S. Kyamanywa

Farmer-participatory evaluation of cowpea integrated pest management (IPM) technologies in Eastern Uganda

A three-season study was conducted with the goal of verifying integrated pest management (IPM) technologies developed at Makerere University for management of cowpea field pests. Ten IPM-field schools with 10–20 farmers were run for three consecutive seasons of 2000 A (first rains), 2000 B (second rains), and 2001 A. Each school evaluated seven treatments that included farmers’ practices; cowpea monoculture and cowpea/sorghum intercrop mixtures, and five varying insecticide spray regimes. The key insect pests targeted by the sprays included aphids, Aphis craccivora Koch, flower thrips, Megalurothrips sjostedi Trybom, the legume pod borer, Maruca vitrata Fabricius (formerly M. testularis Geyer), and a range of pod sucking bugs (i.e., Nezera viridula Linnaeus, Clavigralla tomentosicollis Stal., Riptortus dentipes Fab.). The experiment was a randomized complete block design with farms (i.e., field schools) as replicates. Results indicated that combining cultural practices and spraying once each at budding, flowering, and podding stages was more effective and profitable than spraying cowpea weekly throughout the growing season. An IPM practice which combined early planting, close spacing cowpea (30 � 20 cm 2 ), and three insecticide applications once each at budding, flowering and podding stages, had the highest yields of 791 kg/ha with a 51% yield gain over the farmers’ traditional practices. Farmer evaluation over the three seasons revealed that this practice was most preferred by farmers, with a farmer preference of 46.4%, 57.1%, 71.4%, and 89.3% at planting, vegetative, flowering and harvesting evaluation stages, respectively. r 2002 Elsevier Science Ltd. All rights reserved.

Determination of damage-yield loss relationships and economic injury levels of flower thrips on cowpea in eastern Uganda

Abstract Studies were carried out in eastern Uganda to assess the effect of legume flower thrips ( Megalurothrips sjostedti ) injury on cowpea grain yields and to establish economic injury levels (EILs) and action thresholds for thrips on cowpea. The studies relied on various insecticide spray regimes to obtain different thrips densities per experimental unit and use of exclusion cages in the field to confine defined numbers of thrips populations. A significant negative relationship ( y =−0.011 x +1.77; r =0.87; P =0.003) was observed in the field studies between thrips densities and cowpea grain yields. The EIL was established at seven thrips per inflorescence. The study also revealed that three well timed (i.e., applied after bud initiation to minimize flower bud abortion) insecticide sprays are effective in the control of thrips. The three sprays are regarded effective in that thrips densities were kept below the established thresholds. More than three sprays also reduced thrips populations to less than seven per inflorescence but these were not economical.

Pest management in cowpea. Part 3. Quantifying the effect of cowpea field pests on grain yields in eastern Uganda.

Abstract We used regression analysis to quantify yield variations in cowpea due to major insect pests, i.e., aphids (Aphis craccivora Koch), thrips (Megarulothrips sjostedti Trybom), Maruca pod borer (Maruca vitrata Fabricius) and a complex of pod-sucking bugs. Variability in pest infestation was created by growing Ebelat (an erect cowpea cultivar) in two locations over three seasons and under different insecticide spray schedules. Stepwise regression for individual locations and seasons’ data indicated that most of the variation in cowpea grain yields was caused by thrips. We estimated that to the total variation in cowpea grain yields, on average, the major pests contribute 51–69% in Pallisa and 24–48% in Kumi. Thrips alone contribute 35–41% and 13–19% at these two sites, respectively.