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Control of Foliage Diseases of Onion by Spray Fungicides

M. H. Ashrafuzzaman
Department of Plant Pathology, Bangladesh Agricultural University, Mymensingh.

M. U. Ahmad
Department of Plant Pathology, Bangladesh Agricultural University, Mymensingh.

Abstract/ Executive Summary:

The effectiveness of five fungicides (Benlate, Dithane M-45, Difolatan, Dithane z.78, and Cupravit) against Alternaria porri causing, purple blotch of onion was evaluated in the laboratory. The chemicals were tested at three concentrations (125, 250 and 500 ppm). Dithane M-45 and Benlate most effectively inhibited mycelial growth and spore germination. Others in order of their toxicity were Difolatian, Dithane Z-78 and Cupravit. In the field, efficacy of four selected chemicals was determined against purple blotch and leaf blast. Benlate and Dithane M-45 significantly increased yield by reducing the severity.

Keywords: Onion, Diseases, Fungicides

Location: Department of Plant Pathology, Bangladesh Agricultural University.

Start Date:

End Date:

Program Area: Pest Management

Commodity: Onion

Objectives:

To the control of leaf disease (leaf blast and purple blotch) of onion

Methodology:

Fungicidal efficacy on the mycelial growth and spore germination of Alternaria porri: In the laboratory, the merits of five fungicides (Benlate, Dithane M-45, Difolatan, Dithane z-78, and Cupravit) were evaluated on their relative ability to retared mycelial growth and spore germination. Single spore culture of Alternaria porri was made from infected onion leaves. Homogenous spores suspension was prepared in sterilized distilled water and one mi was poured over the surface of solidified PDA in the petri plates. the plates were rotated to assume even coverage of spores. Fungicidal preparations of three concentrations were made in sterile water. Filter paper discs of 5 mm diameter were cut, saturated with fungicidal preparation and a placed at the centre of each plate. The assay plates were incubated overnight at low temperature for allowing the fungicide to diffuse in the medium around the discs before germination of seeded spores. Later the plates were incubated at room temperature for 6 days. Each treatment was replicated thrice with a sterilized distilled water control. Comparative toxicity of the test fungicides was determined from the growth inhibition zone determined by measuring the diameter of clear zone. The method was followed for spore germination test. Fungicides were tested at three concentration (125, 250 and 500 ppm). The treatments were replicated thrice.Fungicidal efficacy against foliage diseases: Four out of five fungicides were evaluated in the field against leaf blast and purple blotch. A randomized block design with 3 replications was used. Each plot consisted of 10 rows of 25 plants of local variety of onion. Rows were spaced 6 inches apart and plants were spaced 5 inches apart in the row. Fungicidal preparations were applied for 10 days commencing from the time of initial appearance of the disease. In all 7 applications were made and fungicides were applied to the point of runoff , using a knapsack sprayer. Plants in the central 8 rows of each plot were examined for infection. Ten leaves were selected at random from different plants for examination. The extent to which the plants were affected was estimated according to the method described .

Source of Information: Bangladesh Horticulture,Vol- 4, No-2, Dec.1976

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

Fungicidal efficacy on the mycelial growth and spore germination of Alternaria porri: Dithane M-45 and Benlate were most effective inhibiting mycelial growth and spore germination followed by difolatan, Dithane Z-78 and Cupravit. In general, the fungicides at higher concentrations were more effective than at lower concentrations. At lower concentrations speculations was not much affected. However, at higher concentrations speculation was affected by Dithane M-45, Difolata and Benlate. In case of Dithane Z-78, morphological abnormality was observed in some spores. Similar effect on the spore of Piricularia oryzae has been reported.Fungicidal efficacy against foliage diseases: leaf diseases were considerably reduced by fungicidal sprays. Disease intensity was substantially reduced by Benlate and Dithane M-45 while Difolataa and Dithane Z-78 gave partial control. The yield data were analysed by the analyses of variance method. The performance of Benlate and Dithane M-45 were comparatively better than other chemicals in increasing yield. Although the foliage diseases were significantly controlled by Difolatan and Dithane Z-78, yield increase was not statistically different from the control. Benlate and Dithane M-45 significantly increased yield by reducing the severity of t he foliage diseases. As in many other cases (Wilcoxon et al, 1939), a fairly comparable relationship among the performances of different fungicides was obtained in the laboratory and field tests. In Bangladesh large acreages are cultivated with susceptible varieties of onion and chemical control should be adopted until resistant varieties are available to save the crop from serious foliage diseases.

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