Greasy spot is usually more severe on leaves of grapefruit, Pineapple, Hamlins and tangelos than on Valencias, Temples, Murcotts, and most tangerines and their hybrids. Airborne ascospores produced in decomposing leaf litter on the grove floor are the primary source of inoculum for greasy spot. Internal growth is slow and symptoms do not appear for several months. Warm humid nights and high rainfall, typical of Florida summers, favor infection and disease development. Major ascospore release usually occurs from April to July with favorable conditions for infection occurring from June through September.
Leaves are susceptible once they are fully expanded and remain susceptible throughout their life.
Trilogy may be substituted for petroleum oil when used with copper but is not effective when used alone. With average quality copper products, 2-4 lb of metallic copper per acre usually provide adequate control. On early and mid-season oranges and grapefruit for processing, two sprays may be needed especially in the southern part of the state where warmer winter temperatures promote earlier defoliation. Two applications may be needed also where severe defoliation from greasy spot occurred in the previous year. In those cases, the first spray should be applied in June and the second in August.