Fungicides such as the thiophanate methyl compounds (Cleary, Domain, Fungo, Topsin M, and Zyban [thiophanate methyl and mancozeb]) provide excellent control of Rhizoctonia diseases on a wide variety of potted ornamentals. Terraclor and Terraguard have been found to work very well on some plants but to a lesser degree on others whether symptoms involved roots, stems or leaves of plants. Chipco 26019 also gave excellent disease control which was a little better on aerial diseases than stem and root diseases. Comparisons of these fungicides to Benlate indicate that on many plants affected by Rhizoctonia spp. a number of highly effective alternatives are available.

Fungicides continue to be an integral part of preventative control of Rhizoctonia diseases on many ornamental crops. Although Rhizoctonia spp. are soilborne fungi, they do not always cause root diseases. Aerial blight caused by R. solani is the most common symptom on Boston fern, while stem rot is the most common symptom on impatiens and poinsettias. This makes the application site for the fungicides critical since soil drenches are more effective in controlling root diseases and foliar sprays are more effective in controlling stem rots and aerial blights.

A review of the literature of ornamental potted crops reveals a wide variety of fungicides which are effective against Rhizoctonia spp. In general, the root and basal stem diseases are better controlled when the fungicide is applied to the soil as can be seen with the Rhizoctonia crown or stem rot on poinsettia (Benson, 1991 and Powell, 1988). In this case, a Terraclor drench was very effective while the same compound applied as a spray was significantly less effective. A similar situation developed when Benlate was used to control aerial blight of Boston fern (Chase, 1988). When this compound is used as a spray, excellent disease control occurs but when used as a drench, disease control is reduced. Best control of impatiens crown (stem) rot was achieved with drenches of a number of fungicides including thiophanate methyl compounds (Domain, Fungo and Topsin M) as well as Benlate, Chipco 26019 and Terraclor (Castillo and Peterson, 1990; Chase and Mellich, 1992 and Chase, 1993). Binucleate Rhizoctonias are the cause of aerial blight on pittosporum and azalea. The aerial blight on pittosporum was best controlled with either a Benlate or Domain spray while Terraneb gave no control (Chase and Stamps, 1992). Terraneb did give excellent control of aerial blight on Boston fern which is caused by R. solani. Control of the binucleate Rhizoctonia on azalea was excellent with Chipco 26019 drenches in some tests and only good in others (Frisina, 1988). Variable results from one trial to the next can be common since environmental conditions cannot be completely controlled. Table 1 summarizes the literature review of fungicides for Rhizoctonia control on ornamentals.

Many of the fungicides were tested on a variety of ornamentals. In most tests with thiophanate methyl compounds (Cleary, Domain, Fungo, Topsin M and Zyban [thiophanate methyl and mancozeb]) excellent disease control was achieved. Results were usually as good as those achieved when Benlate was used. Terraclor and Terraguard have been found to work very well on some plants but to a lesser degree on others whether symptoms were of an aerial or basal type. Most trials with Chipco 26019 showed a similar pattern with perhaps more control of aerial diseases than basal stem and root diseases.

Comparisons of these fungicides to Benlate indicate that on many plants affected by Rhizoctonia spp. a number of highly effective alternatives are available. Be sure to read labels to check for legal uses and perform phytotoxicity trials on a small group of plants when you are trying a new fungicide.

Benson, D. M. 1991. Control of Rhizoctonia stem rot of poinsettia during propagation with fungicides that prevent colonization of rooting cubes by Rhizoctonia solani. Plant Disease 75:394-398.

Castillo, S. and J. L. Peterson. 1990. Cause and control of crown rot of New Guinea Impatiens. Plant Disease 74:77-79.

Chase, A. R. 1988. Boston Fern (Nephrolepis exaltata cv. Compacta) aerial blight of Rhizoctonia solani AG4. Fungicide & Nematicide Tests 43:288-289.

Chase A. R. 1988. New fungicides or fungicide uses for foliage plants - 1988. Proceedings of the 4th Conference on Insect and Disease Management on Ornamentals. Society of American Florists. pp. 148-152.

Chase, A. R. 1988. Fungicides for control of leaf spots of foliage plants - 1988. Central Florida Research and Education Center, Univ. of Fl., CFREC-Apopka Research Report RH-88-14.

Chase, A. R. 1989. Fungicide trials for Cylindrocladium, Helminthosporium, Pythium and Rhizoctonia diseases of ornamentals - 1989. Central Florida Research and Education Center - Univ. of Fl., CFREC-Apopka Research Report RH-89-15.

Chase, A. R. 1990. 1990 fungicide trials for control of Alternaria, Helminthosporium, Phytophthora and Rhizoctonia diseases of ornamentals. Central Florida Research and Education Center, Univ. of FL., CFREC-Apopka Research Report RH-90-25. Chase, A. R. 1993. Fungicides to replace Benlate for some diseases of ornamentals. Central Florida Research and Education Center, Univ. of Fl., CFREC-Apopka Research Report, RH-93-1.

Chase, A. R. and T. A. Mellich. 1992. Controlling Rhizoctonia diseases on ornamentals with fungicides. Central Florida Research and Education Center, Univ. of Fl., CFREC-Apopka Research Report, RH-92-8.

Chase, A. R. and R. H. Stamps. 1992. Fungicides for control of Rhizoctonia aerial blight. Cut Foliage Grower 7(11/12):1-3.

Frisina, T. A. and D. M. Benson. 1988. Sensitivity of binucleate Rhizoctonia spp. and R. solani to selected fungicide's in vitro and on azalea under greenhouse conditions. Plant Disease 72:303-306.

Powell, C. C., Jr. 1988. The safety and efficacy of fungicides for use in Rhizoctonia crown rot control of directly potted unrooted poinsettia cuttings. Plant Disease 72:693-695.

Stephens, C. T. and T. C. Stebbins. 1985. Control of damping-off pathogens in soilless container media. Plant Disease 69:494-496.