Growing cassava in Guyana - Narei

Cassava Bacterial BlightInitially, damage by cassava bacterialblight appears as water-soaked lesions.Eventually the leaf blades turn brownwith the water soaked areas at theleading edge of the brown patch. Thedisease is spread by planting stemcuttings from infected plants. Someinsects are also responsible for transferringpathogens to healthy plants. It istherefore advisable to use disease free planting materials. Additionally,vectors can be controlled using Fastac, Decis or Karateat the recommended rate.Cassava Bud NecrosisThis disease is caused by a funguswhich occurs on the surface of stemsand leaves. This disease appears aspatches of brown or grey fungalcovering of the stem. The fungalmatter covers buds which reducestheir sprouting ability. A fungalsolution could be sprayed for control.Additionally, farm tools thatare used to cut infected cassava plants should be cleaned with ableach solution often to prevent the fungus from spreading toother plants.Leaf Spot DiseaseThe leaf spot diseases are caused by fungi and appear as lesionson the upper surfaces of leaves. Leaf spot diseases spread to newplants by wind or rain. A fungal solution could be applied tocontrol this disease.Cassava white leafspotCassava brown leafspotsymptom of cassavaBacterial BlightCassava bud necrosisCassava leaf blightCassava Root RotThese diseases are caused by fungiliving on or in the soil, especially inpoorly drained soils. The leaves oncassava plants affected by root rotdisease turn brown, wilt and theplant appears scorched. The storageroots may swell unusually and developlight brown discolouration. Theroots may give out a bad smell asthey rot. This disease can be controlledby burning plant debris in infected farms and with the useof disease free planting materials. Spraying infected plants witha fungal solution is also recommended.Harvesting and StorageTime after planting is a commonly used index for determiningwhen to harvest cassava. This is dependent alsoon the variety planted. Generally, roots are typicallysufficiently well-developed beginning six to seven monthsafter planting.In Guyana, harvesting is done by hand and is easierwhen the soil is moist. To facilitate lifting of the roots outof the ground, the main stem of the plant is usually cutback to a height of 30cm to 50cm (12-20”). The stem isused as a handle to lift the roots out of the ground.While lifting, care should be taken not to break the rootsor split the skin.After the roots have been pulled out of the ground, theyare removed from the base of the plant by hand. Caremust be taken during the harvestingprocess to minimize damage to the roots.Mechanical damage incurred by theroots during harvest will result in higheramounts of postharvest moisture loss andsecondary decay.Harvested cassava should be placed inwell ventilated field containers for transportout of the field. It is preferable touse wooden crates or strong plastic containers(sacks or bamboo baskets are notrecommended).Roots intended for storage should be properly curedimmediately after harvest. Cassava can be cured outdoorsif piled in a partially shaded area. Cut grasses orstraw can be used as insulating materials and the pileshould be covered with canvas, burlap or woven grassmats. Curing requires high temperature and high relativehumidity (RH), and this covering will trap selfgeneratedheat and moisture. The stack should be leftundisturbed for about four days. Cassava can also becured inside a protected structure at ambient temperature,provided the (RH) is high. Wetting the floor orusing a small electric humidifier can obtain a high RH.The simplest means of preserving cassava is to delayharvesting and allow the roots to remain in the ground.However, cassava roots will become fibrous and woodywith prolonged in-ground storage time and flavour maybe impaired. Also, the longer the roots remain in theground the more risk there is of insect, disease, or rodentattack. Harvested roots can also be stored in the groundburied in trenches or holes filled with a sand/soil mix.Another method of storing cassava is to place them inwooden crates containing damp sawdust. However, ifthe sawdust is too moist it promotes fungal growth andif it is too dry the roots deteriorate quickly. Lining thecrates with perforated plastic prevents dehydration ofthe sawdust, resulting in a storage life of about onemonth. Cassava roots treated with the fungicideThiabendazole can be stored for 3 weeks inside perforatedplastic bags at ambient temperatures. Keepingthe roots inside plastic bags also reduces the incidence ofFor further information contact:CEO,National Agricultural Research Iand Extension nstitute,Mon Repos, ECD.Tel: 220-2249/ 2843Email:insap@guyana.net.gyMinistry of AgricultureNational AgriculturalResearch and Extension InstituteGROWING CASSAVAIN GUYANA

Cassava is the main root crop grown in Guyana. The tubersare a popular domestic food and are the staple foodfor the hinterland communities. In Guyana, cassava is classifiedas bitter or sweet. Cassava is widely adopted for cultivationon various ecological zones and it is known to be adrought tolerant, low input crop.Cassava is used locally for food by boiling. Some amountsare processed in flour, farine, cassava bread, cassareep, andalchoholic beverages.. Cassava can also be utilized as aningredient in animal feed.The Ministry of Agriculture has recognized the importanceof cassava both from a food security standpoint as well as acrop for value-added products. Recently the Ministry hasjoined the Latin America Consortium for cassava, CLA-YUCA, to give impetus to further enhancing the cassavaindustry in Guyana.VarietiesINTRODUCTIONIt is estimated that there are in excess of 30 varieties ofcassava grown in Guyana. Some of these are Four Month,Brancha, Butterstick, Uncle Mack, M Mex 59, Mex 52 andBad Woman. The two most common varieties used forcooking are Uncle Mack and Butterstick.Land Preparation and PlantingCassava can be grown on a wide range of soils but preferslight deep soils that encourage tuber development. Landpreparation should be deep enough to accommodate thetubers. Since the crop cannot withstand waterlogged conditions,there should be adequate drainage. Soils should beploughed and harrowed and adequate drains made. Forlighter soils, flat planting can be done. In heavier soils, however,ridging may be necessary to facilitate drainage.The planting materials for cassava are the stems of matureplants. The material may be planted immediately afterharvest or can be stored for up to six months. If the materialis to be stored, it should be placed on bundles andstored in the shade. Alternatively the sticks could be bundledand placed upright under shade.Before planting, the material should be cut into piecesabout 20-30cm (8-12”) long. In order to control pests duringinitial period of growth, planting materials should besoaked in insecticidal solution for approximately 10 minutes.The insecticides recommended are Triazophos(6ml/gal water) or Diazinon (10ml/gal/water). The cuttingsshould be planted vertically into the soil. The recommendedplanting distances are 0.9m (35”) between rowsand 0.9m (35”) within rows. This results in about 1,235plants/ha (5,000 plants acre).FertilizersMost soils in Guyana are acidic but cassava seems tolerantto these soils. As a general rule before applying fertilizers,the soils should be analyzed to determine the types andamounts to be sued. If a soils analysis is not done the followingrates of fertilizer elements may be applied.Nitrogen 68 kg/haPhosphorus 100 kg/haPotassium 150 kg/haPest ManagementCassava MealybugThis pest causes leaf loss and weakens the stem plantingmaterial. Infected leaves will exhibitabnormal colour and eventually wilt.The recommended method of controlis to use natural enemies such as theladybirds. Alternatively, controllingants which help to spread the mealybugsby spraying with Basudin can bepracticed.WhitefliesThese pests are generally foundon the undersides of leaves. Theysuck sap from the leaves resultingin leaves becoming mottled,yellow and brown before drying.Chemicals recommended forcontrolling whiteflies includeAdmire, Pegasus, Basudin orVydate L at 10ml to 4500 ml of water.AphidsAphids are found as clusters on the undersurface of theyoung leaves and also on youngtender stems and growing point.They suck plant sap causing a generalweakness of the plant. Contactstomach insecticides such as Fastac,Decis, Karate, Sevin or Malathionare recommended for controllingaphids.ThripsThe infestation by thrips is mostsevere during dry periods. Thripssuck saps from leaves which causesthem to lose their colour. Applicationof insecticides such as Regent(Admire), Abamectin and Vydate Lat 5 ml to 4500 mls water, to bothsurfaces of leaves is necessary foreffective control.MitesMites are extremely tiny and appear asdust-like particles on the underside ofleaves. These suck sap, resulting in leavesbecoming yellow and eventually turningreddish.Chemicals such as Abamectin, Newmectin or Vertimec at5ml to 4500 mls of water are recommended for controllingmites.Lace Wing bugsThese bugs are found on the undersurface of leaves. Theirsucking action results in leaf molting.This leads to premature abscissionof leaves. Chemicals recommendedfor control of lace wingbugs are Decis, Karate or Fastac at6mls to 4500mls water.Gall MidgeThis insect causes gall formation on plants. Galls are normallyfound onleaves, buds andstems. Chemicalcontrol can beachieved with thesue of Sevin, Trigard,Diazinon,Admire orMalathion at the Larva and Adult Gall Midgerecommendedrate.Horn WormThe larvae of these worms can devourcassava leaves in one to twodays. Hand picking and squashingof the worms is a recommendedmethod of control. Alternativelycontrolling breakout of these andtheir caterpillars can be achieved byspraying Bt on susceptible plantsbefore caterpillars become a major problem.Acoushi AntsThese ants cut the plantleaves, resulting in completedefoliation. Baiting is the recommendedmethod of control.Disease ManagementCassava Mosaic DiseaseThis disease is caused by a virus whichoccurs inside cassava leaves and stem.Infected leaves become discolouredwith patches of normal green mixedwith lighter green, yellow and whiteareas (chlorosis). Whiteflies are responsiblefpr transmitting this diseaseto the plants. It is therefore necessaryto control whiteflies with the use ofsymptom of cassavamosaic diseaseAdmire, Vydate L, Abamectin or Vertimec at the recommendedrates.