Population dynamics and management of vectors of viruses causing maize lethal necrosis disease in Bomet County Kenya
Namikoye, Everlyne Samita
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Maize production in Kenya is under threat due to infection by maize lethal necrosis disease (MLND). The disease is known to cause intensive complete yield loss. It is caused by a synergistic infection of maize by maize chlorotic mottle virus and sugarcane mosaic virus which are mainly vectored by corn thrips (Frankliniella williamsi, Hood) and corn leaf aphids (Rhopalosiphum maidis, Fitch) respectively. This study was carried out with the aim of investigating the following aspects; farmer‘s knowledge and practices on vectors of MLND causing viruses, movement and dispersal of the two vectors in a maize farm and various management strategies through sticky roll trapping, varietal tolerance, action threshold levels, polycropping systems and biocontrol strategies towards the control of the disease and vectors. Field trials were carried out in Bomet County for two seasons from November 2014 to September 2016 using a randomized complete block design. Data was collected by counting vectors, scoring for MLND severity and disease incidence. Presence of MCMV, SCMV virus was also carried out using ELISA tests. Data was analyzed using Genstat version 17 to get mean and significant means were there after separated using LSD. Survey results indicated majority of respondents in Bomet as being youths aged between 21 to 30 years while 58% of the farmers had attained education up to upper primary level. Only 23% were high school graduates. Majority of the farmers were aware of MLND but only 3% knew about the vectors of MLND.The use of vertically positioned blue sticky traps were more attractive to corn thrips compared to the yellow ones (P = 0.023). Similarly, blue sticky rolls trapped more corn thrips and prevented maize from MCMV infection (P<0.001) while the yellow sticky rolls trapped more corn leaf aphids and prevented maize from SCMV infection (P<0.001). Sampling of maize along the rows gave the best prediction for the vector infestations (P<0.001) while the upper plant region proved most effective for vector sampling.The most appropriate time for vector sampling was from 8.30 am to 10. 30 am as well as from 3.30 pm to 5.30 pm. The monthly spray regime had the highest net returns as compared to all the other spray regimes. More over, maize from the entire thunder sprayed plots tested MLND negative compared to the control that received no spray (P<.001). Results showed variety Pannar as the most resistant to MLND (P<.001) as well as landraces MLR1 and MLR 15 (P = 0.002). The companion crops used in the polycropping system showed coriander harboring significantly more corn leaf aphids compared with other companions (P = 0.04). Furthermore, maize planted with coriander tested negative for SCMV and hence MLND negative. Findings from this study provide scouting and monitoring strategies for both vectors as well as various successful management and control methods for the disease and its vectors. Adoption of techniques such as sampling patterns, sampling time, scouting methods, use of sticky cards and sticky rolls will give an indication of the vector status in the field as well as offer control mitigation measures. Varietal resistance coupled with action thresholds of the vectors and the use of companion crops was able to result into minimal disease spread and reduced chances of MLND occurance. This information can be used to formulate a management strategy for the vectors of MLND causing viruses as well as develop a national vector and disease monitoring plan for both the vectors and the disease. This will culminate into improved maize production and food security.