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Relationship of Potassium to a Leaf Spot of Ficus elastica ‘Decora’. Robert B. Marlatt, Associate Plant Pathologist, University of Florida, Subtropical Experiment Station, Homestead 33030; Paul G. Orth, Assistant Soils Chemist, University of Florida, Subtropical Experiment Station, Homestead 33030. Phytopathology 60:255-257. Accepted for publication 3 September 1969. DOI: 10.1094/Phyto-60-255.

Ficus elastica ‘Decora’, an important commercial crop in southeastern Florida, has a severe spotting of the undersides of leaves with which no pathogenic organism has been associated. Low K and high Mg increased the disease, but an imbalance of B, Ca, Cu, Fe, Mn, Mo, or Zn did not produce these symptoms. Disease was greatly diminished by a hydroponic solution containing a high concentration of K.