Promising activity of pencycuron, a phenylurea-based fungicide, for effective management of black scurf of potato

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1 Indian Phytopath. 55 (1) : (2002) Promising activity of pencycuron, a phenylurea-based fungicide, for effective management of black scurf of potato T.S. THIND, CHANDER MOHAN and SWEETY KAUR Department of Plant Pathology, Punjab Agricultural University, Ludhiana ABSTRACT: Pencycuron, a phenylurea-based fungicide, caused total inhibition of mycelial growth of Rhizoctonia solani at 25 j..iglml and was found most effective in checking black scurf of potato. Its formulations monceren 250 SC and monceren 25 WP provided almost complete control of the disease when used as dip treatment at 0.5 and 0.75% concentrations under pot house and field conditions during and crop seasons. Emisan % appeared next in order of efficacy. Vitavax- 75 WP, though found to be highly inhibitory in vitro, but did not control the disease as effectively in pot house and in field. The efficacy of bavistin (0.3%) was at par with vitavax 75 WP (0.5%). Vitavax 200 WP (0.35%)appeared to be slightly more effective than vitavax 75 WP (0.25 and 0.5%). Boric acid (3%), though provided 66.5% disease control, but showed slightly adverse effect on tuber germination, plant height and yield. Kitazin (0.1 and 0.2%) proved to be least effective. Both the formulations of pencycuron did not show any adverse effect on plant growth parameters and can serve as effective and safer alternative to the hazardous mercurial fungicides for the management of black scurf of potato. Key words: Rhizoctonia solani, black scurf, potato, pencycuron, monceren, fungicides Black scurf of potato caused by Rhizoctonia solani Kuhn. although has not much direct effect on tuber yield but it reduces the market value of the produce considerably (Dutt, 1979). The disease is gaining importance in the Punjab state especially in the areas where potato crop is cultivated after rice or sunflower. Disease incidence on potato tubers varies from 5 to 60% with average of 27% in the Punjab state (Anonymous, 2000). Due to soil-borne nature of the pathogen, it is very difficult to manage it. Infected potato tubers help in the carry over of the inoculum both in time and space. Very few fungicides possess good efficacy against R. solani. Quintozene (PCNB) which had excellent activity against this pathogen has been banned due to its longer persistence and adverse effects on soil fauna. Organic mercurial compounds, notably methoxy ethyl mercury chloride (MEMC), among others, are currently being used on commercial scale for controlling black scurf. These fungicides are also being banned because of their ill effects on animals and human health (Somani, 1986; Khanna et ai., 1991). Boric acid (3%) has been recommended for its control but it is costlier over MEMC. Thus, there is strong need to search non-hazardous and equally effective alternatives to mercurial fungicides. Pencycuron is a phenylurea -based fungicide and has been recently introduced in India by Bayer (India) Ltd. It has earlier been reported to exhibit higher level of activity against R. solani in Switzerland (Kataria et ai., 1991). A study was undertaken to determine the efficacy of pencycuron and other fungicides against black scurf of potato under laboratory, pot house and field conditions with the view to find out safer and better alternative to control this disease. MATERIALS AND METHODS Experiments were conducted under laboratory, pot house and field conditions to determine in vitro and in vivo efficacy of pencycuron along with other

2 40 Indian Phytopathology [Vol. 55(1) : 2002) fungicides against black scurf of potato.the culture of R. so/ani was isolated on potato dextrose agar (PDA) from infected potato tubers of cv. Kufri Chandramukhi and maintained on PDA slants at 15 C for further study. Samples of monceren 250 SC and monceren 25 WP, each containing 25 per cent pencycuron (N-{ (4-chlorophenyl)-methyl}-N-cyclopentyl-N'- phenylurea (C.A.) were obtained from Bayer (India) Limited, Mumbai. Other fungicides tested were emisan-6 SO (6% methoxy ethyl mercury chloride), vitavax 75 WP (75% carboxin), vitavax 250 WP (37.5% carboxin % thiram) and bavistin 50 WP (50% carbendazim). In addition, kitazin 48 EC (48% edifenphos) and boric acid were also evaluated in pot house and field experiments. For laboratory evaluation, stock solutions of fungicides were prepared in sterilized distilled water based on active ingradient of the compound and further dilutions were made to the desired concentrations. While for pot house and field studies, fungicide concentrations were prepared on the formulation basis. To determine fungitoxic potential in vitro, fungicide formulations were incorporated into potato dextrose agar (PDA) medium to get concentrations of 10, 25,100, 200, 300 and 500 ijg/ml (a.i. basis) and the medium poured into 90 mm petridishes. Same concentrations of three other fungicides i.e. emisan-6 SO, vitavax 75 WP and bavistin 50 WP were also prepared and mixed in PDA for the comparison of efficacy. Untreated inoculated petridishes served as controls. After solidification of the fungicide amended medium each dish was inoculated with mycelial disc (6 mm diam.) taken from the periphery of young actively growing colony of R. so/ani. Three replications were maintained for each concentration. After incubation (25±1 C) for 7 days in darkness, radial colony diameter was measured and per cent inhibition in mycelial growth was calculated on the basis of unamended checks. Equipotent fungicide doses at the EDgO level (effective concentration causing 90 per cent growth inhibition) were determined from dose-response curves. The assay was repeated once. For determining efficacy of test fungicides against black scurf of potato under pot house conditions, naturally infected tubers of potato cv. Kufri Chandramukhi showing scurfy surface were given dip treatment for 10 minutes and air- dried under shade. Tubers dipped in water only served as control. Six tubers were taken for each treatment and were sown in 12" diam. earthen pots (2 tubers/pot) in the second week of October, 1999 and After 110 days of sowing, the tubers were harvested, the number of healthy and infected tubers were counted in each treatment and the disease severity was determined by following 0-4 rating scale (O=healthy, 1=up to 20%, 2=21-50%, 3=51-75%, 4=more than 75% surface area infected). Per cent disease control was calculated from these observations based on the disease severity in untreated check. Fungicides at different concentrations (Table 1) were further tested against potato black scurf under field conditions during and crop seasons. In addition, monceren 25 WP was also included in the study during crop season. Infected seed tubers of potato cv. Kufri Chandramukhi showing black scurf symptoms were divided into small lots of 200 tubers each and were dip-treated in solutions of respective test fungicides for 10 minutes. The treated tubers were air- dried and sown on ridges ( row to row 60 ern, tuber to tuber 15 ern, bed size 4 x 2 m) in 3 rd week of October, 1999 and 2000 and the crop was raised following standard agronomic practices. Untreated tubers sown in similar way served as control. One bed was used per replication and three replications were kept for each treatment in RBD pattern. The crop was harvested in the 3rd week of Februray and per cent incidence of black scurf on tubers was recorded by counting healthy and diseased tubers in a lot of one hundred tubers in each treatment. Disease severity was determined by using 0-4 rating scale as mentioned in pot house study. Observations on tuber germination, plant height and number of shoots in 20 randomly selected plants in each of the treatments were also recorded along with tuber yield per plot. Per cent disease control was calculated from disease severity data and the results were ana lysed statistically. RESULTS AND DISCUSSION In vitro activity against R. solani The data on colony diameter of R. so/ani at different concentrations of test fungicides and its

3 [Vol. 55(1) : 2002] growth inhibition revealed that among the four fungicides tested, monceren-250 SC showed maximum inhibitory effect and caused complete inhibition of mycelial growth of R. solani at 25 jjg/ rnl Even lower doses of this fungicide were found to be highly effective and showed only 4.5 and 1.2 mm colony diam. at 5 and 10 jjg/ml, respectively, compared to 79.5 mm diam. in untreated control. This was closely followed by vitavax-75 WP which also caused complete inhibition at 25 jjg/ml and also prooved highly effective at lower concentrations. Bavistin 50 WP and Emisan-6 appeared next in order with complete growth inhibition at 50 and 300 jjg/ml, respectively. The ED90value was also the least for monceren followed by vitavax, bavistin and emisan. Efficacy in pot house Dipping of infected tubers in suspensions of test fungicides for 10 minutes controlled the disease to varying extent. Among various treatments tried, pencycuron formulations (monceren 250 SC and monceren 25 WP) checked the black scurf incidence and severity at the two concentrations i.e. 0.5 and 0.75% during both the years of study. Both the formulations of pencycuron were equally effective and provided complete control of black scurf. Emisan-6 (0.25%), which is a recommended fungicide for black scurf control in the state, appeared to be the next best fungicide with 75.5% disease control. It was followed by boric acid (3%), vitavax 200 WP (0.7 and 0.35%), bavistin 50 WP (0.3%) and vitavax 75 WP (0.5%) providing 42.4, 41.0, 30.6, 22.3 and 21.8% disease control, respectively. Treatments with kitazin (0.1 and 0.2%) and lower concentration of boric acid (1.0%) were found least effective. Lower dose of vitavax 75 WP (0.25%) also gave inferior disease control. In untreated tubers, disease severity was 44.8 and 55.4%, respectively during the two years. Performance in field As evident from data on disease incidence and severity presented in Table 1, both the formulations of pencycuron (monceren 250 SC and monceren 25 WP) provided almost complete control (98.4 to 99.8%) of potato black scurf at the concentrations tested. The results were similar during both the years. Even at lower concentration Indian Phytopathology 41 of 0.25%, monceren 250 SC exhibited 94.26% disease control. The results of the field efficacy of monceren to control potato scurf were similar to those observed under pot house conditions. Emisan-6 (0.25%) appeared to be the next best fungicide in order of efficacy where mean disease severity of 12.8% was recorded compared to 42.7% in untreated check. It was closely followed by boric acid (3%), which provided 66.5% control of black scurf. The new formulation of vitavax tested i.e. vitavax 200 WP proved better than vitavax 75 WP in controlling black scurf, where disease control of 56.6 and 58.8% was recorded at 0.35 and 0.75% concentrations, respectively, compared to 29.8 and 51.4% control at 0.25 and 0.5% concentrations of vitavax 75 WP. Bavistin (0.3%) was found almost at par with vitavax 75 WP (0.5%) in checking this disease. Kitazin at both the concentrations of 0.1 and 0.2% was found least effective. Effect on growth parameters and tuber yield Influence of monceren and other fungicide treatments on tuber germination, plant height, number of shoots and tuber yield were recorded during field experiments and are presented in Table 2. There was no adverse effect of any of the treatments on tuber germination except boric acid (1 and 3%) where 88 and 74% germination was recorded compared to 100% germination in all other treatments including untreated control. Boric acid treatments also showed adverse effect on plant height, number of shoots per plant and tuber yield. Average plant height and number of shoots per plant were slightly more in monceren 250 SC treatments (Table 2). In the other fungicide treatments, no apparent effect was observed on these growth parameters. Tuber yield in various treatments did not show any appreciable increase comapred to untreated check. Monceren 250 SC treatments showed slightly higher yield while boric acid gave slightly lower yield compared to other fungicide treatments. The yield in various treatments varied from 8.1 kg to 9.0 kg per plot. The preceding results indicate the superior efficacy of pencycuron (monceren) among various fungicides tried in controlling black scurf of potato both under laboratory and pot house/field

4 42 Indian Phytopathology [Vol. 55(1) : 2002] Table 1. Field performance of monceren and other fungicides against black scurf of potato tubers (cv. Kufri Chadramukhi) during and crop seasons Treatments/*Dose Disease incidence (%) Disease severity (%) **Disease (%) I Year II Year Mean I year II year Mean control (%) Monceren SC 0.2 NT 8.7 (17.2) 8.7 (17.2) NT 2.4 (9.0) 2.4 (9.0) 94.2 (76.1) (5.7) 0.5 (4.0) 0.7 (4.9) 0.2 (2.8) 1.1 (1.8) 1.1 (2.3) (0.0) 0.5 (4.0) 0.2 (2.8) 0.0 (0.0) 1.1 (1.8) 0.0 (1.2) 99.8 (88.0) Monceren - 25 WP Emisan - 6 SD Bavistin - 50 WP Vitavax - 75 WP Vitavax WP Boric acid Kitazin (9.3) NT 2.6 (9.3) 0.6 (4.6) NT 0.6 (4.6) 98.4 (82.8) (4.6) NT 0.6 (4.6) 0.1 (2.2) NT 0.1 (2.2) 99.6 (86.3) (37.8) 18.6 (25.5) 28.1 (32.0) 18.6 (25.5) 7.0 (15.3) 12.8 (20.9) 69.4 (56.7) (59.0) 29.7 (33.0) 51.6 (45.9) 33.0 (35.0) 10.0 (18.4) 21.5 (27.6) 49.6 (44.7) (74.6) 53.7 (47.1) 73.3 (58.9) 41.5 (40.1) 18.3 (25.3) 29.9 (33.1) 29.8 (33.1) (54.2) 48.5 (44.1) 55.5 (48.1) 26.4 (30.9) 14.9 (22.7) 20.7 (27.0) 51.4 (45.8) 0.3 NT 55.5 (48.1) 55.5 (48.1) NT 18.5 (25.4) 18.5 (25.4) 56.6 (48.8) 0.7 NT 43.2 (41.1) 43.2 (41..1) NT 17.5 (24.7) 17.5 (24.7) 58.8 (50.1) (70.2) 65.1 (53.7) 72.3 (58.2) 35.5 (36.5) 29.5 (32.8) 32.5 (34.7) 23.8 (29.2) (45.0) 18.5 (25.4) 34.3 (35.8) 22.1 (28.0) 6.5 (14.7) 14.3 (22.2) 66.5 (54.6) (80.9) 85.3 (67.4) 91.4 (72.9) 42.2 (40.5) 30.5 (10.7) 36.3 (37.0) 14.8 (22.6) (73.5) 76.1 (60.7) 84.0 (66.4) 35.3 (36.4) 39.5 (38.9) 37.4 (37.7) 12.4 (20.6) Control 93.5 (75.2) 81.4 (64.4) 87.4 (69.2) 47.2 (43.3) 38.2 (38.1) 42.7 (40.8) CD (P = 0.05) 3.0 *Based on formulation of test fungicides used; **Based on mean of two years data; NT= Not tested; Figures in parentheses represent arcsine transformed values conditions. The superior performance of this fungicide may be attributed to its strong and specific action against R. solani and to its longer and persistent action on the pathogen (Yamda, 1986). Emisan-6 appeared to be next best fungicide in order of performance. This fungicide is currently used for controlling black scurf of potato in majority of potato growing areas in the country (Khurana et al., 2001). Mercurial fungicides, however, have been banned because of their ill effects on the environment. Boric acid was found less effective and slightly toxic in the present study, but its dip and atomised 3% has been reported to be more efficaceous in reducing black scurf of potato (Khanna and Sharma, 1996). Vitavax 75 WP, though proved highly effective against mycelial growth of R. solani in the laboratory, but it did not control the disease as effectively under pot house and field conditions. Low field efficacy of vitavax could possibly be due to its lesser. ability to penetrate and kill the hard sclerotia of the fungus on the surface of potato tubers during dip treatment for 10 minutes. Vitavax, however, has been reported to give good control of stem canker phase of the disease (Khanna et al., 1991). Vitavax 200 WP proved slightly better in efficacy than vitavax 75 WP against this disease. The other fungicides tested i.e. bavistin and kitazin appeared

5 [Vol. 55(1) : 2002] Indian Phytopathology 43 Table 2. Influence of monceren and other fungicides on tuber germination, plant height, number of shoots and tuber yield of potato (cv. Kufri Chandramukhi) under field conditions Treatments/Dose Av. tuber Av. plant (%) germination height (%) (cm) Av. number shoots/plant of Tuber (kg/plot) yield Monceren SC Monceren - 25 WP Emisan - 6 SO Bavistin - 50 WP Vitavax - 75 WP Vitavax WP Boric acid Kitazin Control CD (P=0.05) (}.O Figures are average of two years data Germination was delayed by 5 days in case of 3% Boric acid less effective in this study. Carbendazim has, however, been reported to be quite effective against this disease by Khanna et at. (1991). The. study demonstrated that pencycuron formulations can substitute the currently used hazardous organomercurials for the effcetive and safer control of black scurf of potato. It also improved the crop growth and yield to a slight extent. ACKNOWLEDGEMENTS Authors are thankful to Bayer (India) limited for supply of samples of monceren 250 SC and monceren 25 WP and for the financial assistance in the form of an adhoc research scheme on bioefficacy of new fungicides. REFERENCES Anonymous (2000). Annual Research Report. Department of Plant Pathology, Punjab Agricultural University, Ludhiana, pp.62. Dutt, B.L. (1979). Bacterial and fungal diseases of potato. Indian Council of Agricultural Research, New Delhi, pp.107. Kataria, H.R., Hugelshofer, U. and Gisi, U. (1991). Sensitivity of Rhizoctonia species to different fungicides. Plant Pathology 40:

6 44 Indian Phytopathology [Vol. 55(1) : 2002] Khanna, R.N. and Sharma Jyotsana. (1996). Effect of boric acid treatment on seed and soil borne Rhizoctonia solani inocula and rhizosphere microflora. J. Indian Potato Assoc. 23(1&2): 1-7. Khanna, R.N., Roy, S., Roy, R.P., Sharma, J., Jeswani, M.D. and Singh, P.H. (1991). Annual Scientific Report. Central Potato Research Institute, Shimla, pp.74. Khurana, S.M. Paul, Thind, T.S. and Mohan, C. (2001). Diseases of potato and their management. pp In: (Ed. T.S. Thind) Diseases of fruits and vegetables and their management. Kalyani Publishers, New Delhi. Somani, A.K. (1986). Non-hazardous chemical control of black scurf of potato. Indian J. agric. Sci. 56: Yamada, Y. (1986). Monceren (pencycuron) - A new fungicide. Japan Pesticide Information. 48: Received for publication April 23, 2001