Management of African root and tuber scale using improved cassava genotypes and mineral fertilisers.

The African root and tuber scale (ARTS), Stictococcus vayssierei Richard, is an insect species indigenous to Africa, which has recently become an economic pest of cassava ( Manihot esculenta Crantz) in many parts of the Democratic Republic of the Congo (D R C). This scale infests underground parts of the plants and prevents young plants from tuberising, thus, causing yield losses of up to 100%. In order to evaluate control components that can be combined into an effective strategy for the management of the scale, six improved cassava genotypes were evaluated for resistance against the scale and NPK fertiliser was tested at the recommended rate as a pest control component. The fertiliser application was made as basal dressing and on one improved clone (F100) with a local variety. Results indicated that ARTS infestations were delayed on ‘Kinuani', F100 and the local clone, ‘Kileba', as no scales were observed on them 6 months after planting (MAP). The sweetest improved genotype, ‘Papayi', harboured the highest number (134.8 insects plant-1) of scales. At 9 and 12 (harvest) MAP, all clones were relatively highly infested, except for the bitter genotype, ‘Sadisa'. This clone also yielded more than the local clone. Mineral fertiliser application significantly increased scale population density on F100, and plant height on both F100 and the local clone. It did not significantly affect the number of tuberous roots and root yield on either the improved F100 or on ‘Kileba'. Key Words: Democratic Republic of Congo, Manihot, Stictococcus vayssierei RESUME La gamme des racines et tubercules Africains, Stictococus vayssierei Richard, est une espece indigene a l'Afrique qui est recemment devenue une peste economique de manioc ( Manihot esculenta Crantz) dans beaucoup d'endroits de la Republique Democratique du Congo (RDC). Cette gamme infecte les parties souterraines des plantes et empeche les jeunes plantes a former les tubercules, causant ainsi des pertes de rendements jusqu\'a 100%. En vue d'evaluer les composants de controle qui peuvent etre combines dans une strategie effective pour la gestion de la gamme, six genotypes ameliores de manioc etaient evalues pour la resistance contre la gamme et le fertilisant NPK etait teste au taux recommande comme un composant de desinsectisation. L'application de fertilisant etait faite comme engrais fondamental et sur un clone ameliore (F100) avec une variete locale. Les resultats ont indique que les infestations de la gamme des racines et tubercules Africains etaient retardees sur ‘ Kinuani', F100 et le clone local, ‘kileba', etant donne qu'aucune gamme n'etait observee sur eux 6 mois apres plantations (MAP). Le genotype ameliore le plus sucre, ‘Papayi', a heberge le nombre le plus eleve (134,8 insectes plante-1) de gamme. A 9 et 12 mois (recolte) MAP, tous les clones etaient relativement gravement infectes, a l'exception du genotype amere, ‘Sadisa'. Ce clone a aussi produit plus que le clone local. L'application de fertilisant mineral a significativement augmente la densite de population de gamme sur F100 et sur le clone local. Il n'a pas significativement affecte le nombre des racines tubercules et la racine produite sur le F100 ameliore ou sur ‘Kilemba'. Mots cles : Republique Democratique du Congo, Manihot, Stictococus vayssierei African Crop Science Journal Vol.12(3) 2004: 217-222