Control of Cylindrocladium Root Rot of Spathiphyllum with Fungicide Drenches

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D. J. Norman, Ph.D.*

University of Florida
Institute of Food and Agricultural Sciences
Central Florida Research and Education Center

CFREC-Apopka Research Report RH-96-6

During the warm summer months, Cylindrocladium spathiphylli can cause severe damage to Spathiphyllum. Chlorotic lower leaves and a wilted appearance are usually the first symptoms observed; however, these symptoms are secondary and brought on by extensive root damage caused by this pathogen. If newly infected roots are examined, reddish-brown lesions can be found. These lesions grow rapidly causing total root collapse and rot. Thousands of spores are produced within these infected root masses for future disease spread.

Cylindrocladium spores are moved from plant to plant via water; therefore, plants should never be set directly on the floor of a production facility. Large Spathiphyllum plants should be placed on benches or, at a minimum, on inverted saucers so that roots and soil do not come in contact with contaminated water. If spores are splashed onto leaves, dime sized circular brown necrotic lesions surrounded by yellow halos will eventually form. When infections are detected in a production facility, plants showing severe symptoms should be removed and remaining plants should be drenched with an appropriate fungicide.

This study was undertaken to examine the efficacy of five fungicides for the control of Cylindrocladiurn root rot. The fungicides used in this study were: 1) Cleary's 3336®-F (thiophanate-methyl, 20 oz/100 gal); 2) fluazinam (ISK Biosciences product currently not labeled for ornamentals, 6 oz/100 gal and 12 oz/100 gal); 3) Phyton 27® (copper-sulfate pentahydrate, 2 oz/10 gal and 3.5 oz/10 gal); 4) Terraguard® 50W (triflumizole, 4 oz/100 gal and 8 oz/100 gal); and 5) Terraneb® SP (chloroneb, 3 lb/50 gal and 6 lb/50 gal). Two control treatments were also utilized: 1) Noninoculated control where no fungus or fungicide was applied; and 2) an inoculated (positive) control, where fungal spores were applied without any applications of fungicide. The experiment was set-up in a randomized complete block design with ten plants for each of the eleven treatments. Spathiphyllum 'Petite' plants were utilized in this study. Plants were transferred from 72-plug cell packs and planted in 4" pots (450 cm²) containing Vergo Container Mix A (Verlite Company, Tampa, FL 33610) amended with Sierra Plus Minors 17N-6P-12K (Scotts, 1001 Yosemite Dr., Milpitas, CA 95035) at the rate of 1.5 g per pot. Plants were kept in a fiberglass house maintained between 60 and 90°F, with a maximum light level of 190 µmol·m^-2·s^-1 (1000 ft-c).

Two months after potting plants, fungicide treatments were applied as a drench (100 ml/pot). One week later, plants were inoculated with Cylindrocladium spores. Fungal spores were harvested from cultures grown on potato dextrose agar into sterile distilled water. Spore concentrations were adjusted with the aid of a hemacytometer to 1 X 104 spores/ml and 5 ml (50,000 spores) was applied to each plant. Chemical drenches were continued at two week intervals for a total of four applications. Three weeks after inoculation and weekly thereafter, disease severity on individual plants was visually estimated. The final visual rating was done two weeks after the last drench. For statistical purposes, percentage of individual plants having wilted, clorotic and necrotic leaves was ranked using a pretransformed rating scale (Little and Hills, 1978) as follows: 0 = no symptoms; 1 = 1-10%; 2 = 11-35%; 3 = 36-65%, 4 = 6690%, 5 = 91-100%. Results from the eleven treatments were compared statistically to determine if significant differences occurred in the experiment using Tukey's LSD procedures.

Conclusions

Under the environmental conditions in this study and with high disease pressure, there are no chemicals which provided complete protection from infection. However, Cleary's 3336® (20 oz/100 gal), fluazinam (12 oz/100 gal), and Terraguard® 50W (4 oz and 8 oz/100 gal) kept disease severity ratings below 1.5 (Table 1). No statistical differences were observed between these four treatments (Table 1). In this study, Phyton 27® was not as effective as the four previously mentioned treatments; however, at the 35 oz/100 gal rate it was equal to fluazinam at 6 oz/100 gal rate and better than the inoculated control. Terraneb® and the low rate of Phyton 27® treatment, under this high disease pressure was ineffective in slowing the infection process. No disease damage was observed in the Noninoculated control plants.

The best results for fungicides tested at more than one rate were at the highest recommended rates for disease control. If fungicides are to be applied as a disease preventative precaution, lower labeled rates and intervals should be selected. It is unlikely under normal conditions that individual plants would receive 50,000 spores at one time. Therefore, high rates should be used only when disease pressure is high. If a disease outbreak occurs in a production facility, the higher rates and intervals should be selected in order to slow disease spread. When encountered, diseased plants should be removed, thus lowering inoculum in the nursery and remaining plants should be drenched. It is advisable that chemicals should be rotated to lower chances of disease resistance and to protect against possible phytotoxic reactions. No phytotoxic reactions were observed in this study from any of the compounds tested.

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*Assistant Professor of Plant Pathology, University of Florida, IFAS, Central Florida Research and Education Center, 2807 Binion Road, Apopka, FL 32703-8504.

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References

1. Little, T. M. and Hills, F.J. 1978. Agricultural Experimentation Design and Analysis. John Wiley and Sons, New York, pp 350.
2. Simone G, Elliott, M., and Mullin, R. 1994. Florida Plant Disease Control Guide, Volume 1. Plant Pathology Dept., University of Florida, Gainesville FL. 362 pp.
3. Turf & Ornamental Reference for Plant Protection Products. 1995. 4th edition, C & P Press, N.Y., 747 pp.

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1. Note: Mention of a product does not constitute a recommendation or warranty of the product by the author or the University of Florida nor does it imply its approval to the exclusion of other products. Pesticide registration may change so it is the responsibility of the user to ascertain if a pesticide is registered by the appropriate state and federal agencies for an extended use. Pesticides should be used according to label instructions and safety equipment required on the label and by federal or state law should be employed.

1. Table 1. Final disease severity rating of Cylindrocladium root-rot on Spathiphyllum plants after four chemical drenches over an eight week period. Treatments having the same letter under Tukey's LSD are not significantly different. Disease severity rated using a pretransformed rating scale: 0 = no symptoms; 1 = 1-10%; 2 = 11-35%; 3 = 36-65%, 4 = 66-90%, 5 = 91-100%.