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Controlling Rhizoctonia Root Rot in Bedding Plants


Academic year: 2022

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Controlling Rhizoctonia Root Rot in Bedding Plants

Item Type text; Article

Authors Mahato, Tilak; Olsen, Mary; Schuch, Ursula K.

Publisher College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ)

Journal Turfgrass, Landscape and Urban IPM Research Summary Download date 22/03/2022 02:59:20

Link to Item http://hdl.handle.net/10150/216551



This is a part of the University of Arizona College of Agriculture 2004 Turfgrass and Ornamental Research Report, index at:


Controlling Rhizoctonia Root Rot in Bedding Plants

Tilak Mahato, Mary Olsen and Ursula K. Schuch Department of Plant Sciences and Division of Plant Pathology

University of Arizona, Tucson, AZ 85721


Rhizoctonia root rot is caused by a soil borne fungus, Rhizoctonia solani and is a serious problem in bedding plants. The objective of this study was to determine the efficacy of three chemical and two biological products for controlling Rhizoctonia root rot in cool season and warm season bedding plants.

Experiments were conducted with summer and winter bedding plants in a nursery production and landscape situation. The efficacy of conventional fungicides or biological products to control Rhizoctonia root rot in bedding plant production and simulated landscape growth cannot be evaluated from results of this study because of low mortality of plants.


Rhizoctonia root rot is caused by a soil borne fungus, Rhizoctonia solani. Rhizoctonia root rot is a serious disease worldwide, and the fungus has a wide host range. R. solani has long been recognized as a destructive pathogen to ornamentals including both cool weather bedding plants such as snapdragons and petunia, as well as warm weather plants such as vinca. Growers in nursery production rely on chemical fungicides to suppress Rhizoctonia root rot and maintain the quality of plants that are required by the market. However, very few fungicides provide acceptable control for Rhizoctonia root rot. Some biological agents are available for the control of Rhizoctonia root rot and provide a safer and environmentally friendly alternative.

The objective of this study was to determine the efficacy of three chemical and two biological products for controlling Rhizoctonia root rot in cool season and warm season bedding plants. Results of these trials could be useful to growers as a resource in disease management strategies.

Materials and Methods

Four experiments were conducted during 2003 at The University of Arizona Campus Agricultural Center in Tucson in a retractable roof greenhouse. Experiments 1 and 2 were conducted in the early spring with cool season plants - three cultivars of petunia (red, white and blue) and a color mix of snapdragons. Experiments 3 and 4 were conducted in the late spring and summer with warm season plants - two cultivars of vinca, burgundy and red. Experiments 1 and 3 were designed to simulate nursery production and were grown from plugs in 6-packs; experiments 2 and 4 simulated the landscape phase and were grown in 2-gal containers.


Potting media was artificially infested with R. solani colonized barley seed according to rates determined in preliminary greenhouse trials or was left non-infested for treatment controls. Plants placed in infested substrate were considered “inoculated”. Substrate was amended or drenched with three chemical fungicides, ZeroTol, Banrot, and Abound, and two biological products, PlantShield and SoilGuard, according to manufacturer’s recommendations, or left untreated as controls. All plants were irrigated by overhead irrigation at least twice daily.

The duration of individual experiments was 5 to 8 weeks, depending on environmental conditions and plant growth rate. At the end of each experiment, plants were rated for quality based on 1=dead, 2=stunted, and 3=healthy, and dry weights of plant top growth were determined. Throughout the experiments, dying or dead plants were removed, and the cause of death was determined by plate culture in the laboratory. Data was analyzed by analysis of variance and mean comparisons were calculated as appropriate.

Results and Discussion

Disease incidence was extremely low in all four experiments. In Experiment 1, no seedlings of petunia blue and red died, and petunia white and snapdragon had less than 6% mortality among all treatments. There were no significant differences (ANOVA) among treatments for disease control. Zerotol, applied at the highest recommended rate, caused phytotoxicity in both inoculated and non-inoculated plants. Dry weights were reduced up to 50%, and quality ratings of all cultivars were significantly lower. Snapdragon treated with Zerotol had 9.6% mortality. In subsequent experiments, Zerotol was applied at the lowest recommended rate.

In Experiment 2 for the landscape phase, there was no mortality in petunia blue and less than 2% in the other cultivars. Snapdragon dry weight and quality were not affected by inoculation or fungicide treatments (Table 1).

Petunia red and white in infested soils had significantly lower quality ratings than the untreated control. Abound had the same rating in all three petunia varieties as the non-inoculated control (Table 1).

In Experiment 3, the nursery phase testing for warm season plants, media for each treatment was infested with a single or double amount of R. solani infested barley seed or not infested as a control. The double amount of soil inoculum resulted in mortality of only up to 3% in two treatments, and single amounts resulted in only up to 2%

mortality. Dry weight of vinca burgundy and quality of both cultivars was unaffected by inoculation and treatments.

Unexplainably, dry weight of vinca red was greater in soil infested with a single or double amount of Rhizoctonia compared to non-inoculated plants. Vinca red treated with PlantShield, SoilGuard or the non-inoculated control had significantly greater dry weights than plants treated with Abound, Banrot, or Zerotol.

The landscape phase evaluating treatments for warm season plants had also low disease mortality with maximum 2.5% of inoculated vinca burgundy plants and no mortality of vinca red. Dry weight of inoculated vinca red plants was lower than that of plants in infested substrate (Table 2). Dry weight of vinca burgundy was greater for untreated control and zerotol than all other treatments, except for PlantShield, which was not different from control or any other treatment (Table 2).

In summary, based on the results of the four experiments, the efficacy of conventional fungicides or biological products to control Rhizoctonia root rot in bedding plant production and simulated landscape growth cannot be evaluated from results of this study. Plants in these experiments were irrigated consistently and fertilized sufficiently and were never under stress conditions. It is possible that more stressful growing environments, such as pronounced wetting and drying cycles that have been observed in bedding plant landscapes, may have provided conditions more conducive to Rhizoctonia causing greater mortality.


Table 1. Effect of different treatments to control Rhizoctonia on dry weight and quality rating of petunia and snapdragon growing in 2-gal. containers.

Treatment Petunia blue Petunia red Petunia white Snapdragon mix

Dry weight (g)

Abound 24.0 ab* 21.7 abc 20.3 ab 24.6 a

Banrot 20.4 b 23.2 ab 17.8 abc 26.7 a

Plant Shield 21.0 ab 20.1 bcd 16.1 c 21.9 a

Soil Gard 22.7 ab 22.0 abc 17.0 bc 17.1 a

Zerotol 21.4 b 17.1 d 16.7 bc 22.1 a

Control + inoculated 25.5 a 19.0 cd 15.9 c 19.8 a

Control non- inoculated

25.6 a 24.2 a 21.3 a 23.7 a

Quality rating

Abound 2.9 a 2.8 a 2.9 a 2.9 a

Banrot 2.2 b 2.5 b 2.2 b 2.8 a

Plant Shield 2.2 b 2.3 cd 2.0 b 2.7 a

Soil Gard 2.3 b 2.2 cd 2.1 b 2.6 a

Zerotol 2.1 b 2.0 d 2.1 b 2.9 a

Control + inoculated 2.3 b 2.1 cd 2.0 b 2.7 a

Control non- inoculated

2.8 a 2.9 a 2.8 a 2.7 a

Mortality (%)

Abound 0 0 0 0

Banrot 0 0 0 0

Plant Shield 0 0 1.7 0.8

Soil Gard 0 0 0 0

Zerotol 0 0.8 1.7 0

Control + inoculated 0 0 1.7 0

Control non- inoculated

0 0 0 0

* Means within a column followed by different letters are different at P<0.05, means separation by Tukey’s.


Table 2. Effect of different treatments to control Rhizoctonia on dry weight and quality rating of two vinca cultivars growing in 2-gal. containers.

Treatment Vinca burgundy Vinca red Vinca burgundy Vinca red

Dry weight (g) Quality rating

Abound 24.4 b 45.7 a 2.2 a 2.8 a

Banrot 25.2 b 47.7 a 2.3 a 2.8 a

Plant Shield 29.3 ab 46.0 a 2.5 a 2.9 a

Soil Gard 27.4 b 48.0 a 2.5 a 2.9 a

Zerotol 35.0 a 49.0 a 2.5 a 2.9 a

Control 30.7 a 47.2 a 2.5 a 2.8 a


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