Objective Pathogens causing the cowpea wilt disease and an effective control agent were identified.

Method Field surveys and statistical analyses were conducted to assess the prevalence of the wilt disease on cowpea plants at various growth stages. Infected plants were collected for pathogen isolation and purification in the laboratory. Suspected microorganisms were examined for morphological characteristics, analyzed for pathogenicity, and identified based on molecular determination. Mycelial growth rate as well as inhibitory effects on the potential pathogenic fungi and oomycetes under treatments of 10 fungicides were determined.

Result Preliminary, 135 strains of microbes and 128 of oomycetes were isolated and purified. They included fungi like Fusarium oxysporum and Nigrospora osmanthi and oomycetes like Phytophthora vignae and P. nicotianae that displayed the disease symptoms on cowpeas. The mycelial growth of F. oxysporum showed varying degrees of sensitivity toward the 10 fungicides. Prochloraz had the highest inhibitory effect of an EC₅₀ of 0.086 μg·mL⁻¹ followed by difenoconazole with an EC₅₀ of 0.241 μg·mL⁻¹ and carbendazim with an EC₅₀ of 0.944 μg·mL⁻¹, while copper oxychloride least effective with a dismal EC₅₀ of 14 719.994 μg·mL⁻¹. The inhibition rates of cymoxanil-azoxystrobin were 55.32% against F. oxysporum and 100% against P. vignae and P. nicotianae. It appeared to be the fungicide most effective for controlling, preventing, and treating the disease on cowpeas.

Conclusion The pathogens causing cowpea wilt was successfully isolated and identified for the first time to be F. oxysporum,P. vignae, and P. nicotianae, whose growth could be significantly inhibited by cymoxanil-azoxystrobin.