Page 9 - AWA Vol.36-No.5

CROP PROTECTION

problem and not surprising since the spective of its scientific name the fungal Damping-off disease in the
same fungus causes the ‘same’ disease pathogen is responsible for a seriously cashew nursery
in wide range of other tropical fruit tree damaging disease of the branches. This
crops including mango, avocado and pa- initially shows as white patches on the Poor drainage causing excessively wet
paya. Symptoms of anthracnose are wa- bark and subsequently as silky, white and humid conditions in the nursery can
ter-soaked lesions on the leaves, twigs, film of fungal mycelium during the cause severe losses of seedling trees
flowers and young cashew apples, and monsoon or rainy season. Later formed from damping off disease caused by the
which subsequently develop into or- salmon-pink-coloured fungal growth wet-loving fungus-like pathogens Phy-
ange-brown or red lesions. Other wide represents the advanced stage of infec- tophthora species and Pythium species.
ranging and specific symptoms include tion and disease development, with the The delicate, recently-emerged seed-
black spots on the inflorescences, abor- affected bark splitting and peeling from lings are easily killed by these patho-
tion of the flowers and black lesions on the branches, and affected shoots dying gens which infect and attack both the
the nuts. back from the tips. stem/root collar region and root system.
Effective control is achieved by watering
Pink disease is notoriously difficult to
control and partly because it affects so the seedling beds or polybags with a
many other trees – rubber, cocoa, coffee, suspension of cuprous oxide as a wetta-
tea, citrus, mango and nutmeg, thus mak- ble powder or water dispersible granule
ing cross-infection between different formulation in water.
trees a major concern for growers. Best Black mould on cashew
initial response is prompt cultural con- in Brazil
trol by frequent pruning of the affected
shoots and branches. The cut is made Black mould disease caused by the ob-
behind the infected area and ideally ligate parasite fungus Pilgeriella anacar-
when the disease is at its earliest stages, dii is little known outside of South Amer-
followed by burning of the pruned off ica. However, it can cause huge losses in
Spreading branches of branches. cashew nut yield (up to 33 per cent) in
the cashew tree form the However, to be anywhere near effec- the coastal regions of north-eastern Bra-
characteristically dome-shaped tive pruning should be carried out in zil one of the most important areas of ca-
tree canopy (Picture courtesy conjunction with the use of a copper- shew production in the world. The fungal
Nick Ashton-Jones). containing fungicide such as cuprous pathogen grows profusely on the abaxial
oxide. Exposed cut ends of the branches (lower) leaf surface to form a black-co-
should be sealed with a ‘canker paint’ loured layer of fungal mycelium and fun-
Anthracnose disease is favoured by containing cuprous oxide. And by also gal fruiting bodies from which the com-
high rainfall and high humidity, the very carrying out prophylactic spraying of mon name is derived. Pathogen entry is
conditions experienced in a typical ca- the trees with cuprous oxide fungicide through the stomata to impede gaseous
shew growing region for at least part of before the onset of the monsoon or rainy exchange and reduce leaf and shoot
the year. Anthracnose disease of cashew season, and again when the wet season growth. First symptoms are chlorotic
is controlled by using protectant sprays period has ended. spots on the adaxial (upper) leaf surface
of a copper-based fungicide such as cu- followed by dark-coloured fungal colo-
prous oxide, applied to disease suscep- nies forming on the abaxial leaf surface
tible parts of plant. Whole canopy foliar with a velvet-like appearance. Resistant
sprays of cuprous oxide fungicide should cashew clones are available, but foliar
be applied when flower buds begin spray application of a fixed copper fun-
to expand and subsequently repeated gicide is traditionally used by farmers to
through to fruit set. Good spray deposit control the disease.
coverage before onset of the rainy sea- Circle 6 on enquiry card
son is essential to protect against this
disease which thrives when there is
surface water on leaves and other plant ADVERTISE
parts and is coupled with extended peri-
ods of high humidity. IN THE ARAB
Pink disease in cashew, WORLD
just one host among many
Pink disease is another widespread AGRIBUSINESS
and potentially serious disease of ca- Close up, the foliar canopy MAGAZINE AND
shew caused by a basidiomycete fun- appears quite dense but in
gus recently renamed Phanerochaete reality the leaves are thinly borne PROMOTE YOUR
salmonicolor having previously been and generally restricted to the
called Erythricium salmonicolor and branch ends. PRODUCTS
before that Corticium salmonicolor. Irre-
Vol. 36 No. 5 7

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