell-shaped and high in sugar. Fruit can trees seem to be fairly cold hardy and a mixed block. It appears to be mod- have quite a few seeds when grown in a should be under consideration for erately cold hardy and matures from mixed block with citrus that can serve North Florida.