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A deadly undiscovered menace of mango blossom
Mango belongs to Anacardiaceae family of the plant kingdom. There are as many as 39 or even more species of mango (Mangifera indica) genus in South Asia and about 13 of them are cultivated for edible fruits.
The real place of its origin remains shrouded in the antiquity, as it has been in cultivation for almost 4000 years. Pepenoe (1939) classified the mango in two classes: seedling and horticultural varieties. The seedling races are found in Cochin, China, Philippines, West Indies, Cuba, Mexico and Brazil. The latter varieties are cultivated in the different parts of India and Pakistan.
The nomenclature of horticultural varieties is very difficult to understand for the reason that these varieties have been named unsystematically, which means that each variety is associated in some way with a noun, such as the place of its origin, name of the farm’s owner, or the name of the person who liked it most.
According to an estimate, mango is cultivated on 94000 hectares in Pakistan. It is grown mainly in Punjab (65%) and Sindh (37%), where more than 110 varieties of this fruit are produced. Among the most famous are: Sindhri, Daseri, Langra, Anwar Ratol, Chausa, and Lad Badshah.
Pakistan occupies an important position for growing world’s best mango varieties. But unfortunately the yield is very low as compared to other countries, for instance, the average per hectare yield (metric tons) in India is 12000, China yields 2142, Sri Lanka produces 1350 and Pakistan produces 914.
The causes of low yield of mango, besides related to agronomy and hygiene, are the severe attack by the sporadic insect pests and a growing number of diseases.
In Pakistan, reportedly, mango crop is attacked by 86 insect species, of which fruit flies, mango hopper, mango mealy bug, scale insect are widespread. Among the disease most common are mildews, anthracnose, dieback, etc.
In spite of the growing demand for export, no adequate measures are taken, by the authorities, to protect orchards of this precious fruit, especially in Sindh. For the last couple of years mango trees both in Sindh and Punjab are facing a catastrophic disease commonly known as “sudden death” or “quick decline,” but horticultural research institutes are silent to this effect till now.
Similarly, this year mango orchards, in district Khairpur, encountered a new deadly menace, which was observed on mango blossom (inflorescence) causing black spots on the floral axils (raches). Apparent symptom of this disease was like small pox patches on floral axils.
It was observed in the second week of February following sprouting of blossom. Subsequent survey of the mango orchards indicates that the disease continues infecting the inflorescence till fruit bearing.
According to the latest survey (mid March) showed that floral axils having a few black spots survived the attack but holding very little bearing. It is apprehended that the infected axils may not be able to hold the weight of fully developed mangoes and would fall to the ground following wind. The survey also showed that a floral axis having more than 3 or 4 black spots had dried up or born no fruits. Apprehending black spots a floral disease, some growers applied fungicides twice but fungicidal spray failed to control the menace. Survey of mango orchards also indicated that the very menace was not variety specific, however, “Sindhri” variety of mango was found more susceptible to this diease than others. The menace was also found in the district Khairpur. A progressive mango grower of Khairpur, Ijaz Ahmad Phulphoto, informed that he has been observing this menace for the last two to three years but this year it has inflicted severe damage to some trees in his garden as well. As a matter of fact mango orchards in the upper Sindh region as a whole encountered less insect pest and disease problem as compared to lower Sindh.
In upper Sindh, it is only the mango hoppers which requires pesticidal sprays. The hopper nymphs and adults when they suck cell-sap from the inflorescence and tender shoots (the nymphs are particularly harmful as they are voracious feeders), they cause the inflorescence to wither and turn brown. Even if the flowers are fertilized, the subsequent development and fruit setting may cease. Following severe hoppers attack sooty mould develops on patches of honeydew exuded by the nymphs. Young fruits and dried inflorescences break of at the axil and fall to the ground as the wind blows.
Suggestions
1. To ascertain the spread of this new menace of mango blossom it is imperative that a survey of mango orchards both in upper and lower Sindh should be undertaken and farmers are apprised of its control measures.
2. Since major contribution to the economy of Pakistan in the years to come will be our horticultural production especially that of mango. A mango disease diagnostic and research laboratory with facility to test pesticide residue should be built in the country as demanded by Mango Growers’ Association of Pakistan.
The writer is an entomologist, and a freelance contributor to Dawn
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