2[7] Mycosphaerella[ EDFS

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This leaflet is produced by the Ministry of Agriculture & Livestock, Solomon Islands, with support
from IPPSI: Improved Plant Protection in Solomon Islands, a project financed by ACIAR, the
Australian Centre for International Agricultural Research, Canberra. Authors: Helen Tsatsia, MAL &
Grahame Jackson, TerraCircle Inc.

Extension Fact Sheet 2:

Black Sigatoka

Common name: Black Sigatoka or Black leaf streak

Scientific name: Mycosphaerella fijiensis

Hosts

The fungus infects bananas and plantains, Musa species.

Damage

Red-brown streaks appear on the underneath of the third or forth youngest leaf. These
form long spots with grey or light brown centres and dark brown or black margins
(photo, right). The spots join together, often with yellow areas between. The infected
areas often form bands several centimetres wide on either side of the midrib. In severe
infections, spots do not occur, but large areas of the leaf turn black and die. Generally,
the streaks are more common at the tips and edges of the leaves (photo, left).

The effect of the disease is a loss of leaves: leaves die early. Instead of lasting 200

days they last only 50. This reduces yield by 35-50%, depending on severity of the

infection and on the variety. Cavendish varieties are particularly susceptible and these

are grown for sale worldwide. About 30% of the production costs in commercial

plantations are spent on fungicides to control the disease.

The weight of the bunch and the ripening of the fruit are affected by the number of
leaves on the plant: if too few at flowering then bunch weight is low. If less than five
leaves at harvest, the fruits do not ripen properly: they may ripen early.

Biology and Life Cycle

Spores are produced in the dead, grey areas on the upper leaf surface. The fungus has
two type: ascospores and conidia (see diagram

). The ascospores are the most

important. They are released from the upper leaf surface when there is rain or high
humidity. They travel by air currents or rain splash, and land on the underside of the

The diagram of the life cycle is from APSnet Education Center. Back Sigatoka of bananas and plantains. The permission of

The American Phytopathological Society to use this diagram is gratefully acknowledged.
http://www.apsnet.org/education/LessonsPlantPath/BlackSigatoka/default.htm

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emerging leaves. The spores germinate and the germ tubes enter through natural
openings in the leaf. The fungus grows within the leaf, killing plant cells, before
returning to the surface to produce more spores. Different strains of the fungus (plus
and minus) come together to form the sexual stage (see diagram).

Signs and Symptoms

On leaves, a rapid
development of red-brown
and yellow streaks, drying
from the margins back to
the mid-rib, and early
death of leaves, are typical
of this disease.

Management

Cultural control:
Carry out the following
recommended to allow
more air into the
plantation to dry the leaf surface, to prevent infection, or to reduce the number of
spores:
•  Cut off leaves (if more than 50% infected), or cut out parts of leaves;
•  Plant at wide spacings;
•  Weed regularly;
•  Cut out suckers, leaving 3-4 plants of different sizes per plant;
•  Remove and burn old infected leaves;
•  Use a mulch to improve plant health.

Resistant varieties:
Many plantains in Solomon Islands are either resistant or partly resistant to Black
Sigatoka. However, if farmers want to grow varieties with Cavendish qualities for
household use or the market, then they should ask MAL. The Honduran Foundation
of Agricultural Research has bred varieties, e.g., FHIA-1; FHIA-2, FHIA-3. These are
dessert or dessert/cooking bananas with resistance to Black Sigatoka.

Chemical control:
Fungicides are only recommended for commercial plantations, these are:

A) Protectant fungicides:
• dithiocarbamates (e.g., mancozeb);
• Banana misting oil.

B) Systemic fungicides
•  triazoles (e.g, propiconazole and flusilazole);
•  strobilurins (e.g., azoxystrobin).

It is important to rotate the fungicides in the different groups to prevent the build up
of resistant strains of the fungus. In drier times, mancozeb can be used alone.