Determination of economic injury levels and economic thresholds of Aphis craccivora and Maruca vitrata on cowpea

Experiments were carried out in Serere Agricultural and Animal Production Research Institute (SAARI) with the aim of establishing the economic injury levels and economic thresholds of aphids and pod borers on cowpea. The experiment to establish the relationship between aphid infestation and yields of cowpea and to determine the economic injury levels and economic thresholds of aphids on cowpea was conducted during the second rains of 1999 and first rains of 2000. It was observed that damage and yield losses of cowpea increased with increase in aphid density. The damage effects were generally severe when infestation was initiated at early vegetative and late vegetative stages of cowpea and to a lesser extent at flower bud initiation and pod initiation stages. During the second rains of 1999 for cowpea planted at the onset of rains economic injury levels of 2.7, 5.8, 14.8 and 17.5 aphids per plant was recorded at early vegetative, late vegetative, flower bud initiation and pod initiation stages, respectively while for cowpea planted four weeks after onset of rains economic injury levels of 4.4, 6.0, 46.4 and 10.6 aphids per plant were recorded for early vegetative, late vegetative, flower bud initiation and pod initiation stages, respectively. The corresponding economic thresholds were 2, 4.4, 11.1 and 13.1 and 3.3, 4.5, 34.8 and 8.0 aphids per plant for cow pea planted at the onset of rains and four weeks after onset rain, respectively. During the first rains of 2000, for cowpea planted at the onset of rains economic injury levels of 3.1, 7.2, 8.0 and 45.0 aphids per plant was recorded at early vegetative, late vegetative, flower bud initiation and pod initiation stages, respectively while for cowpea planted four weeks after onset of rains the corresponding economic injury levels were 3.1, 4.2, 8.4 and 14.2 aphids per plant. The corresponding economic thresholds were 2.4, 5.4, 6.0 and 33.8 and 2.4, 3.2, 6.3 and 10.7 aphids per plant for cowpea planted at the onset of rains and four weeks after onset rains.