On-farm development and testing of IPM packages for control of sorghum head-bugs in Mali

Improved caudatum sorghum cultivars have spread since their introduction in the late nineteen-eighties in the Kolokani area, Mali, being cultivated at the turn of the millennium by many farmers over hundred villages, under the name "Gadiabani". Being compact-panicled, these varieties are prone to damage by the panicle-feeding bug Eurystylus oldi. On-farm trials were conducted in 1998 and 1999 in respectively five and 16 villages of this area, to establish the status of castor bean (Ricinus communis) as a source of sorghum infestation by E. oldi, and evaluate the management of this alternate host plant, in combination with sowing date manipulation and use of host plant resistance, as potential control options for this pest. Experimental designs were split-plots with three factors. Both years, eight sorghum cultivars were planted in two dates (DOS). The third factor studied was vicinity with castor in 1998, and castor management in 1999. There were five replicates in 1998, and three in 1999. Head-bug numbers were recorded on maturing grains, and head-bug damage was visually rated at grain maturity. In 1998, infestation and damage by head-bugs on sorghum panicles in trials located close to castor plants were significantly higher than on those with no castor in their vicinity. In 1999, castor management either by insecticidal treatment or physical removal of flowering castor spikes on plants neighboring test plots, immediately before sorghum flowering, significantly reduced E. oldi populations on sorghum panicles. In both years, the effect of sowing date was not significant on head-bug population, while in 1998, head-bug damage scores were significantly higher on DOS1 than on DOS2. In 1998, the genotypic effect was significant for both parameters, the hybrid ICSH 89002 being the most infested and damaged genotype, while Malisor 84-7 and 94-EPRS-GII-1122 were respectively the less infested and the less damaged. In 1999, the genotypic effect was also significant, local guinea and head-bug resistant controls Bibalawili and Malisor 84-7 being the less infested cultivars, compared to ICSH 89002, ICSV 1063, Gadiabani and ICSV 1079, which suffered severe infestation, while 87W810 and 94-EPRS-GII-1122 had an intermediate ranking. These results definitely demonstrate the role played by castor as a significant source of sorghum infestation by head-bugs, and the prospect for reducing both infestation and damage, by management of this alternate host, in conjunction with use of host plant resistance and to a lesser extent planting date manipulation, in IPM programs.