ISHS Acta Horticulturae 431: Tospoviruses and Thrips of Floral and Vegetable Crops
DAMAGE-YIELD RELATONSHIP OF COMMON BEANS INFECTED BY THE BEAN FLOWER THRIPS |
| Author: | S. Kyamanywa |
| Abstract:
The bean flower thrips (Megalurothrips sjastedti) is one of the most serious pests of common bean (Phaseolus vulgaris) in Uganda (Nyiira 1973, 1978). Although information is lacking on the pest density at which economic loss occurs (i.e., economic injury level), prophylactic application of insecticides is recommended in Uganda. This study assessed bean-yield losses caused by M. sjostedti in both mono-and intercropping situations to determine the relationship between thrips population density and bean yield. The experiment was conducted at Makerere University Farm, Kabanyolo, which is 17 km north of Kampala. The first rainy season occurs from March to June and the second from October to December. Different thrips population densities on bean crops were achieved by applying Ambush CY (cypermethrin, a pyrethoroid) at three concentrations: no insecticide; Ambush applied at 100 mL/20 L of water (x); and Ambush applied at 2x. The insecticide was applied weekly using a 20-L knap-sack sprayer throughout the growing season. Dithane-M45 was also applied every 2 weeks at a rate of 3 g/L to control fungal diseases. Common bean cv. K20 was planted as a monocrop and intercropping with maize cv. Kawanda Composite. In both mono- and intercropping, beans were spaced at 60 cm between rows and 10 cm within rows. The maize was planted between the rows of bean at a spacing of 75 cm within rows. The experiment was planted in the second rainy season of 1989 and the first rainy seasons of 1990 and 1993. A split-plot design was used in which the insecticide treatments were in the main plot and the cropping systems were in the 6 x 6 m subplots. Each treatment was replicated six times. The thrips population was estimated using the alcohol washing method, starting 14 days after bean emergence (DAE). Fifteen leaf buds or flowers, depending on the growth stage of the bean, were picked randomly from each plot and preserved in glass vials containing 30% ethanol. The vials were later taken to a laboratory | |
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