Sampling procedures and Action threshold level of vectors of Maize Lethal Necrosis Disease causing viruses in Kenya.


Maize lethal necrosis disease (MLND) has emerged as a great threat to maize production in East Africa. The disease is caused by a coinfection of maize by maize chlorotic mottle virus (MCMV) and sugarcane mosaic virus (SCMV) that are vectored by corn thrips and corn leaf aphids. Due to the recent outbreak of MLND in Bomet County, Kenya, a study was carried out to determine the best scouting and sampling regime as well as action threshold levels for vectors of MLND causing viruses. The trial was laid down in randomized complete block design with four replications for each aspect in two seasons, from 1st April 2015 to 8th April 2016 in Bomet County, Kenya. Three maize regions; lower, middle and upper regions were sampled for vectors. Plants were also sampled between 8.30 to 10.30 am, 12.30-2.30 pm and 3.30-5.30 pm. Finally, five thunder (Imidacloprid and Beta cyfluthrin) spray regimes carried on a weekly, fortnightly, after three weeks and monthly basis was done. The upper plant region was a preferred target for corn thrips (P <0.001) while the lower part region was more preferred by corn leaf aphids (P=0.03). Scouting results showed the most reliable time for scouting to be either from 8.30-10.30 am or 3.30 to 5.30 pm (P=0.04). Maize from plots sprayed on a weekly basis had a significant decrease in corn thrips infestation compared to maize from plots not sprayed (P=0.01). Moreover, maize from thunder sprayed plots was MLND negative while the unsprayed maize was infected with MLND (P <0.001). Although yield of maize from weekly sprayed plots was higher than any other treatments (P <0.001), the net returns from monthly sprayed plots was higher. The action threshold level for corn thrips and corn leaf aphids was found to be 6 and 3 respectively. These findings provide information to farmers and other stake holders on how, when and where to scout and spray. If implemented properly, this will be able to minimize the wide spread of the virus by the vectors and eventually nib the chances of MLND occurring.

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