OIL SPOTTING (OLEOCELLOSIS) OF CITRUS FRUIT W. F. Wardowski, A. A. McComack, and W. Grierson' WHAT IS OIL SPOTTING? Oil spotting (illustrated on the cover of this circular) is a common peel injury of citrus fruit, usually caused by mechanical damage.2 It causes extensive financial loss to growers, shippers, and handlers, not only in Florida but everywhere in the world, particularly in the more humid areas where citrus fruit are grown for the fresh fruit market. Oil spotting is also known as: oleocellosis, oleo, bruising, green spot, and, erroneously, as "gas burn." It can occur at any time 1Associate Horticulturist, Cooperative Extension Service; Food Technol- ogist, Florida Department of Citrus; and Horticulturist, University of Florida, respectively, all located at the Agricultural Research and Edu- cation.Center, Lake Alfred sa880. 2Cooperative research by the University of Florida and the Florida De- partment of Citrus. during harvesting, handling, and marketing, but it mostly occurs at or near harvest. Mechanical injury forces the toxic oil out of the epidermal oil glands. The oil kills adjacent cells of the flavedo. Citrus peel oil from injured fruit can also cause oil spotting on the surface of adjacent undamaged fruit. Fresh oil spotting is barely visible. With time, the damaged areas will sink and darken, causing the oil glands to remain prominent. Symptoms may be seen as the fruit arrive at the packinghouse, but are often not noticed until after degreening or shipment. Cells killed by oil are readily invaded by fungi re- sulting in increased decay. WHAT WE KNOW ABOUT OIL SPOTTING Oil spotting can be reduced or eliminated on susceptible crops by good handling practices. Susceptible Varieties All types and varieties of citrus can suffer damage from oleo- cellosis, but those with numerous, prominent oil cells are partic- ularly vulnerable. Oleocellosis occurs on all varieties of citrus, but in Florida it is most severe on 'Parson Brown' and 'Navel' oranges, grapefruit, 'Temples', tangelos, tangerines, lemons, and limes. Turgid and Small Fruit Turgid fruit, particularly when harvested under foggy, wet, or humid conditions, are most likely to develop oil spotting. Small sizes tend to be more susceptible to oil spotting than large sizes. Time of Day Fruit turgidity is greatest, and hence the danger of oil spot- ting is most serious, early in the morning. It is particularly hazardous to pick susceptible crops when the dew is still on them. Ethylene Degreening Ethylene does not cause oil spotting, and "gas burn" is a ter used without justification. However, the delay while fruit a: degreening allows the oil spotting to darken, making it easier see. Oil spots will darken less when fruit are held in high, rath, than low, humidity before washing and waxing. The affect areas on green fruit will not degree with ethylene, but rema as green, grade-lowering blemishes. Color-Add The color-add process does not cause oil spotting. However, tl color-add dye preferentially stains the injured areas, makir them more obvious. THE IMPORTANCE OF OIL SPOTTING Losses from oil spotting are common and have increased i recent years due to rough handling during harvest. Fruit ha vested for the fresh fruit market, handled through the packing house, and then sent to the processor as "eliminations" invoh an economic loss. Packed fruit subsequently rejected by tl wholesale buyer or retail consumer represent even greater losse OIL SPOTTING CAN BE REDUCED OR ELIMINATE[ Oil spotting can be avoided or greatly minimized if a ft simple rules are followed. *Require pickers to handle fruit carefully, particularly tend specialty varieties. Avoid cannery crews who are accustomed handling fruit roughly. *Pick dry fruit. Avoid harvesting when fruit are wet fro dew, fog, rain, or irrigation, particularly early in the morning *Use a pressure tester as a guide to determine when a crop likely to suffer ruptured oil cells, causing oil spotting. A press tester is absolutely necessary to judge when to harvest lemor where a rule of thumb (using a %/ inch cylindrical tip) is: wh less than 3 pounds of pressure ruptures oil cells, harvest is ii possible; 3 to 7 pounds, harvest with extreme caution; over pounds, harvest like other citrus varieties.