Efficacy of some plant extracts in the management of cercospora leaf spot of groundnut in the Sudan savanna of Nigeria

Field trials were conducted to evaluate the efficacy of neem seed, garlic clove, onion bulb, ginger rhizome and pawpaw leaf extracts applied as foliar spray in controlling cercospora leaf spot of groundnut in the Sudan savanna of Nigeria during the 2002 and 2003 cropping seasons. Ridomil was used as a positive check while the control was left untreated. Three spray regimes (once, twice and thrice) were evaluated. A strip plot design with three replications was used in setting up the experiments. Ex-Dakar, a cercospora leaf spot susceptible Spanish Valencia groundnut variety, was used as planting material. All the plant extracts reduced the incidence and severity of cercospora leaf spot in both seasons compared to the untreated crops. However, neem seed and garlic clove extracts significantly reduced the incidence and severity of the disease compared to the other plant extracts. Ridomil was more effective in controlling the disease than the plant extracts. Three sprays with the plant extracts gave better control of the disease than one or two sprays in the season. The highest seed yield of 3115 kg/ha and 3311 kg/ha in 2002 and 2003, respectively, were obtained with neem seed extract treatment while the lowest seed yield of 2134 kg/ha and 2334 kg/ha in 2002 and 2003, respectively, were recorded from the untreated crops. Also the highest seed yield of 3124 kg/ha and 3418 kg/ha in 2002 and 2003, respectively were obtained following three sprays compared to 2523 kg/ha and 2641 kg/ha for one spray in 2002 and 2003, respectively and 2840 kg/ha and 3085 kg/ha for two sprays in 2002 and 2003, respectively. The highest haulm yield of 4121 kg/ha and 4089 kg/ha in 2002 and 2003, respectively were also obtained following treatment with neem seed extract. The lowest haulm yield of 2951 kg/ha and 3045 kg/ha in 2002 and 2003 respectively, were recorded from the control. Three sprays gave higher haulm yield (4265 kg/ha and 4279 kg/ha in 2002 and 2003, respectively) than one and two sprays in the season. Neem seed extract could therefore be used to control cercospora leaf spot and to improve groundnut production in the Sudan savanna of Nigeria.