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Maize Yield Losses from Stemborers in Kenya

  • Hugo De Groote (a1)

Maize is the major food crop in Kenya, where 2.3 million tonnes are produced annually to feed an estimated 28.6 million people (79 kg/person p.a.). Population growth in the country is high (2.9 % p.a.), resulting in increased pressure on arable land and, consequently, increased pest pressure on crops. Stemborers are one of the most important pests of maize. Previous research with artificial infestation established clear links between damage factors and yield losses. These results, however, cannot be extrapolated to estimate crop losses in farmers' fields under natural infestation. Due to lack of field data, farmers' (often subjective) estimates of losses under natural infestation and the incidence of infestation were used to estimate maize yield losses for each of Kenya's major agroecological zones. The yield loss was estimated to be 12.9 %, amounting to 0.39 million tonnes of maize, with an estimated value of US$ 76 million. High-potential areas have relatively low crop loss levels (10–12 %), while the low-potential areas have higher losses (15–21 %). Taking into account the higher yield of the former areas (more than 2.5 t/ha), the loss per hectare is remarkably constant, between 315 and 374 kg/ha, except for the dry mid-altitude zones, where losses total approximately 175 kg/ha. The value of these losses is estimated at US$ 61–75/ha and US$ 34/ha, respectively. Such estimates are useful for setting research and extension priorities.

Le maïs est la principale culture au Kenya, avec 2,3 million de tonnes produites annuellement pour nourrir une population estimée à 28,6 million (79 kg/personne et par an). La croissance dela population dans le pays est élevée (2,9 % par an), avec pour conséquence une pression croissante sur les terres arables, et une augmentation des problèmes dues aux ravageurs. Les foreurs sont un des ravageurs les plus importants du maïs. Des études antérieures, effectuées à partir d'infestations artificielles ont établi une relation étroite entre les pertes des récoltes et les dégâts lies aux foreurs. Toutefois, ces résultats ne peuvent pas être utilisés pour estimer les pertes dans les champs des paysans sous infestation naturelle. Pour palier à l'absence des données de terrains, les estimations des pertes sous infestation naturelle (souvent subjectives) et l'incidence de l'infestation telles que founis par les paysans, ont été utilisés pour estimer les pertes en recolte de maïs dans chaque zone agroecologique importante du Kenya. Les pertes moyennes ont été estimées à 12.9 %, équivalent à 0.39 million de tonnes de maïs d'une valeur approximative de 76 million de dollars. Les régions à haut potentiel ont généralement un taux de pertes plus faible (10–12 %) que les régions à faible potentiels (15–21 %). En valeur absolue, et du fait de rendements plus élevés dans les regions a haut potentiel, les pertes par ha sont relativement constante entre 315 et 374 kg/ha, excepté dans la zone sèche d'altitude moyenne où les pertes totales sont de 175 kg/ha. La valeur de ces pertes est estimée à respectivement 61–75 dollars par hectare et 34 $/ha. Ce genre d'estimations est utiles à la détermination des priorités de recherche et de la vulgarisation agricole.

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International Journal of Tropical Insect Science
  • ISSN: 1742-7584
  • EISSN: 1742-7592
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