Susceptibility of to nematodes in Kagera Region, Tanzania

PR SPEIJER Susceptibility of Musa Sensibilité aux Sensibilidad a los International lnstitute cultivars to nematodes nématodes de cultivars nematodos de cultivares of Tropical Agriculture in Kagera Region, de bananiers exploités de bananos explotados East and Southern Africa Regional Center Tanzania. dans la région de Kagera, en la regi6n de Kagera PO Box 7878 en Tanzanie. en Tanzania. Kampala Uganda ABSTRACT RÉSUMÉ RESUMEN (Musa spp) are one of the La banane (Musaspp) constitue El banano, (Musaspp) constituye CH BOSCH dominant food crops in the l'une des principales productions una de las principales producciones Tanzania/Netherlands highlands of East Afr ica. A survey alimentaires des hautes terres de alimentarias de las alturas del Este Farming Systems Research was conducted in the Kagera l'Est africain. Une enquête a été afr icano. En la regiôn de Kagera en Project Region in order to determine conduite dans la région de Kagera Tanzania se efectuô una encuesta Lake Zone production constraints in the en Tanzanie pour déterminer les para determinar los apremios de ARI Maruku cropping system. East contraintes de production liées au producciôn ligados con el sistema P0 Box 1216 African Highland cooking bananas système de culture des bananiers. de cul tivo de los bananos. Ciertos Bukoba (Musa AAA, Marooke group) and Certains cultivars de bananes à cuire culcivares de plâtano blanco (Musa Tanzania ro a larger extent beer bananas (MusaAAA, groupe Matooke) et à AAA, grupo Marooke) y para (Musa AAA, Mbire group) were bière de ces régions (Musa AAA, cerbeza de estas regiones (Musa observed to be replaced by the groupe Mbire) auraient été AAA grupo Mbire) , se hubieran cultivars Gros Michel (Musa remplacées par les cultivars Gros sustituido por los cultivares Gros AAA) , Pisang Awak (Musa ABB) Michel (Musa AAA) , Pisang Awak Michel (Musa AAA) , Pisang Awak and Kanana (Musa AB). The (Musa ABB) et Kanana (Musa AB). (Musa ABB) y Kanana (Musa AB). common nematode species in Lesespèces de nématodes observées Las especies de nemâtodos banana roots were Pratylenchus dans les racinesde bananiers ont été observadas en las raizes de bananos goodeyi (with high densities Pratylenchusgoodeyi (en fortes densités fueronPr atylenchusgoodeyi (en considering the other species) , par rapport aux deux autres) , fuertasdensidades comparadas con Helicotylenchusmul ticinctusand Helicotylenchus multicinctuset las ocras dos) , Helicotylenchus Meloidogyne spp. Densities of Mehidagynespp. P goodeyi a été multicinctus y Meloidogyne spp. P goodeyiwere consistently higher beaucoup plus fréquent chez les P goodeyi fué mucho mâs frecuente in the East African Highland cultivars traditionnels de bananes à en los cultivares tradicionales de cooking and brewing cultivars chan cuire et à bière des régions étudiées plâtanos blancos y para cerveza de in the cultivars Gros Michel, que chez Gros Michel, Pisang las regiones estudiadas que en Gros Pisang Awak and Kanana. The Awak and Kanana. La sensibilité à Michel, Pisang Awak y Kanana. La East African Highland banana P goodeyi, plus fortepour ces sensibilidad a P goodeyi,mâs fuerte cultivars were expected to be more anciens cultivars que pour ceux para estos antiguos culrivares que Received 8 April 1994 susceptible to P goodeyichan more introduits récemment, pourrait para los mâs recientes podrfa Accepted 12 June 1996 recently introduced cultivars. expliquer leur remplacement par explicar su susriruciôn por estos ces nouveaux cultivars. nuevos cultivares.

Fruits, 1996, vol 51 , p 217-222 © Elsevier, Paris KEYWORDS MOTS CLÉS PALABRAS CLAVES T anzania, Musa, varieties, pest Tanzanie,Musa, variété, résistance Tanzania, Musa, variedades, resistance, plant nematodes, aux organismes nuisibles, néma­ resistenciaa las plagas, nematodos surveys, Pratylenchusgoodeyi, tode des plantes, enquête, de las plantas, enruescas,Pratylmchus Helicotylenchus multicinctus, Pratylenchusgoodeyi, He!icotylmchus goodeyi, Helicotylenchus Meloidogyne. multicinctus,Meb idof,Yne. multicinctus, Mebidogyne.

Fruits, vol 51 (4) 217 SPEIJER, BOSCH

and AB cultivars are used for cooking, and the introduction Gros Michel only rarely. The fruitsof the The Lake Victoria Basin counrries, viz Uganda, cultivars Gros Michel and Kanana are occasion­ Tanzania and Kenya, produce and consume 18% ally consumed as dessert fruits. of the world banana production (FAO, 1991). In Surveys ro evaluare pest pressure to Musa were Tanzania, major banana production is at higher carried out in the Kagera Region. They revealed elevation regions with abundanr rainfall, such as chat the dominant nemarode species were Pra­ the Kagera Region (EVERS, 1992). tylenchusgood eyi (Sher and Allen) and Helicotylen­ In the Kagera Region, the East AfricanHighland chus multicinctus (Cobb, Golden); Radopholus banana (Musa AAA) forms the dominant group similis(Cobb, Thorne) was observed occasionally of cultivars (BOSCH et al, 1994). Ir includes (WALIŒR et al,1984 ; BRIDGE, 1988; SIKORAet al, cooking or Marooke cultivars and brewing or 1989). A more detailed survey was conducted ro Mbire cultivars (BOSCH et al, 1995). In addition derermine constrainrs ro Musa production look­ ro the East African Highland beer banana, the ing into soi! ferriliry, cultivars, pests, diseases and cultivars Gros Michel (Musa AAA), Pisang Awak management pracrices (BOSCH et al, 1994). This (Musa ABB) and Kanana (Musa AB) are grown paper presenrs data on Musa cultivars and nema­ for brewing purposes (table I). None of the ABB rode species.

Table 1 Banana cultivars and their distribution in the survey in Kagera Region, Tanzania.

Cultivar Genome group Synonym1 Common use Common name

2 Nshakara AAA (Matooke-EA ) Enshakara; Musakala Cooking

Nshansha AAA (Matooke-EA) Kisansa Cooking

Nyoya AAA (Matooke-EA) Njoya Cooking

Mbire AAA (Mbire-EA) Mbidde Beer

Kijoge AAA Gros Michel; Bogoya Beer / dessert

Kisubi ABB Pisang awak; Kayinja Beer / dessert

Kanana AB ?Ney poovan; Sukali Ndizi Beer

3 4 Cultivar Village Location Bulamula Muzinga Kyaitoke Musira Buhekera Ntoija Nshakara + + + + + Close

Nshansha + + + + + + Close

Nyoya + + + + + Close

Mbire + + + + Distant

Gros Michel + + + + Distant

Pisang Awak + + + + + + Distant

Kanana + + + + + + Distant

1 (KARAMURA and KARAMURA, 1994); 2 EA: East African Highland banana; 3 +: cultivar present in sample; 4 close: cultivar is generally grown close ta the homestead; distant: cultivar is generally grown at a distance from the homestead.

218 Fruits, vol 51 (4) MUSA CULTIVARS AND NÉMATODES

2 ml aliquots froma 25 ml suspension, and den­ materials and methods sities per 100 g freshroot weight were estimated.

In the Kagera Region, six villages and 20 farm The villages and cultivars wirhin villages were households wirhin each of rhese villages were selected randomly. The observed nematode counts forthe three dominant species, P goodeyi, selected. A farm household contained several H multicinctus and Meloidogyne spp, were trans­ fields. From each household, one field was se­ formed using the square root (counts + 0.5) lected, which included an area close ro the house. transformation (GOMEZ and GOMEZ, 1984) . Such a field is called a Kibanja (BOSCH et al, Pair-wise comparisons of least squares means 1994) . Generally wirhin 15 m or more of the (LSMEANS) of transformed counts were per­ house, the soi! is more fertile, due to household formed using the general linear models (GLM) refuse, chan furrher into the field (BOSCH et al, procedure and LSMEANS statement in SAS 1994) . ln addition, the cooking cultivars are (anon, 1987) . Furthermore, genome groups were grown in relatively higher numbers chan the beer formed and differences evaluated. Components cultivars nearer to the house (BOSCH et al, 1995) . of variance were also esrimared in SAS (VAR­ ln each Kibanja, two cultivars were selected, one COMP procedure). grown close to the homesread and anorher furrher into the field. For each cultivar, three mats were sampled. A group of banana plants growing from results and discussion connected rhizomes is definedas a mat. No single cultivar was grown in ail the villages. Therefore, Ir was observed chat East African Highland cook­ the survey team selecred commonly grown culti­ ing cultivars and, to a larger extent, the East vars, three cooking and four beer (table I) . The African Highland brewing cultivars had been three East African Highland cooking cultivars replaced with exotic beer cultivars (anon, 1989; selected were consistently identified by farmers BOSCH et al, 1995) . The cultivar Gros Michel is and researchers (ROSSEL and MBWANA, 1991; the most common replacement, followedby Ka­ BOSCH et al, 1995) . The East African Highland nana and PisangAw ak (MUKANDALAer al, 1994) . beer cultivars were more difficultto differentiate Currently 65% of ail mats in the survey were in the field and were, rherefore, grouped as one classified as East African Highland cooking cul­ tivars, 9% as East African Highland brewing Mbire cultivar. The other beer cultivars selected cultivars and 26% as exotic brewing cultivar were Gros Michel, Pisang Awakand Kanana and (BOSCH et al, 1995) . ln the lare 1960s, 98% of are well described (ROSSEL and MBWANA, 1991). the mats grown in the Kagera Region were East They are generally referred to as 'exotic' culri vars African Highland cultivars; 70% of these cultivars as rhey are considered to be more recently intro­ were cooking and 30% brewing cultivars (FRJE­ duced into the region (KARA.MURA and KA­ DRJCH, 1968; RA.Lo and RALD, 1975), which RAMURA,1994) . suggests a 24% overall reduction in East African Root samples were collected from plants at the Highland cultivars. The East African Highland early flowering stage (floweremerges - fruitshori­ brewing cultivars appear to have been replaced by zontal) in an excavation of 25 cm X 25 cm exotic beer cultivars in excess of 70% during the x 25 cm, at 25 cm fromthe base of the flowering last 25 years. The replacement may possibly be plant. Roots fromeach of the rhree mats selecred linked to nematode susceptibility; therefore, the per cultivar were observed for root necrosis and nematode densities were compared forthe differ­ then combined (BOSCH et al, 1994) . Samples ent cultivar groups. were stored at approximately 8 °C forup to one P goodeyi was the dominant nematode species at month prior to nematode extraction. Nematodes ail sites and for all cultivars (table II). H multi­ were extracted from a macerated 5 g subsample, cinctus and Meloidogyne spp were also commonly using a modified Bearman funnel technique observed; however, in consistently lower den­ (HOOPER, 1990) . Extraction rime was 16 to sities. R similis and P cojfeae were occasionally 20 hours at room temperature, approximately observed, but always in very low densities of less 24 °C. Nematodes were counted rhree rimes in chan 300 nemarodes per 100 g freshroot weight

Fruits, vol 51 (4) 219 SPEIJER, BOSCH

Table Il Nematode densities per 100 g fresh root weight of seven Musa cultivars grown in six villages in Kagera Region, Tanzania.

Cultivar Genome group n Pgoodeyi H multicinctus MeloidogYf)espp

Nshakara AAA (EA1 ) 21 23,300 70 250

Nshansha AAA (EA) 54 14,260 610 20

Nyoya AAA (EA) 39 9,370 1,890 160

Mbire AAA (EA) 33 11,090 380 170

Gros Michel AAA 27 1,950 680 BQ Pisang Awak ABB 24 1,670 590 90

Kanana AB 30 1,270 130 330

Village Altitude masl n Pgoodeyi H multicinctus Meloidogynespp

Muzinga 1 ,500-1 ,600 39 14,490 130 290

Bulamula 1 ,460-1 ,500 37 16,990 50 250

Ntoija 1 , 160-1 ,300 34 3,840 1,170 100.

Musira 1 , 1 60-1 ,235 40 9,650 240 130

Kyaitoke 1,280 37 7,470 740

Buhekera 1 ,220-1 ,280 41 3,540 1,790 90 1 n: number of samples; EA: East African Highland banana; Pratylenchusgoodeyi and Helicotylenchusmulticinctus: jüveniles + females + males; Meloidogynespp : juveniles.

(table III). The nematode species profileobserved genome groups AM (East African Highland in the Kagera Region is similar to those observed types), AB and ABB were different between the in Uganda (KASHAIJA et al, 1994; SPE]JER et al, genome groups (P = 0.0001), but not amortg the l 994a,b), Kenya (SPE]JERet al, 1993) and Came­ villages (P = 0.1326). Genome differences ex­ roon (SARAH, 1989; BRJDGE et al, 1995) at simi­ plained 19.5%, while village differente ac­ lar elevations. counted for 0% of the variation. The P goodeyi Of the mats sampled, 64.5% were classified as densities observed for the AM genome group East African Highland banana cultivars, 13.2% were significandy higher (P -:;, 0.0014), than for as PisangAwak, l l.8% asGrosMicheland 10.5% the AB and ABB group (table IV). The relatively as Kanana. TheP goodeyi densities on EastAfrican higher densities of P goodeyi suggest chat the East Highland cultivars differedfor the villages Bula­ African Highland banana cultivars are more sus­ mula and Buhekera (P = 0.0421); however, they ceptible to P goodeyi chan the exotic MusaAB and did not differ among the Highland cultivars ABB cultivars. The higher susceptibility of the within the villages (P = 0.2813). Much of the East African Highland cultivars to P goodeyi may variation (92.8%) in nematode counts for the be the reason fortheir gradual replacement by the Highland cultivars remains unexplained; how­ Jess susceptible exotic cultivars. The relatively ever, this may be attributed to differences in high replacement of Mbire cultivars may be ex­ nematode densities in planting material used, plained by the facechat they were generally grown management or plantation age. The cultivar Gros further away from the homestead chan the Ma­ Michel was mainly grown at one location, Buhe­ tooke cultivars. Therefore, Mbire cultivars re­ kera, and was cherefore excluded from further ceived less additional nutrients from household analysis. The P goodeyi densities on the Musa waste and their root system may develop at a

220 Fruits, vol 51 ( 4) MUSA CULTIVARS AND NÉMATODES

Tablê Ill Occurrence of Radopholus similis (Rs) and Pratylenchus coffeae (Pc) in Musa cultivars in Kagera Region, Tanzania. Cultivar Village Bulamula Muzinga Kyaitoke Musira Buhekera Ntoija Nshakara Rs

Nshansha Rs Pc Rs Pc Pc

Nyoya Pc

Mbire Pc Pc Pc

Gros Michel

Pisang Awak Rs

Kanana

Table IV Comparison of Pratylenchus goodeyi densities for the Musa genome groups AAA (East African Highland type), ABB and AB, using least square means for the transformed nematode densities. Genome P goodeyi density P values for comparison of transformed 1 nematode densities 2 AAA (EA ) ABB AB AAA (EA) 13,542 0.0014 0.0002

ABB 1,670 0.8164

AB 1,270

1 2 2 : Nematode density transformation using square root (counts + 0.5); : EA East African Highland banana. slower pace, further reducing its tolerance to nematode attack. • ref erences ln Kenya, SPEIJER and SIKORA (1990) observed Anonymous (1 987) SAS-Statistica/ package. Cary, results comparable to those observed in the Ka­ NC 2751 2-8000, USA, SAS lnstitute Inc gera Region, such as high densities of P goodeyi in Anonymous (1 989) Diagnostic survey of Bukoba Nakyetenguof the East AfricanHighland banana District. Amsterdam, the Netherlands, Agri­ group as compared to low densities in Kanana cultural Research lnstitute (ARI) and Maruku Bukoba and Royal Tropical lnstitute (KIT) , grown on farms. Only limited data are available working paper no 3, Tanzania/Netherlands forcomparison of cultivar performancein other Farming Systems Research Project, Lake Zone regions. ln Cameroon, PRICE (1994) observed Bosch CH, Ndile RM, Sentozi E, Mgenzi SR (1 994) low P goodeyi densities forBanane Cochon of the Diagnostic survey constraints ta banana East African Highland bananas group and high production in Bukoba and Muleba Districts: 1-Methodology. Amsterdam, the Netherlands, densities for Christine and Pelipita of the Musa Agricultural Research lnstitute (ARI) and Maruku ABB group. Comparison ofhost plant response Bukoba and Royal Tropical lnstitute (KIT) , field is difficultbecause the same cultivars were not note no 47, Tanzania/Netherlands Farming Systems Research Project, Lake Zone, 23 p available in each region. However, the results Bosch CH, Lorkeers A, Ndile MR, Sentozi E (1 995) suggest that a considerable variation in nema­ Diagnostic survey: constraints to banana in Bukoba tode host response to P goodeyi may exist for and Muleba Districts, Ka gera Region, Ta nzania. cultivars from the same genome group. ln ad­ Amsterdam, the Netherlands, Agricultural Research dition, different pathotypes forP goodeyi may lnsiitute (ARI) and Maruku Bukoba and Royal Tropical lnstitute (KIT), Working paper no 8, be expecced, as have been observed forR similis Tanzania/Netherlands Farming Systems Research (SARAH et al, 1993). Project, Lake Zone, 102 p

Fruits, vol 51 (4) 221 SPEIJER, BOSCH

Bridge J (1988) Plant nematode pests of ban ana. in Rossel G, Mbwana ASS (1991) Identification of East Africa with particular reference to Tanzania. banana cultivars in the collection of the Maruku ln: Nematodes and the weevil borer in bananas. Agricultural Research lnstitute. Amsterdam, the Present status of research and outlook. Netherlands, Tanzania/Netherlands Farm1ng Proceedings of a workshop held in Bujumbura, Systems Research Project and Royal Tropical Burundi, 7-11 December 1987, 99 p. lnstitute (KIT), 29 p Montpellier, France, International Network for Sarah JL (1989) Banana nematodes and their contrai the lmprovement of Bananas and Plantain in Africa. Nematropica 19 (2), 199-216 (INIBAP), 35-39 Sarah JL, Sabatini C, Boisseau M (1993) Differences Bridge J, Price NS, Kofi P (1995) Plant parasi c U in pathogenicity to banana (Musa sp, cv Poyo) nematodes of plantain and other crops 1n among isolates of Radopholus s1m1/is from Cameroon, West Africa Fund. Appt Nematol 18 different production areas of the world. Nema­ (3) , 251-260 tropica 23 (1), 75-79 Evers G (1992) Banana cultivar diversity in the area of Morogoro, Tanzania. Fruits 47 (3) , 377-391 Sikora RA, Bafukazara ND, Mbwana ASS, Oloo GW, Uruno B, Seshu Reddy KV (1989) lnter­ FAO (1991) FAO yearbook production. Rome, ltaly, relationships between banana weevil, root lesion FAO Statistics Series no 99 nematode and agronomie practices and their Friedrich KH (1968) Coffee-banana holdings at importance for banana decline in Tanzania. FAO Bukoba: reasons for stagnation at a higher level. Plant Protection Bulletin 37 (4) , 151-157 ln: Smallholder farming and smallholder Speijer PR, Sikora RA (1990) lnterrelationships development in Tanzania, ten case studies. between Pratylenchusgoodey, and root rott1ng Munich, Germany, Ruthenberg H (ed) , IFO fungi affecting banana in Kenya. ln: Proceedings Africa-Studies, no 24, 175-212 Second International Nematology Congress, Gomez KA, Gomez AA ( 1984) Statistical procedures held at Veldhoven, Netherlands, 11-17 August for agricultural research. , Inter­ 1990, p 140 national Rice Research lnstitute, New York, NY, USA, J Wiley & Sons, 680 p Speijer PR, Budenberg JW, Sikora RA (1993) Relationships between nematodes, weev1ls, Hooper DJ ( 1990) Extraction and processing of plant banana and plantain cultivars and damage. and soil nematodes. ln: Plant paras1tlc Annua/s of Applied Biology 123 (3) , 517-525 nematodes in subtropical and tropical agri­ culture. Wallingsford, Oxon, UK, CAB Inter­ Speijer PR, Gold CS, Karamura EB, Kashaija 1.N national, Luc L, Sikora RA, Bridge J (eds) , 45-68 (1994a) Assessment of nematode damage 1n East African Highland banana systems. ln: Karamura DA, Karamura EB (1994) A provisional Proceedings of a conferencelworkshop on checklist of banana cultivars in Uganda. nematodes and weevil borer affecting banana in Montpellier, France, National Agricultural Asia and the Pacifie, Kuala Lumpur, Malaysia, Research Organisation (NARO), International 18-22 April, Los Banos, Laguna, Philippines, Network for the lmprovement of Banana and 258 p. INIBAP, Valmayor RV, Roa VN (eds) , Plantain (INIBAP) , 28 p 191-203 Kashaija IN, Speijer PR, Gold CS, Gowen SR (1994) Occurrence, distribution and abundance of plant Speijer PR, Gold CS, Karamura EB, Kashaija IN parasitic nematodes on bananas in Uganda. (1994b) Banana weevil and nematode Preliminary results of a diagnostic survey. Afr J distribution patterns in Highland banana systems Crop Sci 2 (1) , 99-104 in Uganda: preliminary results from a diagnostic survey. ln: Proceedings of the First International Mukandala LG, Ndile MR, Sentozi E, Bosch CH Crop Science Conference for Eastern and (1994) Planning of participatory research in SouthernAfrica, Makerere University, Kampala, Ntoija, Bukoba District. Amsterdam, the Nether­ Uganda, 14-18 June 1993, Adipala E, Bekunda lands, Agricultural Research lnstitute (ARI) and . MA, Tenywa JS, Ogenga-Latigo MW, Mugah JO Maruku Bukoba and Royal Tropical lnst1tute (eds) , 1, 285-289 (KIT) , Tanzania Field Note no 46, Tanzania/ Netherlands Farming Systems Research ProJect, Walker PT, Hebblethwaite MJ, Bridge J (1984) Project Lake Zone, 33 p for banana pest contrai and improvement in Tanzania, St Albans, UK, Tropical Development Price NS ( 1994) Field trial evaluation of Musa varieties and Research lnstitute and Commonwealth and other crops as hasts of Pratylenchus lnstitute of Parasitology, EEC report for the goodeyi in Cameroon. Afro-Asian J Nematol 4 government of Tanzania, 129 p (1) , 11-16 Raid J, Raid K (1975) Rural organization in Bukoba District, Tanzania. Uppsala, Sweden, SIAS, 122 p

222 Fruits, vol 51 (4) KHEDER BOULAHIA ET AL

3 ans et appartenant à un agriculteur privé. Trois introduction produits insecticides, dont l'un utilisé à deux doses, ont été testés par rapport à un lot d'arbres Récemment, ]ERRAYA et ZAIDI (1995) ont mon­ tré que la ruineusedes agrumes, bien que d'intro­ témoins non traités ; l'essai a donc été constitué duction récente en Tu nisie, provoquait des dégâts de quatre traitements et un témoin. Cinquante sévères sur les pousses estivales de diverses espèces pieds, dix par traitement, ont été choisis dans le du genre Citrus. Les traitements appliqués en cette verger expérimenté. saison (été), à titre d'essai, n'ont pas pu assurer Les produits appliqués ont été les suivants : une protection satisfaisante des organes vulnéra­ - l'Evisect S est un produit présenté sous une bles, en raison, sans doute, de la présence con­ formulation de poudre à 50 % de matière active jointe, dans des proportions comparables, de sta­ (thiocyclamhydrogen oxalate); il agit par contact, des jeunes et âgés de l'insecte nuisible, ces derniers ingestion et est doué de propriétés systémiques ; stades étant les moins sensibles aux insecticides cet insecticide spécifiquea peu d'effetsur la faune employés. auxiliaire ; deux doses ont été choisies : 100 et Le peu d'efficacité relative de la lutte chimique 200 g/hl; pourrait aussi être lié au fait que l'insecticide - le Confidor est un produit commercial qui se induit un taux de mortalité insuffisant lorsque présente sous une formeliquide à 20 % de matière l'insecte nuisible est présent à de fortesdensités ; active (Imidacloprid) ; il agit par contact, inges­ en effet, en cas d'attaque importante, les parasites tion et par voie systémique ; il a la propriété survivants, dont l'espèce se reproduit à un rythme d'avoir un effet remontant ; cela constitue un rapide, restent à un niveau suffisamment élevé avantage tout particulier pour la lutte contre la pour reconstituer la population initiale. ruineuse, puisque un tel traitement assurerait, pendant une quinzaine de jours environ, une De plus, la difficulté des produits à pénétrer la protection des jeunes feuilles, au furet à mesure cuticule foliaire peut intervenir pour expliquer, de leur apparition ; le produit a été testé à la dose également, le peu de résultats obtenus, car, en de 60 ml/hl; freinant la pénétration de l'insecticide dans le - l'Oleostec est une huile minérale émulsionna­ système vasculaire, elle favorise, du fait de la ble, de masse volumique 0,871 et de viscosité 14,8 croissance continue des feuilles, la dilution de la (à 40 °C), à base de paraffine; ce produit permet matière active dans le végétal hôte ; par ailleurs, d'inhiber la ponte de Phylfocnistiscitr ellaet de tuer les nouvelles pousses qui apparaissent après le les larves par suffocation,tout en ayant un coût/ha traitement insecticide restent totalement vulné­ relativement faible, et peu d'effetssecondaires sur rables. Ainsi, la lutte conventionnelle, qui est l'environnement (BEATTIE, 1990a et 1990b). La pratiquée pour le contrôle de la ruineuse des dose utilisée lors de l'essai a été de 500 ml/hl. agrumes, présente de réelles limites. La solution pourrait résider dans la combinaison de plusieurs Un premier contrôle, réalisé le 24 janvier 1996, procédés de lutte (lune biologique, techniques juste avant le traitement, a montré que tous les culturales appropriées, etc). stades de l'insecte étaient présents dans le verger, De telles méthodes n'étant pas encore dévelop­ y compris le stade nymphe, avec, cependant, une pées, la lutte chimique pourrait être améliorée par prédominance de jeunes larves (tableau la). Le la définition d'une gamme de produits efficaces taux d'infestation était alors relativement élevé et peu coûteux, susceptibles d'épargner quelque (tableau Ib: 73 %), avec une moyenne de plus de peu les autres espèces animales utiles. C'est dans deux individus vivants par feuille attaquée (ta­ cette perspective que s'inscrivent les expérimen­ bleau Ic), ce qui justifiait de déclencher un trai­ tations présentées dans ce document. tement chimique. Les applications d'insecticides ont donc été effec­ tuées ce même jour (24 janvier 1996) ; 2 1 de matériel et méthodes bouillie par arbre, quantité qui était jugée suffi­ [expérimentation a été menée sur le site de Mor­ sante pour mouiller les organes sensibles de la nag (banlieue-sud de Tu nis), dans une jeune plan­ plante, ont été apportés à l'aide d'un pulvérisateur tation de citronniers, de la variété Eureka, âgés de à dos, de capacité 18 1.

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