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University of Florida, IFAS,
Central Florida Research and Education Center - Apopka
CFREC-Apopka Research Report, RH-92-8
A.R. Chase and T.A. Mellich *
Fungicides have continued to be an integral part of preventative control of Rhizoctonia diseases on most ornamental crops. New fungicides whose activity ranges are not currently known continue to become available for testing on ornamental crops. In addition, tests designed to expand labels of registered fungicides are part of the CFREC-Apopka fungicide research program. The diseases caused by Rhizoctonia solani which were included in 1991 and 1992 tests were foot rot and petiole blight of pothos, damping-off of spathiphyllum and china doll seedlings, stem rot of vinca, leaf and stem rot of Liatris sp. and aerial blight of Boston fern.
Materials and Methods
Four tests were conducted with drench applications of pentachloronitrobenzene formulations (PCNB - Terraclor 75WP at 4 and 8 oz per 100 gal and Terraclor 4F at 6, 12 and 24 oz per 100 gal), and triflumizole (Terraguard 50WP at 4 and 8 oz per 100 gal). These tests also included water sprayed inoculated and noninoculated controls. In addition, one test included benomyl (Benlate 50WP at 16 oz per 100 gal) and another test included the combination product of thiophanate methyl and mancozeb (Zyban 75WP at 24 oz per 100 gal). In the China doll (Radermachera sinica) test, treatments were applied on 9 January 1992. In the spathiphyllum (Spathiphyllum 'Gretchen') test, treatments were applied 6, 12, and 26 November 1991. In the pothos (Epipremnum aureum) test, treatments were applied 22 August and 5 September 1991. In the vinca (Catharanthus roseus) test, treatments were applied 19 September and 3 October 1991. Liatris sp. were treated on 11 and 25 March 1991. China doll plants were inoculated with R. solani AG4 (87-265) on 10 January and the percentage of damped-off seedlings was recorded on 17 January 1992. Spathiphyllum plants were inoculated with R. solani AG4 (87268) on 7 February and the number of dead leaves per plant was recorded on 4 March 1992. Pothos plants were inoculated with R. solani AG4 (84-12) on 26 August and the number of dead leaves per plant was recorded on 10 September 1991. Vinca plants were inoculated with R. solani (89-151) on 23 September and the number of dead leaves per plant was recorded on 11 October 1991. Liatris were inoculated with R. solani (89-113) on 9 March and plant height and severity of symptoms on the foliage were recorded on 30 March 1992.
The final test was performed with Boston fern (Nephrolepis exaltata). Treatments included water sprayed controls (noninoculated and inoculated), chlorothalonil (Daconil 2787 90WDG at 20 oz per 100 gal), captan (Captan 50WP at 24 oz per 100 gal), benomyl (Benlate SOWP at 16 oz per 100 gal), mancozeb (Manzate 200 80WP at 24 oz per 100 gal), the combination product of thiophanate methyl and mancozeb (Zyban 75WP at 24 oz per 100 gal), and three rates of a quaternary ammonium product (Greenshield at 1, 2, and 4 oz per 100 gal). All treatments except for Greenshield were applied on 16, 23, and 30 September 1991. Greenshield treatments were applied daily from 16 September to 6 October 1991. Boston ferns were inoculated with R. solani AG4 (84-12) on 16 September and the percentage of the foliage with aerial blight symptoms was recorded on 7 October 1991.
Results and Discussion
Excellent control of damping-off of china doll was achieved with all of the rates and formulations of Terraclor and with both rates of Terraguard (Table 1). The same treatments did not provide as high a degree of control of damping-off on spathiphyllum. In this test, best control was achieved with the lower rates of Terraclor and both rates of Terraguard. The higher rates of Terraclor formulations were associated with a slightly higher level of disease which may have been due to a slight phytotoxicity reaction (Table 1). Zyban was employed in the pothos test and provided excellent control of petiole rot as did all of the Terraclor and Terraguard treatments (Table 1). Control of Rhizoctonia stem rot on vinca was best with Benlate 50WP, but also was excellent with Terraguard (Table 1). The higher rates of Terraclor 75WP and 4F gave very good disease control. Rhizoctonia leaf and stem rot of Liatris sp. was effectively controlled with all fungicides tested with the lower rate of Terraguard (4 oz per 100 gal) and the intermediate rate of Terraclor 4F (12 oz per 100 gal) being least effective (Fig. 1). The height of the inoculated control plants was only about half that of the noninoculated control plants and all of the fungicide treated plants. This indicates that even though disease control was not as high with some of the fungicides, the plant achieved a normal height in the test period.
The final test for control of Rhizoctonia aerial blight of Boston fern showed excellent control with Daconil 2787, Benlate 50WP, and Zyban and good control with Captan (Fig. 2). Manzate and Greenshield did not provide as high a degree of control and Greenshield caused severe foliar burning and especially at the 4 oz per 100 gal rate (Fig. 2).
Both formulations of Terraclor provided good control of these Rhizoctonia diseases of ornamentals. The higher rates proved beneficial on some plants but may have resulted in slight phytotoxicity on spathiphyllum. No discernible differences between the two formulations were noted. Terraguard is now labeled for Cylindrocladium root and petiole rot of spathiphyllum. These tests show that it is also an excellent choice for Rhizoctonia control with the 4 oz per 100 gal rate as effective as the higher rate. Daconil has been shown effective in controlling aerial blight of Boston fern in the past. These tests also showed that Zyban could give a very high degree of control when used on Boston fern. Zyban is a combination of the active ingredient in Manzate (mancozeb) and thiophanate methyl (active ingredient in Cleary's 3336, Domain, and Systec). Since Manzate did not give a high degree of control, the active portion in Zyban is probably the thiophanate methyl. Further tests with thiophanate methyl compounds are planned.
*professor of Plant Pathology and Biological Scientist, respectively. Central Florida Research and Education Center - Apopka, 2807 Binion Road, Apopka, FL 32703-8504.
Table 1. Effect of Terraclor 75WP, Terraclor 4F, Terraguard 50WP, Zyban 75%WP and Benlate 50WP on severity of Rhizoctonia diseases of four ornamentals.
no. dead leavesc
no. dead leavese
|Noninoculated||---||0 af||0.4 ab||0 a||0 a|
|Inoculated||---||88.8 b||2.7 d||5.9 b||10.8 d|
|Terraclor 75WP||4||1.7 a||1.7 abcd||0 a||6.4 c|
|Terraclor 75WP||8||0.2 a||2.2 cd||0 a||2.3 ab|
|Terraclor 4F||6||0.2 a||1.8 bcd||1.0 a||5.0 bc|
|Terraclor 4F||12||0.4 a||2.8 d||0.1 a||2.1 ab|
|Terraclor 4F||24||0 a||1.6 abcd||0 a||ntg|
|Terraguard 50WP||4||1.6 a||1.2 abc||0.6 a||0.8 a|
|Terraguard 50WP||8||0.8 a||0.3 a||0 a||1.0 a|
|Zyban 75WP||24||nt||nt||1.0 a||nt|
|Benlate 50WP||16||nt||nt||nt||0 a|
a In the china doll test, treatments were applied
on 9 January 1992. In the spathiphyllum test, treatments were
applied 6, 12, and 26 February 1992. In the pothos, treatments
were applied 22 August, and 5 September 1991. In the vinca test,
treatments were applied 19 September and 3 October 1991.
b China doll plants were inoculated on 10 January and the percentage of plants that damped-off (d.o.) was recorded on 17 January 1992.
c Spathiphyllum plants were inoculated on 7 February and the number of dead leaves per plant was recorded on 4 March 1992.
d Pothos plants were inoculated on 26 August and the number of dead leaves per plant was recorded on 10 September 1991.
e Vinca plants were inoculated on 23 September and the number of dead leaves per plant was recorded on 11 October 1991.
f Means in the same column followed by a different letter were statistically different (DNMRT, P = 0.05).
g Not tested.
Figure 1. Effect of various fungicides on severity of
Rhizoctonia leaf and stem rot of Liatris sp. caused by R.
solani. Disease was rated on the following scale: 0 = no
symptoms, 1 = slight, 2 = moderate, 3 = high, and 4 = dead.
Click image for larger view.
Figure 2. Effect of various fungicides on severity of
Rhizoctonia aerial blight of Boston fern (Nephrolepis exaltata)
caused by R. solani.
Click image for larger view.
by Don Short,
University of Florida
Important notice: According to the Federal Insecticide, Fungicide and Rodenticide Act as amended, all pesticides must be handled and applied in strict accordance with directions on the pesticide container label. The plant and pest must be listed on the label. Also, if a pesticide is used inside the greenhouse, it must be labeled for greenhouse use. To the best of our knowledge, the suggested pesticides listed in UF/IFAS publications are labeled for controlling the specific pests discussed. However, pesticide labels differ widely in plant and insect listings. Some are broad ornamental labels and others specifically list certain plants and species of pests for which the pesticide is labeled. Read the label carefully.