Sweet potato weevils (Cylas puncticollis and C. formicarius) are notorious pests of sweet potato and cause severe losses in marketable yield. The study tested the use of Beauveria bassiana ((Balsamo) Vuillemin) (Deuteromycota: Hyphomycetes) for controlling sweet potato weevils. An experiment was conducted using four treatments: 1) dipping sweet potato cuttings in solution of 1 g/litre B. bassiana before planting, 2) spraying with the registered chemical Deltametrin at 50ml/100litre every 2 weeks for four months after planting, 3) spraying the leaves every 2 weeks with B. bassiana (10 g/100 litre) for four months after planting; and 4) a control (sprayed with distilled water). The experimental design was a Latin square with split plot design: pest management strategy as main plot factor and cultivars (Bophelo, Ndou and Blesbok) as subplot factors. Spraying with B. bassiana significantly reduced the percentage of insect damaged roots (5.31%) compared to the control (13.75%). Dipping did not significantly reduce the number of insect damaged roots (12.13%). There was no significant difference between the chemical spray (5.88% insect damage) and spraying with B. bassiana (5.31% insect damage). The preliminary investigation indicated that B. bassiana can be considered as an alternative control method for the sweet potato weevil.
Response of plant growth and essential oil yield of rose-scented geranium (Pelargonium capitatum × P. radens 'Rose') to withholding irrigation at different times of regrowth cycles was investigated at Hatfield Experimental Farm of the University of Pretoria, South Africa, from 2004 to 2007, and 1-month withholding irrigation periods during the 2nd, 3rd, or 4th month of regrowth were applied as treatments. Herbage yield showed a significant reduction when the water stress period was imposed during the 3rd or 4th month of regrowth. A remarkable essential oil yield loss was observed only when the plants were stressed during the 4th month of regrowth. Essential oil content (% oil on fresh herbage mass basis) apparently increased in the stressed treatments, but total oil yield dropped as a result of lower herbage mass. Essential oil composition changes in response to irrigation withholding treatments were not consistent. Water-use efficiency was not significantly affected by withholding irrigation in the 2nd or 3rd month of regrowth. With a marginal oil yield loss, c. 330-460 m 3 of water/ha per regrowth cycle could be saved by withholding irrigation during the 3rd month of the regrowth cycles. The overall results highlighted that, in water scarce regions, withholding irrigation during either the 2nd or 3rd month of regrowth could improve water productivity in rose-scented geranium.
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