Lure and infect strategy for application of entomopathogenic fungus for the control of bean flower thrips in cowpea

The efficacy of spot spray and cover spray applications of Metarhizium anisopliae (Metsch.) Sorok. in combination with the thrips attractant Lurem-TR (methyl-isonicotinate) was compared in field experiments for the management of bean flower thrips (BFT), Megalurothrips sjostedti (Trybom), on a cowpea crop in two seasons (June-December 2014). Treatments were applied five days after the placement of Lurem-TR in the field. During the first season, BFT densities per plant 5 days post-application were lower in spot spray (10.1 ± 4.3) and cover spray (11.5 ± 4.8) treatments than in the control treatment (41.8 ± 15.2). In the second season, 5 days post-application, the spot spray treatment recorded the lowest BFT density of 32.5 ± 6.0, followed by cover spray with 40.9 ± 7.0 thrips. The control treatment recorded the highest BFT density of 67.4 ± 10.3 5 days post-application. Conidial viability and thrips conidial acquisition did not differ between the two application methods. Grain yields of 1430.7 ± 114.2 kg and 1312.1 ± 87.7 kg were obtained in the cover and spot spray treatments, respectively, while 976.8 ± 105.2 kg in the control during the second season. The cost benefit analysis indicated profits with the spot spray than cover spray application due to the reduction in labor and the quantity of inoculum used. Spot spray application of biopesticides could therefore be a viable option for small-scale farmers for the management of BFT on cowpea.