Frost damage to mango trees
MANGO trees are amongst the most cold sensitive fruit plants and grow best in subtropical and tropical climates. The leaves and twigs of the plant suffer serious damages at temperature below 30 degrees Fahrenheit. Low temperatures cause far more damage to the plant than high temperatures.
Frost damage occurs when ice forms inside the plant tissue and injures plant cells. Freeze damage becomes more extensive when combined with cold winds. This year again mango orchards in the country have witnessed severe cold with frost and freeze damages. The mango growers are afraid the severity of the weather would tell upon the growth of the fruit reducing its production.
In Pakistan, the area under mango cultivation is 167.5 thousand hectares with a production of 1,732 thousand tones being the second major fruit crop of Pakistan after citrus. It ranks fourth in the world for the production of the king of the fruits.
Unfortunately, while mango has emerged as an important exportable commodity, the economic life of groves, productivity, yield and quality is gradually declining.
Resistance to cold in older mango trees is more than young trees. Consequently young mango orchards are suffering serious damages due to cold in mango zone including Multan, Shujaabad, Bahawalpur and mango-growing areas of Sindh.
Mechanical factor to save older trees include bark thickness, furnishing an insulating coat over the susceptible cambium tissues. Young groves less than five years of age have heavily been damaged throughout the mango region of Punjab and Sindh. Tree losses in this age group are ranging from 50-70 per cent. Groves of five to ten year in age have sustained branch damage of two to six feet. Trees of this age group are also showing galls on trunks where damage is happening on bark.
Common types of damage occurring in orchards include: death of dormant flower buds, dieback of trees, and frost damage to tender shoots. Bark in many orchards has curled and is drying with many small cracks. Dead patches of bark are stirring in various locations on limbs and trunk. In young mango orchards twigs and wood have been damaged severely and leaves are rapidly shedding.
Researchers declare that trees loosing leaves rapidly often indicate a good sign and are not at risk, as generally believed by growers. And such trees can revivify quickly. Seriously frozen leaves collapse, dry out, and remain on the tree.
As most growers will testify, it is easy to be affected by frost. And sometimes frost damage is simply unavoidable. When the spoil has occurred, what should be done? The only treatment after a freeze is whitewashing the tree is to delay pruning of frozen and damaged branches until spring or summer to help assess the damage more accurately, and to prevent premature tender growth during the cold season.
The more the pruning is done the more energy the plant expends to heal the wound, thus falling short of energy needed for new growth and flowering. Application of fertiliser should be delayed until new growth occurs in the spring and the amount should be adjusted according to the extent of damage the tree has suffered. If the tree has lost a quarter of its branches to the freeze, quarter less fertiliser should be applied; if the tree has lost half of its limbs, half less should be used.
If the damage is confined to leaves, and the twigs and branches have survived, the amount of fertiliser should be slightly increased. In all cases, frequent light applications should be chosen rather than a heavy dose of fertiliser. High-nitrogen fertilisers should be avoided as they encourage plants to make lots of sappy leafy growth that is particularly susceptible to damage, especially early and late in the year.
Application of a thick mulch helps protect plant roots. The mulch should be removed in the spring when temperatures start to warm up. Mango trees should be watered once a week in fall and it should be continued throughout the winter to keep the tree healthy and vigorous. Cold temperatures can cause a tree to dehydrate quickly, making frost damage more severe.
These problems arise mainly due to non-availability of nutrients in the soil, inefficient use of resources, unawareness about freeze hazards and quality maintenance practices. Still, the farmers are unable to cope with the problems due to their ignorance and lack of facilities involving production management.
It is time the government should take initiatives to educate farmers, formulate policies supporting infrastructural developments, provide access to research repositories and extend facilities at low costs to save the farmers from loss and ensure both qualitative and quantitative production of mango.