1. Introduction

Sorghum, Sorghum bicolar (L) Moench, is the major food crop grown by millions of people in Ethiopia. It grows in a wide range of environments although it is dominant in low land regions where drought and poor harvest are common occurrence (Birhane, 1977). Sorghum bicolor is an important crop in the North eastern part of Amhara National Regional State. Sorghum is grown particularly in areas with low rainfall. In most sorghum growing areas the farmers consume bread or ‘Injera’ made of sorghum flour alone or mixed with Teff.

The production of sorghum is threatened by a wide range of pre-and post harvest pests like stalk borer, sorghum chafer, sitophilus spp, etc. Till date more than 38 insect pests of stores are recorded attacking sorghum in Ethiopia (Adhanom and Abraham, 1986). Of these insect pests, Sitophilus spp.is the most common and perhaps the most destructive of all storage insect pests recorded in the northeastern region. Two species of Sitophilus sp. have been reported to attack sorghum. These include the maize weevil (Sitophilus zeamais Mostch) and the rice weevil (Sitophilus oryzae L.). It occurs in the tropical and subtropical belts as well as in warmer temperate region of all continents and is recorded very serious major pest of stored sorghum (Schumuttere 1990). Infestation often starts in the field and is carried later into the grain stores. About 15 percent weight loss had been reported in traditional storage facilities in Ethiopia (Yemane and Yilma, 1989).

Many farmers are interested in learning about non-chemical pest control, either because they have had insufficient money for pesticides, or because they are interested in farming more organically. So farmers in Ethiopia, use local herbs by mixing with grain to reduce infestation in stored grains (Yemane and Yilma, 1989). Based on the investigation made by Adane and Abraham (1995) and Mekuria (1995), there are promising botanicals which have insecticidal activity in the control of weevil. According to the practical field guide for the control of crop insects’ report of BOA (1997) and Stoll (1996,1998 and 2000), plants (Carissa schimperi leaves, Tagitus minuta leaves, Datura Stramonium leaves, Croton macrostachys leaves, Phytolace dodecandra leaves, etc…) have been identified for storage insect pest control. The objective of this study was, therefore, to evaluate the efficacy of some locally available botanicals to control Sitophilus zeamais Mostch and to determine the length of period the grain could protect by the different treatments.

2. Material and Methods

The trial was conducted under room temperature of 25-28⁰c and relative humidity at 70±5% in Kombolcha Plant Health Clinic Laboratory. The experimental sorghum seed (local) that were brought from a market that is more susceptible for such weevil were disinfected by phostoxin gas in the bulk before used for the experiment. The leaves of Tagitus minuta, Datura stramonium and Carissa schimperi were collected for the study in North Wollo. Collected leaves were washed with distilled water and shade dried at room temperature for twenty days and crushed into fine powder using domestic grinder (Table 1). Powders were kept in polythene bags at room temperature and properly sealed to prevent quality loss (Chayengia et al. 2010). Powders of each plant component were then mixed thoroughly with 500 gram grains in plastic jars roofed with muslin cloth and tightened with rubber band. Thirty adult weevils were released in each plastic jars. The combinations of the treatments were 3 botanicals plants (Tagitus minuta, Datura Stramonium and Carissa schimperi) with five concentrations (1%, 2%, 3%, 4%, 5%) w/w and standard check Malthion 5% dust at the rate of 10ppm (50 gram/100kg of seed). The sample without powder served as control. The 17 treatments were replicated three times. The design of the experiment was laid in Complete Random Design (CRD). A total of 51 plastic jars and 25.5 kg of Sorghum grains were needed for the experiment. Number of dead weevils was recorded every 21, 42 and 84 days after the treatments were applied. Hundred seeds were taken at random from each replication of a treatment for germination test. The seeds were placed in petri dishes containing moistened paper and number of germinated seeds was recorded after seven days. Percent weight loss was estimated using count and weight method taking 1000 seeds randomly from each replication from all treatments (Gwinner et al., 1996). The data was transformed to arcsine scale prior to analysis. Corrected observations were subjected to statistical analysis, Factorial ANOVA. The data was analyzed by using the general linear model procedure of the statistical analysis system (SAS Institute, 2003).

Where Wu = weight of undamaged grains

Nu = number of undamaged grains

Wd = weight of damaged grains

Nd = number of damaged grains

Table 1. Botanicals with their scientific, local and common names and their parts used in the study

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3. Results and Discussion

There were (p<0.05%) significant differences among treatments in the rate of mortality (Table 2). All botanicals significantly affected weevil mortality compared to untreated check, but not as effective as synthetic insecticides (Malathion 5% dust). Tagitus minuta (gimi) 1%, Datura stramonium (atsefaris) 1% and Carissa schimperi (merez) 1% were significance compared to untreated check, where as the remaining treatments where highly significance compared to untreated check. Tagitus minuta (gimi) 5% was highly significance to Tagitus minuta 1-3%, Datura stramonium 1-4% and Carissa schimperi 1-4%, while Carissa schimperi (merez) 5% were highly significance compared to Tagitus minuta (gimi) 1-4%, Datura stramonium (atsefaris) 1-5% and Carissa schimperi (merez) 1-4%. On the other hand the mean effects of Tagitus minuta 1-5% was significantly affect weevil mortality as compared to the remaining two botanicals mean effect. Maximum mortality caused by Carissa schimperi (merez) 5% followed by Tagitus minuta (gimi) 5%. In general, mortality rate was increased with increasing the concentration of plant extracts and exposure time. Among different plant powders, the grains treated with Tagitus minuta (gimi) 1%, Datura stramonium (atsefaris) 1% and Carissa schimperi (merez) 1% produced low mortality (Table 2).

All botanical treatments revealed significantly (p<0.05) higher mortality at 21 and 42 days of exposure when compared to the control. The killing effect of almost all botanicals at different concentration rates was high at 42 days after treatment than 21 and 84 days after treatment. All weevils with sorghum seed treated with malathion 5% dust died within 21 days of treatment; and couldn’t produce their progenies. In general the killing effect of all botanicals at different rat was highly reduced after 42 days after treatment (Table 3). That means the active ingredient persistence were lower after 42 days of treatments. Similar to Asmare (2002), the killing effect of botanicals is not acute as chemical insecticides in the first week after treatment. According to Adane and Abraham (1995) differences were observed among botanicals in speed of action within a month of storage period, i.e. some botanicals with different rate caused high mortality at 42 days after treatment.

Even though like weevil damage other factors, such as fungus and other storage insects also accounts for weight loss and germination percentage, the botanical treatment did not affect the germination percentage of sorgum. Good germination percentage was observed with malathion 5%, Datura stramonium (atsefaris) 5%, Carissa schimperi (merez) 5% and Tagitus minuta (gimi) 5%. Moreover there was significance difference among treatments in weight loss (Table 2).

Table 2. Effect of different treatments on germination and weight loss of sorghum seeds

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Table 3. Effect of treatments on adult weevil mortality (%) at days after treatment in laboratory

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4. Summary and Conclusion

The result shows that Tagitus minuta (gimi) 5% and Carissa schimperi (merez) 5% can solve poor resource farmers’ problems by integrating them with other cultural measures. The present study has shown the effectiveness of some botanicals at different rate in controlling maize weevil on stored sorghum in Ethiopia. However further research are needed to fix the rate graph and the long term effect in large stores of farmers conditions.

Acknowledgement

He expresses deepest appreciation and special thanks to Kombolcha Plant Health Clinic Laboratory for providing technical and material supports of this research work.

References

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