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Black headed caterpillar threatens date palm
Date palm (Phoenix dactylifera) may have been the first, and to some, the most important of all the trees. Its origin is said to be the countries around the Gulf, Iraq, Iran, the Arabian Peninsula and the Turbat-Mekran area of Balochistan.Reportedly Pakistan is the is the fifth largest date producing countries in the world.
Khairpur district in upper Sindh has an ideal climate for date production being hot and dry for most of the year with the minimum of rain. As per conservative estimate, date palm acreage in the district is around 100,000 acres comprising over four million trees. Because of the increasing twin menace of water logging and salinity, the area under date palm is rapidly increasing in the district. This is because date palm tree is more tolerant to saline condition as compared to other crops including fruit trees.
Till a couple of years back when there were no shortage of water in the irrigation canals, and monsoon rain was almost regular and so the underground water table, date palm orchards in the district use to encounter its regular pests such as red palm weevil, scale insect, mites, and termites and occasional fruit borer since 1997. However following absence of rain, and acute shortage of water in the irrigation canals continuously for the last three years a new problem erupted which is now posing a serious threat to the date palm plantation in the Khairpur district.
According to a survey, the very new menace had managed to kill over 8000 trees of different age group till December 2000 in the district. Although no thorough survey of date palm orchards to this effect has been undertaken in the district recently, however, visits to about a dozen of orchards in different talukas of district Khairpur particularly in taluka Gambat and Kingri it was evident that killing of date palm trees by this new menace was unexpected.
Unfortunately, so far several thousand date palm trees, mostly fruit bearing, have been killed by this caterpillar pest but no efforts have been made to curb this menace by the horticulture research wing of the agriculture department government of Sindh so far.
Symptoms of infestation: It has been observed that following infestation of this pest, the fronds (leaves) of the date palm trees starts drying from the lowest part of the leaves. As time passes, the drying of leaves extends upward finally leading to the death of the crown. It will be most appropriate to elucidate that except the drying of leaves no symptoms of attack were visible externally on the leaflets.
However, removal of the base of fronds revealed the presence of black-headed caterpillars feeding upon the sheath, layer after layer. A total of 30 larvae (caterpillars) were collected from a single infested date palm tree, which was about 20 years old. The larvae were of blackish gray colour. The length of a fully-grown larva was 22 mm. Besides, the larvae moved fast and reacted sharply on touch.
The larvae were found feeding upon the soft and sweet sheath, which encircle the base of the frond. The sheath consists of a white connective tissue ramified by vascular bundles. As the fronds grows up, the connective tissue largely disappear leaving the dried (brown) vascular bundles as a band of rough and tough fibres which serve as a venue for pupal formation. Feeding on the white connective tissue by the caterpillars led to drying of fronds halting growth of the date palm and killing of the crown finally.
Suggestions
In order to protect date palm plantation from the ravages of black headed cater pillars agriculture department should launch a campaign with the help of growers for cutting off and burning the fronds that are first attacked.
The campaign should follow the spraying or dusting the bases of the fronds with suitable persistent pesticides. Since pesticide application would be difficult because of height and safety factors and may be harmful in the long run, because of adverse impact upon the natural control agents of this pest it is imperative that biological control of this menace is initiated with the help of PARC.
The writer
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