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Plant and animal health |
By Professor T.O.OSENI, MNIM Crop Production Programme, A.T.B.U.,Bauchi.Nigeria.
An experiment was conducted in a greenhouse at Abubakar Tafawa Balewa University, Bauchi, Nigeria during the cropping season of 2001 to evaluate the effect of garlic extract on cowpea scab disease. The treatments consisted of control, 25, 50, 75 and 100g/4litre garlic extract replicated four times. Cowpea yield and yield components was significantly (P=0.05) affected by garlic extract. Optimum disease control and grain yield was achieved with the application of 75g/4l garlic extract.
In Nigeria, crop protection measures is mainly dependent on chemicals which are not only scarce and expensive for resource poor farmers who are in majority but also hazardous to the environment and consumers. Cowpea, an important crop providing the cheapest source of dietary protein is attacked by a range of pests and diseases.
Cowpea scab caused by the fungus Sphaceloma sp. is one of the most destructive diseases of cowpea in the savannah zone of Nigeria (Emechebe, 1980). Fungicide application to seeds and foliar spray of plants have been found to check the disease, but not a common practice adopted by the farmers due to the high cost of the fungicide. Most plant pests and diseases are often unchecked resulting in decreased crop yield and low returns on capital investment. This paper presents the result of an alternative means of controlling cowpea scab disease using garlic extract.
The experiment was conducted in a greenhouse at A.T.B.U., Bauchi, Nigeria during the rainy season of 2001. The cowpea seeds of ‘Bogoro local’ were sown in 5 lit. Plastic pots containing 4kg Loamy sand soil. At 2 weeks after planting the seedlings were thinned to 2 plants/pot. After 3 weeks of planting, the cowpea seedlings were inoculated with Sphaceloma spp by placing on the axial of the upper canopy and at the base of the stand with infected dried cowpea plants. The seeds were sown on 29th July 2001. The treatments consisted of 4 concentrations of garlic extract and a control. The treatments were laid out in a randomised block design with 4 replications. The garlic extract were prepared by separately grating 25, 50, 75 and 100 g of fresh garlic bulbs with a blender. 200-ml. of hot distilled water was added to each extract and left for 24hrs. The solution was filtered and made up to 4lit. and a nut-sized piece of soap dissolved in the solution. The garlic extract application started 10 days after inoculation by spraying the plants with the solutions using micro sprayer at weekly intervals for 4 weeks while the control plants were sprayed with water. Assessments of the plants began 1 week after the first application until crop maturity. Severity was obtained using the visual assessment of Allens et.al; 1981 on leaf, stem, peduncle and pod. Numbers of pods/plant, seed/pod and grain yield were recorded. The data were analysed using ANOVA and LSD was used to separate the difference among the means.
The effect of varying concentration of garlic extract on cowpea scab disease is presented in Table. 1. There was significant difference between control (unsprayed) and the sprayed (treated) plants. The scab was more severe on control plants in that all the parts were severely affected. This indicated that garlic extract has a fungicidal property that is detrimental to Sphaceloma pathogens causing cowpea scab disease. The severity of the disease decreased with increase in garlic extract concentration. There was no significant difference in the severity of the disease beyond the application of 75g/4lit extract, which seemed to be the optimum for the control of the disease. Similarly, increase in the concentration of garlic extract significantly affected the yield and yield components with control giving lower yield than the treated plants. Also, 75g/4lit. gave grain yield of 187.3g/pot which was not significantly different from 100g/4 lit extract. The poor yield of the control was due to the high incidence of scab severity on the plants especially peduncles and pods. The pods were malformed and seeds poorly filled.
The present study showed that garlic extract at 75g/4lit is optimum for the control of cowpea scab. Garlic is presently used for human consumption but its potential as a fungicide can be exploited and developed. However, the garlic extract require further investigations to identify the active ingredients with a view to improving on this as a natural herbal fungicide.
Allens,D.j, Emechebe,A.M and Ndimande,B.(1981) Identification of resistance in cowpea to
disease of the savanna. Tropical Agriculture. 58:25-27.
Emechebe, A.M. (1980) Scab disease of cowpea caused by Sphaceloma species of fungus.
Ann.Appl. Biol. 96:11-16.
TABLE. 1. Effect of varying concentration of garlic extract sprayed
(at weekly intervals on Cowpea scab severity.)
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Concentration |