Problems in controlling Phytophthora cactorum on cattleya orchids

Robert T. McMillan, Aaron Palmateer, Robert A. Cating


The major fungus on cattleya orchids in Florida and in the New and Old World countries is Phytophthora cactorum (Lebert & Cohn) J. Schroet. and Phytophthora palmivora, which causes black rot of leaf and heart rot during the cooler months of the year. All species of cattleya and their interspecific and intergeneric hybrids are susceptible. Phytophthora cactorum infects leaves, pseudobulbs, rhizomes, and flower buds. Recovery studies of infected plants that involved cutting out the infected tissue were found not to be effective, even with treatments of fungicides such as Banrot, Natriphene, Shield Brite, Truban, and Phyton 27. A second study of fungicide sprays and drenches of Banrot, Heritage, Shield Brite, Stature, Truban, Pentathlon, Aliette, Subdue Maxx, and Insignia for the control of phytophthora-infected leaves, pseudobulbs, and rhizomes was conducted from 2005 to 2008. The fungicides Aliette, Insignia, Stature, and Subdue Maxx, when applied as preventive sprays, were found to be significantly effective for the control of cattleya leaf and flower bud infection. However, Aliette was only effective for control of P. cactorum when applied to leaves that were in the receptive stage. The fungicides Aliette, Banrot, Heritage, Insignia, Shield Brite, Stature, Subdue Maxx, and Truban, when applied as preventive drench, were found to be significantly effective for the control of P. cactorum in community pots of cattleya seedlings.


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Proc. Fla. State Hort. Soc.     ISSN 0886-7283