BANANA AND PLANTAIN - Tropical Fruits - page 209

Disease and pest management
Diseases
Fruit diseases can cause severe problems if not controlled (Table 8.5). The
most virulent disease of banana and plantain is black Sigatoka, which is
found worldwide, except for subtropical areas or tropical areas where it does
not rain and in the Caribbean. Sigatoka disease has two forms: the yellow,
caused by Mycosphaerella musicola and this form is more prevalent in cooler
areas, and black Sigatoka or black leaf streak, which is a much more virulent
type caused by Mycosphaerella fi jiensis . Both alter the photosynthesizing
capacity of the leaf because they produce necrosis that can extend to the
whole leaf area, and at the same time there is an induction for premature
ripening of the fruit because of more ethylene being released by the infected
leaves, thus reducing calipers and yields. Control in intensive production
systems relies on the use of fungicides, which have to be rotated and are
very expensive, increasing the production costs signifi cantly. Therefore, this
approach may not provide a long-term solution for small growers and others
serving local markets.
One way to reduce fungicide costs, which in intensive production systems
can account for 25-30% of the production costs, is to use disease forecasting,
which is based on the evaluation of climatic conditions and calculating
the stage of evolution of the disease (SED). The idea is to spray as soon as it
is considered necessary with a strong systemic fungicide mixed with pure
mineral oil and rotate products with dif erent modes of action to reduce
fungicide resistance development. This approach has reduced the 40-60
applications per year to 12-14. Biofungicides have been tried, but in high
disease pressure areas they do not work well, but they can be combined with
contact fungicides, allowing reduction of the rates that are presently used.
Eliminating the necrotic leaves or parts of the leaf is another practice to reduce
dispersion of conidia and ascospores. Breeding for resistance is essential, using
natural resistance in other banana varieties, or biotechnology to transfer
resistance will probably provide a long-term solution.
Fusarium wilt (Panama disease) has caused severe disruption of banana
and plantain production where susceptible cultivars, such as 'Gros Michel',
are grown; fortunately, resistant genotypes do exist, but the fungus can
also mutate and eventually af ect them. The two other major diseases are
the bacterial disease 'Moko' and the viral bunchy-top disease. For 'Moko'
prevention is the best strategy, consisting of isolating and eradicating any
infected plant and its neighbours and having tools used for cutting in the
plant, especially the machetes used for desuckering, disinfected after each cut
with Vanodine™ or a similar product.
Preharvest diseases, including fruit freckle ( Phyllostictina musarum ) and
speckle ( Deightoniella torulosa ), can cause fruit skin spotting. 'Cigar-end rot' is
associated with Verticillium theobromae and Trachyspharea frutigena , infecting