Efficacy and Mode of Application of Local Beauveria bassiana Isolates in the Control of the Tea Weevil

Abstract

The tea crop in Kenya ubiquitously is exposed to biotic and abiotic stresses which can be devastating. This includes damage by five species of 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) [Hust], among others, Adult weevils damage tea by defoliating nursery, 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; Kenya Tea Development Agency (KTDA) Igembe Factory catchment, Giciaro tea Farm of Meru District and Kenya Tea Development Agency (KTDA) Mununga Factory catchment. Mr. Njogu Kiruki’s farm. The fields were laid out in a random complete block design (RCBD) with three replicates. The treatments were of two efficacious locally isolated B. bassiana isolates applied at a rate of 1x1013 conidia/ha applied with two mode of application; a Solid state fermented mixture in wheat bran and a spores liquid formulation, Karate which was sprayed on trash and the control. The effect of weevils on productivity of tea was significant with reduction in yield of between 30-33%. Similarly, Data for damage scores, percentage damaged leaves and canopy cover varied significantly (P<0.05) with the control having the highest damage (57%compared to 52%) and reduced canopy cover. Mature leaves showed a higher percentage of damaged leaves compared to pluckable leaves The performance of B. bassiana isolates, applied in a solid substrate or sprayed as conidia on the foliage, was comparable to that of Karate at the rate of 2L/ha. This study suggests the possibilities of the use of B. bassiana isolates to control tea weevils using either mode of application.