The results of the field survey indicated that lower incidence of fall armyworm in the fields surrounded by tapioca and Nerium (Table 2). The incidence was 3.00, 5.50, 8.00 and 10.00% respectively on 15, 30, 45 and 60 days after emergence (DAE). The fields surrounded by tapioca alone also witnessed low incidence of fall armyworm
i.e 4.50, 8.00, 10.50 and 14.50% on 15, 30, 45 and 60 DAE respectively. It was followed by sorghum and cotton grown as an adjacent crop which recorded 15.00 and 25.00% incidence at 60 DAE, respectively. The higher incidence of 28.00% at 60 DAE was recorded where maize was grown as an adjacent crop.
Growing of border crops such as blackgram, sesame and cowpea recorded 24.50, 23.50 and 16.50% incidence at 60 DAE, respectively. Tapioca, nerium, cotton and sorghum were grown three months, one year and one month earlier than the maize sowing in the adjacent fields. The height of nerium and tapioca was 2 m and 1 m respectively at the time of maize sowing in the respective fields. The emerging maize plants were effectively protected from fall armyworm by these two adjacent fields. One critical observation was that one side of the field which doesn’t have any adjacent crop recorded more damage than the other sides of the field.
The results of the natural enemies population showed that growing of cowpea and blackgram as border crop recorded more natural enemies populations compared to all other combinations (Table 3).
The maize and black gram combination recorded 12.00, 13.00, 10.00 and 11.50% natural enemies and cowpea combination recorded 13.50, 15.00, 13.50 and 12.00% natural enemies during 15, 30, 45 and 60 DAE respectively. The maize and gingelly combination recorded 10.00, 9.50, 7.00 and 9.00 % natural enemies at 15, 30, 45 and 60 DAE, respectively. Though tapioca and nerium as adjacent crops recorded less fall armyworm incidence, the natural enemies’ population was less. The tapioca and nerium on either side of maize field recorded more number of natural enemies compared to fields where tapioca alone served as adjacent crop. The cotton and maize adjacent crops recorded lower numbers of natural enemies population compared to other crop combinations. The crop canopy of black gram and gingelly attracts more number of natural enemies compared to other crop combinations in the study.
Hailu et al., 2018 revealed that intercropping of maize with leguminous crops provided significant reduction of stem borers and fall armyworm compared to the mono cropped maize especially in the early growth phases and up to tasseling stage of maize.
Hailu et al., 2018 revealed that choice of companion crop, ratio of intercropping and time of sowing enhanced the fall armyworm control in maize. In the present investigation also the tapioca and Nerium are cultivated much earlier than maize sowing and thus favours the reduction in fall armyworm damage. Moreover, both are not preferred hosts for the FAW. In the climate adapted push pull strategy 82.7% reduction in average number of per plant and 86.7% in plant damage per plant were recorded compared to maize monocrop plots
(Midega et al., 2018). The white African black pepper extract and beans push cropping systems were suggested as an effective alternative management measure against the fall armyworm
(Tanyi et al., 2020). Whenever the choice of border or intercrop arises the researchers mostly focus on pulse crops whereas in the present survey tapioca and nerium are providing good control of fall armyworm as adjacent crops.
The results on the yield parameters indicated that maize grain yield was higher (76.8 q/ha) in maize crop adjacent to tapioca and nerium crop and it was followed by maize field adjacent to tapioca crop (76.2 q/ha) (Table 4).
The lower maize grain yield (72.7 q/ha) was recorded in the maize crop grown adjacent to maize crop. Though, considerable difference was not observed in grain yield, the net return (Rs. 86040/ha) and benefit cost ratio (2.65) was higher in maize crop adjacent to tapioca and nerium crop. The lower net return (Rs. 75360/ha) and benefit cost ratio (2.36) was realized in maize crop adjacent to maize crop. It might be due to the higher cost involved in managing the fall armyworm incidence in maize under maize crop adjacent to maize crop.
Daizy Sarma et al., (2018) also reported that intercropping of mustard and cowpea in cabbage reduced the diamondback moth population and increased the yield of cabbage.
The tapioca and nerium along with other crop combinations can be tried for the effective fall armyworm management. The major concern will be the planting of tapioca setts or nerium seedlings in and around the maize crop much earlier than the maize sowing. The days required for advanced planting and crop combinations should be studied in detail to devise effective fall armyworm management strategies in the new invaded areas.