Mango, Mangifera indica L. is one of the most
important foreign currencies earning fruit crop of Pakistan and offers a
wide choice of near about 200 mango varieties. Some of the most famous
varieties are Sindhri, Dasheri, Siroli, Summer Behist Chaunsa, Baganpali,
Swarnarika, Anwar Ratole and Langra. It is known to suffer from a number
of insect pests and diseases caused by different organisms, which
affects different parts of plants, at all stages of growth and
development. No information regarding the extent of damage to the plant
is available, but some of these are certainly responsible for causing
considerable damage and become a limiting factor in many mango-growing
The present situation of mango orchards, with special
reference to the province of Sindh, needs special attention, where about
all mango orchards are suffering due to an unknown disease problem,
causing decline or sudden death of mango trees. At present mostly 3 to 5
and most likely 60 to 85 percent of trees are suffering from this type
of disease, in various mango orchards of Sindh. There are different
opinions of plant disease specialists, but the preliminary studies
carried out on the problem reveal that Asian Ambrosia Beetle is a vector
of a Killer Mango Disease in Sindh. Beetle and disease both could be
controlled through IPM.
Actually Asian Ambrosia Beetle (AAB), Xylosandrus
crassiusculus, has been identified from the various samples taken from
mango orchards of Sindh. This beetle has a stout reddish brown body and
is reported as a pest of woody ornamentals, fruit and nut trees. It
spreads through the movement of infested wood logs/pieces and by its own
movement. These beetles are so tiny; initially, attacked trees do not
show symptoms. The strands can identify infestations as they excavate
galleries into twigs, branches or small trunks due to female beetle
activity, leaving only pencil-lead sized holes in the bark. The Ambrosia
beetles are associated with symbiotic fungi, to which females carry to
the tree. Both adults and grubs of beetle feed on the growing fungi and
on the wood. The tunneling of AAB in trees generally is not as serious
as the effect of the fungi on the plant. The fungi usually darkly stains
the wood of ambrosia-beetle infested tree and may be largely responsible
for plant death. Fusarium species are found predominantly associated but
Fusarium and Rhizoctinia spp. (rotting roots), Diplodia spp (causing
gummosis or stem blight or die back.), Glomerella
cingulata-Colletotrichum gloeosporioides (cause of anthracnose) and
Pestaloptiopsis mangiferae (causing leaf blight) are also found present
in infested samples. It may be considered that beetle along with these
all diseases is responsible for the decline (dying of trees) and the
condition may be termed as 'Disease complex' (presence of more than one
disease causing agent). It may also be proved through presence of the
symptoms of most of these diseases in a single plant at same time.
Isolation of near about all the fungi (causing these diseases) from
diseased specimens collected from same single diseased plant as well as
nature and behaviour of these diseases causing organisms is an other
evidence. Moderate temperature, high relative humidity and weak plants
are main contributing factors in the spread of anthracnose and die back,
while root rot and tip die back caused by Fusarium species develop more
on weak plants, in high soil temperature and drought conditions. It is
also true that dying of trees or decline is generally observed more in
the neglected orchards, which is common factor. The shortage of
irrigation water may also be another main cause, which helps to the
disease causing organisms to grow, develop and spread more.
However, development of small saprophytic white
mushrooms on dried trunk (stem) of diseased trees, rotting of
roots/trunks having very bad smell and small holes on trunk due to
beetles are the most commonly occurring symptoms and are present in
almost all mango orchards.
The growers are going to cut-off/remove diseased
trees from their orchards because they feel no way except destruction of
diseased mango trees whereas, researchers had conducted various
experiments on the control of beetle and diseases of mango plants and
fruits. The preliminary results showed that prevention is the best cure.
They have evaluated various ways by which the diseases can be
controlled. Therefore, it is suggested that integrated pest and disease
management practices must be applied by using different insecticides in
combination with suitable fungicides whereas different cultural
practices may also help to check the problem. It must be kept in mind
that use of insecticides as well as fungicides is not alone source. On
the other hand, it is also pertinent to mention here that the
insecticides and fungicides increase the cost of production. Their use
is risky for the health of worker as well as mango consumer of each age.
These decrease the fruit quality because of their toxic substance
residues that may remain present so much time in the tree and persist in
to the fruit. Therefore, following management principles should be
practiced on top priority basis to cover the risk of environmental
pollution and toxic effect on human being.
1. To keep trees healthy and avoid any
unnecessary stress (drought, injury, nutrition, etc.).
2. As the infested tree plants survive and often
can recover with age, therefore larger spacing in nurseries and orchards
help slow the spread from plant to plant.
3. Only healthy seeds, seedlings and plants
should be used for planting and budding or grafting.
4. Inter cropping, mix cropping, cover cropping
and or multiple cropping in or in the surrounding of mango orchards must
be avoided so that the similar possible pathogens of the sown crop and
mango (both) may not be multiplied and spread in orchards.
5. Irrigation must be applied as per requirement,
but not subject to the availability.
6. Avoid high doses of nitrogen fertilisers, but
apply proper and balanced fertilisers, on the basis of soil type, age
and need of the tree.
7. Proper sanitation of orchards and pruning of
trees (eradication of disease causing organisms through removing and
burning of diseased plants or plant parts) helps to reduce the infection
and growth, development and further spread of beetle and the fungi
causing disease complex situation. Therefore, heavily infested plants or
plant parts should be removed and destroyed. Once attacked, tree becomes
more attractive to female beetles, therefore infested trees must be
removed and burned before completing the life cycle of beetles that
requires 55 days hence it be ensured that the attacked trees should not
be a source of beetles.
8. Easily available broad-spectrum insecticides
in combination with fungicides should only be used when all other ways
become fail. Proper application method with optimum dose must be
confirmed. However, encouraging results could be obtained by consulting
with entomologist and pathologist.