Field Pests and Diseases of Cassava

Root, Tuber and Other Food Crops Programme

PESTS

Cassava Hornworm (Erinnyis Ello)

This is considered the most important pest of cassava. It generally occurs at the beginning of the rains.

Damage is caused mainly by the larva (worm), large populations of which can defoliate large acreages of cassava plants on a short time.

The adult female is nocturnal and lays eggs on the leaf surfaces.

Larvae vary in colour (green, yellow, black, etc). They feed on the leaves and migrate to the soil at the time of pupation. The pupae remain in the soil until adulthood.

Control

Dipterex (2g a.i./L water) is effective against the larvae, however care should be taken to avoid harming beneficial insects.

Sound agronomic practices (weed control and good land preparation) reduce adult and pupa populations.

Cassava Mites (Mononychellus tanajoa)

Cassava mites develop on the upper parts of the plant, from the growing point to the green portions of the stem. Mites generally attack during the dry season. Damage begins as yellow spots on the leaves. The leaves lose their green colour and become deformed. Severe damage stunts plant growth and induces branching

Another species of mites, Tetranychgus urticae, attacks the mature leaves at the base of the plant and move upward. Damage begins as spotting that becomes reddish brown. Defoliation occurs and if dry conditions persist plants may die.

Control

	A combination of resistant varieties and application of selective chemicals should be used.
	Chemicals that do not affect beneficial insects should be used.
	Host plants should be uprooted and destroyed.
	The application of water under pressure can reduce mite populations.

Thrips (Frankliniella Williamsi)

Thrip damage the growing point of the plant. Young leaves are distorted and deformed, with irregular yellow spotting. Internodes are usually shortened and in some instances the growing points die, thus inducing lateral shoot growth.

Thrips damage is frequent during dry periods. Plants may recover at the beginning of the rains when thrip populations decrease.

Control

	Best control is had through the use of resistant varieties.
	Systematic insecticides such as Dimethoate (1-1.5 cc a.i./L of water) give good control.

Gall Midges (Jatrophobia Brasiliensis)

Galls are induced on the leaves of the cassava plant by several species of small flies. These lay their eggs on the upper leaf surfaces. The larvae cause abnormal cell growth forming galls. When the galls are opened the larvae can be seen. The galls are yellowish green to red in colour.

Control

	Gall midges are of little economic importance, and therefore do not require control.
	In cases of severe outbreaks in young plants growth may be retarded. To reduce the number of gall infested leaves, leaves may be collected and burnt at regular (weekly) intervals.

DISEASES

African Mosiac Virus (Casual agent unknown)

This disease has never been recorded in Guyana. As the name suggests it is common to the continent of Africa and it is for this reason that planting material from Africa is not introduced to Guyana.

African mosaic is spread by insects (white-flies). The young diseased plants have yellowish areas and frequent leaf deformation. The sizes of young leaves are reduced in adult plants.

All cuttings from infected plants produce diseased plants.

Control

	Use resistant cultivars.
	Use cuttings from disease free plants in areas affected by this disease.
	Do not introduce cuttings from the continent of Africa to Guyana.
	If you suspect the disease is present contact your extension officer immediately.

Cassava Stem Rot (various pathogens )

The cassava stem, which is normally used as planting material, is attacked by various pathogens.

The infected areas are generally of a different color from healthy stem. Damage begins as superficial rotting which progresses into fruiting bodies of the pathogens appearing on the stems.

This rot is common at the end of the rainy season and in cuttings that have been stored under high relative humidity for lengthy periods.

Control

Avoid planting stem cuttings with symptoms of any disease.

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