Management of cassava green mite Mononychellus progresivus (Acari: Tetranychidae) in different agro-ecological zones of Kenya

Abstract

The cassava green mite (CGM), Mononychellus progresivus Doreste, causes serious leaf damage on cassava leading to low root yield in the dry savanna regions of Africa. A study to compare effectiveness of the predatory phytoseiid Typhlodromalus aripo (De Leon), an acaricide abamectin, an insecticide chlorpyrifos and fertilizer in management of CGM was carried out in various agro-ecological zones of the eastern dry low-midlands at Katumani (LM4), Kiboko (LM5), the cool upper midlands at Embu (UM2) and the warm humid coastal lowlands at Mtwapa (CL3) of Kenya. The acaricide abamectin was found most efficacious in controlling CGM at all agro-ecological zones. Further, the results revealed that the exotic phytoseiid T. aripo was effective in suppressing population densities of CGM by 45% in the dry-hot midlands (Kiboko) and 64% in the warm-humid coastal climatic zone, but the predator could not persist in the cool midlands. However, in the same cool midlands, high amounts of rainfall led to low CGM density of less than 20 mites per leaf, amid the presence of the indigenous phytoseiid Euseius fustis (Pritchard & Baker). Increase in CGM density was positively correlated to the warm and hot dry environment at the plots at Kiboko and Katumani. In the irrigated and wetter sites T. aripo increased with the increase in relative humidity in the environment at Kiboko and Mtwapa. Abamectin spray was the best option in suppressing CGM densities in the dry lowland zones. Similarly, soil fertility input led to higher yield in the sandy soils of low coastal and eastern midlands. High CGM densities did not result in low yield as other environmental factors such as soil fertility, and temperature influenced the final root yield. These findings give insight on the management options of the CGM pest in the different agro-ecological zones in Kenya and similar regions of Africa