Efficacy and mode of application of indigenous local Beauveria bassiana isolates in the control of the tea weevil compared to Karate

Abstract

The tea crop in Kenya ubiquitously is exposed to biotic and abiotic stresses which can be devastating. These include damage by five species tea weevils. Tea weevils reported to occur in Kenya include, the tea root weevil (Aperitmetus brunneus) (Hust), Nematocerus weevil (Nematocerus sulcalus), Systates weevil (Systates sp.), Kangaita/Kimari Weevil (Entypotrachelus meyeri) (micans/Kolbe) and Nyambene weevils (Sprigodes mixtus), among others. Adult weevils damage tea by defoliating nursery as well as newly established and mature tea orchard. Kimari/Kangaita weevils are documented to occur throughout the tea growing areas of Kenya. Occasional isolated epidemic outbreaks occur causing variable level of damage by defoliating mature tea bushes. Studies were conducted to determine the efficacy of two Beauveria bassiana isolate compared with a pesticide, Karate, which contains lambdacyholothrin as the active ingredient, in two different major tea weevils occurring geographic regions namely; i) Kenya Tea Development Agency (KTDA) Igembe Factory catchment, Giciaro Tea Farm of Meru District, and ii) KTDA Mununga Factory catchment in Kirinyaga County, Njogu Kiruki’s farm. In Njogu Kiruki’s farm, the fields were laid out in a random complete block design with three replicates. The treatments were of two efficacious locally isolated B. bassiana isolates at a rate of 1 x 10¹³ conidia/ha (in 200L of water ) applied with two mode of application; a solid state fermented mixture in wheat bran and broadcasted on trash and a spores liquid formulation sprayed on foliage. Karate was sprayed on trash and the control was the formulation used for spraying fungus that contained no B. bassiana propagules. The effects of the treatments on made tea yields, weevil damage, canopy formation and light interception were determined. The results show that there is a significant difference of the treatments on weevil damage on tea. The isolates in both mode of application performance were comparable to that of Karate which killed the weevils at the rate of .2L/ha in 200L of water. This study suggest the possibilities of the use of B. bassiana isolates to control tea weevils at the rate of 1 X 1013 conidia/ha.