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Effects of Intercropping ‘Orange-Fleshed’ Sweetpotato with Onion on the Level of Weevil Damage

The problem of household food and economic insecurity i.e. inability of families to produce and purchase enough food to meet basic needs is considered to be a major determinate of Malawi’s nutrition problems. The major nutritional disorder in Malawi is Vitamin A deficiency. Orange-fleshed sweetpotato (Ipomea batatas) was introduced through the program “Rooting out hunger in Malawi with nutritious orange-flesh sweetpotato” to combat Vitamin A deficiency in addition to providing the daily calorie requirement. Production of sweetpotato is however challenged by the sweetpotato weevil damages and rotting problems. Unavailability of acceptable improved varieties, high incidence of pests and diseases, and poor cultural practices are also the main causes of low yields. A field experiment was carried out in Dedza (Malawi) from April to November 2013 to assess the “effects of intercropping orange-fleshed sweetpotato with onion on the level of weevil damage” with the objectives of developing a biological efficient onion intercropping for orange-fleshed sweetpotato (OFSP) production and determining the agronomic productivity of the intercrop systems. The experiment was conducted in a Randomized Complete Block Design (RCBD) with four treatments; sole cropped OFSP and Onion, and OFSP+Onion intercropped at ratios 2:1 and 4:1 respectively.


Data were collected on the yield of OFSP roots and vines and onion bulbs, virus symptoms incidence and the level of weevil damages to the OFSP. Data were subjected to the general Analysis of Variance (ANOVA) using SAS statistical software version 9.1. and means were separated using Dunnett at alpha ≤ 0.05. Land use efficiency (Land Equivalent Ratio (LER)) was calculated to assess the relative advantage of intercrops compared to the sole culture. Gross margin analysis (GMA) was calculated to determine the economic benefits of the crops grown. Intercropped onion did not affect the growth and reproduction parameters of the orange-fleshed sweetpotato. Intercropping reduced the susceptibility of the weevils on sweetpotato and decreased the susceptibility of weevils on sweetpotato crops. Sole cropped OFSP were highly affected by the weevils. Intercropping practice at the OFSP-Onion ratio of 4:1 had the lowest weevil damage percentage followed by the Intercropping at 2:1 ratio.


There was no significant difference in virus symptoms incidence at 6-8 weeks after planting from all treatments, whilst at one month before harvest; intercropping practice at the ratio of 4:1 indicated the lowest percentage of virus symptoms. In terms of yield, the results indicated that intercropping practices produced higher sweetpotato roots than the sole cropped OFSP. There was no significant difference between treatments in terms of vines yield. The land efficiency was increased with the intercropping practices. The LER shows that intercrops at ratios 4:1 and 2:1 had ratios above 1 meaning that there was intercropping advantage over the sole crops. The economic analysis proved that intercropping would fetch better profits than the sole cropping. Intercropping at ratio 4:1 generated higher profits, followed by intercropping at 2:1. The profits attained from the intercropping were strongly generated from the sweetpotato productions. Sole cropped onion did was not able to generate profits.