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Effects of Potting Medium pH and Air Temperature on Severity of Cylindrocladium Root and Petiole Rot of Spathiphyllum sp.. A. R. Chase, Associate Professor of Plant Pathology, University of Florida, IFAS, Agricultural Research and Education Center, Apopka 32703. R. T. Poole, Professor of Ornamental Horticulture, University of Florida, IFAS, Agricultural Research and Education Center, Apopka 32703. Plant Dis. 71:509-511. Accepted for publication 27 November 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0509.

Incorporations of dolomitic lime affected both potting medium pH and development of Cylindrocladium root and petiole rot of Spathiphyllum spp. During the fall, winter, and spring, plants grown with little or no added dolomite had more severe disease levels than plants grown with high levels of dolomite in the potting medium. Addition of dolomite at rates of 2.49.6 kg/m3 of a Canadian peat-pine bark potting medium (50:50) resulted in a pH range of pot leachates of about 4.0 (no dolomite added) to 7.0 (9.6 kg/m3). Efficacy of benomyl was not affected by these levels of dolomite. Although the same pH range was established in summer tests, disease severity was not affected. In similar tests employing MgSO4 and CaSO4, increased amounts of these compounds did not affect pH of pot leachate or disease severity. Although disease severity was affected by air temperature, there was no significant interaction between air temperature and pH. An interaction between temperature and pH was found for in vitro growth of Cylindrocladium spathiphylli, with poorest growth at pH 4.0 and incubation temperature of 32 C.