Determination of damage threshold of cassava green mite (Acari: Tetranychidae) on different cassava varieties for pest management

Abstract

Density threshold has been least considered in efforts to control cassava green mite (CGM) of the Mononychellus species. Nine cassava varieties of varied cyanogenic contents were evaluated for CGM density threshold. Mite population of the 10 introduced individual active stages of Mononychellus progresivus reached peak densities on 39th day of t he m o s t susceptible varieties, and by the 54th day attacked leaves had wilted at 20.0 ± 2 °C and 63 ± 4% test climatic conditions. Mite threshold was determined to be ≥ 27 mites / leaf. C a s s a v a leaf variety cyanogens potential content was between 8.5 to 20.0 mg/kg on the nine v a r i e ti es evaluated. Variety high cyanogens potential led to higher CGM density growth and s ub s e q u en t biomass loss. Similarly, high leaf cyanide (HCN) content led to higher biomass loss (%) up t o HCN 20mg/Kg as a result of high CGM infestation. This information is beneficial to c a s s a v a breeders when developing varieties tolerant to CGM damage and safe for human c o ns um p ti o n where cyanogens levels <10mg/kg showed the least leaf damage by CGM. Likewise fa r m er s and crop protection agents can use the determined threshold to decide when to i m pl em e n t control measure for CGM on cassava cr o p.