Cassava Genotype Evaluation for Grasshopper Zonocerus variegatus (L.) (Orthoptera: Pyrgomorphidae) Susceptibility in Southern Sierra Leone

Reports of damage by grasshopper Zonocerus variegatus (L.) to cassava and other crops has increased in recent years. The attack on cassava is particularly threatening to the livelihood of many poor subsistence farmers in Sierra Leone. As such, an evaluation was conducted to investigate the use of host plant resistance as an alternative method of managing grasshopper rather than the sole reliance on chemicals. The experiment was laid out in a randomized complete block design with three replications. Two blocks were used (protected and unprotected) with twenty cassava varieties (Slicass 1 05-21, VT 05-02, Slicass 2, SN 05-22, Slicass 1 05-14, Slicass 2 05-17, Slicass 5, VT 05-07, SN 05-41, Slicass 1 05-05, 97/3202-05-04, Slicass 4, Slicass 1 05-42, SN 05-17, Slicass 1, Local, 97/0057-05-04, Slicass 6, 97/0057-05-01 and Slicass 2 05-13) in each block. Pest assessments was done at 3, 6, 9 and 12 Months After Planting (MAP) which coincides with the various seasons; rain, dry and dry-rainy transition periods. Significant differences were recorded in percentage incidence and severity score with respect to cassava variety and time of observation. While seven cassava varieties (Slicass 5, VT05-02, Slicass 4, 97/0057-05-04, 97/0057-05-01, slicass 6 and Slicass 1 05-21) were found to be less susceptible to Z. variegatus (L.), four varieties (Slicass 2 05-17, Slicass1 05-41, Slicass 2 05-13 and 97/005-05-04) out yielded (in terms of tuber weight and number) the released varieties during the two cropping seasons. Percent incidence and severity score was relatively high at 6MAP and 9MAP. Overall, tuber weight and number were higher in the protected plot compared to the unprotected plot during the two cropping seasons. Hence, protecting cassava field from grasshopper infestation may increase yield, number of tubers and invariably the production of good quality planting material that is resistance to grasshopper attack.