CASSAVA (Manihot esculenta Crantz) is the main root crop grown in Guyana. The tubers are a popular domestic nutriment and are the staple food for the hinterland communities. Cassava is classified bitter or sweet and is widely adapted for cultivation on various ecological zones. It is a low input crop and is drought tolerant. In Guyana, the commodity is used mainly for food as it is a great energy source. There are more than 30 varieties of Cassava grown in Guyana. Some of which include Four Month, Brancha, Butterstick, Uncle Mack, M Mex 59, Mex 52 and Bad Woman. However, the most common varieties used for cooking are Uncle Mack and Butterstick.
Cassava is becoming increasingly more important as a staple food crop as it can grow reasonably well in infertile light-textured soils, where many other crops would fail. This is because cassava is very tolerant of acid soils with low pH and high levels of exchangeable Al. However, land preparation is a key component to ensure crop productivity. Land preparation should be deep enough to accommodate the tubers of cassava. Since the crop cannot withstand waterlogged conditions, there should be adequate drainage. Soils should be ploughed and harrowed and adequate drains should be made. In conditions where there are lighter soils, flat planting can be done, as opposed to ridging in heavier soils to facilitate drainage. There are various methods of planting Cassava namely, horizontal, vertical and inclined planting.
Pest and Disease:
Correct identification of the pest and an understanding of its behaviour, including its most vulnerable stage would provide insight into its management and control. Here are a few pest and diseases which attack the cassava plant.
Cassava Mealy Bug: Mealey Bug damages the cassava plant during feeding by sucking the plant sap from the leaves, roots, petioles and fruit. This may result in whole plant dieback, dwarfing, seedling blight and plant deformation. Leaves may show symptoms of abnormal colours, forms, leaf fall, wilting, or may appear yellow or dead with honeydew or sooty mould covering the leaves. Plant stems and growing point may have witches’ broom appearance, stunting, dieback and distortion. Plant roots may have a reduced root system.
There are several cultural and biological methods which can be employed to treat mealy bugs attack. Field sanitation and crop rotation are forms of cultural control, while, the use of natural enemies such as predators, parasitoids and parasites such as Ladybugs are suitable biological control methods.
White Flies: These insects are in fact bugs. The adults are a white, moth-like insect that flies upwards from the plant when disturbed. They are about 2mm in length and their wings are covered with a white waxy powder. White Flies can also be controlled using cultural and chemical methods. An integrated control strategy is necessary for the effective management of this pest which includes good farm sanitation. Several new generations of insecticides are now available for the control of whiteflies. Soap based products which target both nymphs and adults should be applied very early in the morning or late in the evening. Other chemicals which can be used include Admire, Pegasus and or Basudin/Vydate L at 10mls to 4500mls water.
Aphids: Aphids attack the cassava plants at all stages of growth and are usually found in dense clusters on the undersurface of the young leaves thus causing leaf distortion. In several cases, aphids cause the leaves to become chlorotic, followed by wilting. Aphids secrete a sweet substance known as “honeydew” while they feed. This substance attracts ants and serves as a substrate for sooty mould (black fungus) thus impairing photosynthesis. Aphids also serve vector for viruses. A contact or stomach insecticide may be used such as Fastac, Decis or Karate at 6mls of 4500mls of water, Sevin 85% W.P. (Carbary) at 6 grams to 4500mls water or Malathion 57% E.C. at 15mls to 4500mls water. Sprays should be directed to underside/surface of leaves.
Cassava Hornworm: Hornworm eggs when deposited on the upper or lower leaves hatch within seven days. The larvae feed for three to four weeks until they mature on young leaves and growing shoot of the cassava plant by stripping away the foliage. In severe cases, the larva can defoliate the whole plant and the entire crop. Controlling breakout of larva can be achieved by spraying Bacillus thuringiensis (BT) on susceptible plants before they become a major problem. Braconid wasp parasitizes cassava hornworms and other insects thereby reducing the population
Cassava Mosaic Disease: This is caused by a virus which is usually present in the plant leaves and stems. Plant leaves infected by the virus usually appear discoloured with mixes of light green, dark green, yellow (chlorotic) and white colour. In severe attack, the leaves become small and stunted and are evident in younger plants. The cassava mosaic virus is spread by whitefly from infested plants to healthy cassava plants. Infested stem cuttings are sources of contamination if used to plant clean fields.
Cassava Bacterial Blight: This is caused by a bacterium which is present inside Cassava leaves and stems. Cassava bacterial blight disease is more severe in young plants.
It appears as water-soaked lesions on cassava leaves and is usually present between leaf veins and is most evident on the lower surface of the leaves. Lesions are small, irregular in shape, with few angles at the edges. The main sources of the bacteria are infested Cassava plants, dead stem and leaves which remain after root harvest. The bacterium enters the cassava plants through wounds on the stems and leaves. There it multiplies in large numbers. Insects can also transfer the pathogen to healthy plants. Cassava bacterial blight is spread by planting infested stem cuttings. Fastac, Decis or Karate may be used for vector control, while, it is advised that farm tools should be cleaned using a bleach solution after they were used to cut infested cassava plants. This is to prevent bacteria from spreading to other plants.
Cassava Root Rot Disease: Cassava root rot disease is caused by microorganisms both fungi and bacteria living on or in the soil. In poorly drained soils, where there is a prolonged wet period, the damage caused by these microorganisms may be greater.
The leaves on cassava plants affected by root disease turn brown, wilted, and the plant appears scorched. Root rot diseases kill both feeder and storage roots of cassava. Cassava root rot microorganisms are spread by water to new cassava roots. Infested plant debris remaining in fields may serve as a source of infecting new plants. The pathogens may also be transmitted through wounds caused by pests or farming tools.
Cassava is an important food supply to Guyanese and much has been done by NAREI to ensure farmers receive the much-needed support. The Institute continues to provide technical assistance to farmers across Guyana ranging from extension services which are free of cost, soil testing, providing cassava sticks and ants baits to affected farmers and farming groups. In 2016, NAREI introduced the usage of bio-stimulants which can aid significantly in increasing cassava yields.