Evaluation of varietal resistance and pesticides as management strategies for thrips (megalurothrips sjostedti trybom and frankliniella occidentalis pergande) on french beans (phaseolus vulgaris l.)

Abstract

Evaluation of pesticides and varieties was undertaken in Kabete Campus Field Station during the period October 2001 to September 2002. Evaluation and screening of commercial French bean varieties and breeding lines was done during the period October 2001 to May 2002 to ascertain the susceptibility of these varietieslbreeding lines to thrips (Megalurothrips sjostedti and Frankliniella occidentalis). This was done using Randomized Complete Block Design (RCBD) and Completely Randomized Design (CRD). Five flowers were randomly picked and thrips counted under a dissecting microscope. Pod damage due to thrips was also rated on ten randomly harvested pods. It was evident from the study that there were significant differences among the varieties and breeding lines in thrips infestation. Commercial varieties had mean thrips numbers ranging from 38.3 to 89.4 and 15.7 to 28.2 in five flowers during first and second planting respectively. Monel variety was found to have the highest thrips infestation whereas Impala had the least. Among the breeding lines, line 950.1 had the highest mean thrips numbers of 1.84 thrips whereas lines 1169.1, 1182.2 and 825.2 had the lowest mean thrips numbers of 0.71 thrips per three flowers. Among a combination of breeding lines and commercial varieties, Monel registered the highest infestation level of thrips (70.2) whereas Piant recorded the least (27.9) per five flowers. Pod damage score also differed significantly among the varieties with Haricot 05 recording the highest score (2.84) whereas Piant recorded the least (1.37) per ten pods. Evaluation of pesticide/variety combinations for thrips infestation and damage was undertaken at Kabete Campus of University of Nairobi during the period June 2002 to September 2002. Four French bean varieties namely; Amy, Monel, Samantha and Impala selected from an earlier experiment were used. Four insecticides namely; . Lambdacyhalothrin (Karate 1.75 EC), Petroleum spray oil (DC Tron 500 ML), Spinosad (Tracer 480 SC) and Fipronil (Regent 50 SC) were used. This was done using split plot layout in a Randomised Complete Block Design with three replicates and repeated once. The varieties and the insecticides influenced thrips infestation independently. The insecticides Tracer 480 SC and Regent 50 SC gave the lowest thrips numbers across all the varieties. The mean number of F occidentalis in the Karate 1.75 EC sprayed plots was higher and significantly different from plots sprayed with Tracer 480 SC and Regent 50 Se. The mean number of M sjostedti was not significantly different for all the plots sprayed with Tracer 480 SC, Regent 50 SC and Karate 1.75 sc. The insecticide DC Tron 500 ML showed no significant difference (p=0.05) with the control plots.