By Dr R.D. Khuhro, Dr S.M. Nizamani, M.M. Jiskani & M.A. Talpur
MANGO tree plant suffers from various insect pests and diseases. Currently, mango trees are dying suddenly at the rate of 2-20 per cent, depending upon the severity of disease and management by the owners of mango orchards.
The Asian ambrosia beetle (ABB) is considered as the primary cause of the mango mortality followed by different species of fungi. Basically, this is a management problem.
The owners of mango gardens give their gardens on contract and forget about its care whereas, contractors don’t apply proper fertilizer, cultural and plant protection practices as required. And the problem of mortality in mango is multiplying. If this, scenario remains, we shall end up with mango cultivation.
Growers have to spend at least 10 per cent of their income on management operations for the sustainability of mango fruit. Garden owners cannot depend on contractors.
The Asian ambrosia beetle (ABB) has stout dark reddish-brown body and is reported as pest on broad host range, including woody ornamentals, fruit and nut trees. The beetle was collected and identified from various samples taken from the dead or the partially dead trees, Shisham, Gold Mohar, Gular, Neem, Eucalyptus, Siris Albizzia lebbek, rubber plant and Casia fistula from various ecological zones of Sindh.
Only females have wings and disperse with small movement from the infested and dead mango trees, wood logs/pieces and by its own short movements. These beetles are so tiny that initially attacked trees, do not show symptoms. In case of severe infestation, the small pin head sized holes appear with the inside and outside movement of beetle on bark.
The beetles excavate galleries in the branches, trunks, roots and twigs. The beetles introduce fungi complex in the mango tree and lay their eggs in clusters. In some mango trees no holes in bark appear but black spots on the basal parts of trunks are present.
After cutting those barks, the light yellow paste with bad odour watery secretion flows. The beetles are also present in infested black basal part of the trunk.
The gum like secretion/drops commonly known as gummosis oozes out from holes of trunks/branches of mango trees infested with beetle. The “C” shaped, legless, white grubs of beetle are found feeding on inner darkened portion of barks. From the infested trunk of the mango tree, the frass of the beetle is pushed out of galleries, in a typical tooth-pick fashion.
Various research experiments have been conducted and are in progress at the Sindh Agriculture University, Tandojam under the Mango Research Project sponsored by the Higher Education Commission, Islamabad. On the basis of these preliminary experimental results, it is suggested to apply sticky traps of one sq. ft. in size by pasting grease on plastic sheets (coated over cloth) at the rate of 10-15 traps per acre at the height of 1-3ft from ground level for catching the winged female beetles. It was observed that green colour sticky trap attracted more female beetles followed by black and other colours.
Regular monitoring of mango gardens for bark beetle and development of decline symptoms is compulsory.
Prune diseased branches along with 4-5 inches of healthy portion with saw and apply bordeaux paste at the rate of 1:1:10 (1kg CuSO4+1kg lime+10 litres of water)on the cut points in July-August.
Removal and burning of diseased/dead mango trees including roots: Avoid wounding the trunks and roots during pruning, inter-culturing and fruit picking. In case of wounds, Bordeaux paste may be applied.
Ploughing/inter-culturing and other sanitation practices should be followed by pruning of gardens in July-August.
Soil testing is compulsory for application of proper chemical fertilizers. Zinc sulphate and other macro and micro nutrients may be incorporated on the basis of soil testing.
Proper irrigation application as and when required but not on the basis of availability of water.
Chemical: Apply Lorsban 40 EC or any other systemic insecticide in combination with Alliete fungicide just after fruit setting.
The same spray may be repeated at the interval of 15-21 days.
Apply 3rd spray in September/October.
Method of application: Generally foliar pesticide is carried out but in this case washing of trunks and branches through spraying or similar to white wash is suggested.
The same pesticides can also be applied by drilling followed by injecting in main trunk and its primary branches deep up to 6”.
