Chemical control of Septoria leaf spot on cowpea [Vigna unguiculata (L.) Walp.] in Kenya.

Three foliar fungicides namely, Antracol, Kocide 101 and Folicur were evaluated for the control of Septoria leaf spot caused by S. vignicola V.G. Rao on cowpea [Vigna unguiculata (L.) Walp.] at two field sites in Kenya: Kabete and Katumani. The cowpea variety used was the high yielding Machakos 66 that was also susceptible to Septoria leaf spot. Reduction in disease incidence and severity of Septoria leaf spot on cowpea was obtained with the three fungicides. However, significant (P ≤ 0.05) increase in seed yields was obtained when Kocide 101 and Antracol were applied to cowpea plants with the disease at Katumani. Folicur was found to be phytotoxic to cowpea plants and hence reduced plant dry weight and seed yield at both sites. Based on the cost-benefit analysis of the fungicides in the present study, Antracol and Kocide 101 are recommended for the control of Septoria leaf spot on high yielding cowpea varieties in arid and semi-arid areas. The Pearson correlation (r) between the disease incidence and seed yield was 0.75 (P = 0.46), while that between disease severity and seed yield was 1.00 (P = 0.01).