Army worm attack on lucern in upper Sindh
It is higher in feeding value than all other commonly grown fodder crops and it produces about twice as much digestible protein as clover, and about four times as much as grass.
Besides, lucern’s (medicago sativa) capacity to produce heavy yields of high quality feed, its ability to improve soil is widely recognized. Lucern contributes nitrogen and organic matter to the soil, increases filtration rates and improves soil structure and fertility. Lucern is a perennial crop and usually remains in the field for continuously 4 to 6 years. The review of literature has indicated that in some part of the USA the crop remained continuously for 25 years and in Peru it remained for 10 to 20 years.
In upper Sindh, shortage of irrigation water has made this crop very lucrative. Presently, a maund of lucern fodder fetches Rs35 to Rs40 in the local market of Khairpur/Sukkur. The extent of acreage under lucern crop could be gauged from the fact that presently about 40 per cent area under date-palm orchards holds lucern cultivation. As a matter of fact the shortage of irrigation water has tempted growers to undertake cultivation of this previous fodder as an inter crop with the orchards, particularly.
However, it would be proper to mention that the lucern ecosystem is unique among the field crop system in that it represents a relatively long lasting well-established perennial system. This creates many sub-systems and interactions of these with other specific system. A field of lucern (alfalfa) supports a wide variety of insects. These includes insects destructive to lucern or other crops, pollinating insects etc.
Since early sown lucern fodder fetches good price in the local market poor innocent growers started sowing it in October instead of its recommended sowing period of November when winter temperature falls down, considerably. But unfortunately, temperature did not fall considerably and this proved lethal for the entire lucern cultivation sown during the month of October or in the first week of November. This is because the temperature rise allowed the pupal army worm population to emerge into moth in the cotton area of district Ghotki which had encountered widespread army worm attack during the Kharif 2001 season. Since moth of army worm (Spodoptera sp.) has the capacity to take longer flight after the emergence it is likely that the population of army worm which invaded lucern crop in the upper Sindh, particularly in district Khairpur, Sukkur and Ghotki was from the same stock. As a matter of fact apprehension has been expressed on the army worm invasion on wheat 2001-02 at the time of milky to grain formation stage of this crop as experienced during 1996 based on life cycle of the army worm. But probably delayed arrival of winter this year disrupted the life cycle of this menace, an October sown lucern crop in this way came under the crossfire causing colossal loss to the poor growers of upper Sindh.
A survey undertaken during the second fortnight of December has indicated that those lucern field which sustained severe damage by the army worm was mainly those sown early and were under the shade of trees or under the date-palm orchards. In district Khairpur worst affected areas, as observed, were Babarlo, Garhi Mori, Faizwah, Shah Ladhani, Thehri, Rameja, Palh, Noorari, Bhurgari etc. In district Sukkur a 40-acre block under lucern crop was almost wiped out by the invading larvae of army worm. As per various report damage to vegetable and lucern in district Ghotki was rampant from mid November to mid December. As per conservative estimate in total over 2000 acres of lucern and vegetable has been damaged by the army worm in the aforementioned districts of upper Sindh.
The army worm is also known as cut worms. As per study undertaken by various research workers in the country there are six species of army worm in Pakistan out of which most common are Spodoptera litura, Sodoptera exigua and Agrotis sp. They may often be found by thousands in fields and because of their habit of feeding at night, their presence is generally not suspected until the crop is nearly destroyed. When the food supply becomes exhausted in the fields where they have hatched, these caterpillars move out in band of armies and attack crops in nearby fields.
Plant protection measures: When inquired it was apprised by the affected growers that none of the pesticide sprayed for army worm control proved effective.
Suggestions: 1. Farmers in general have left the army worm attacked field abandoned. In view of shortage of irrigation water flooding of affected lucern crop field may not be possible. Since the army worm invasion area harbour advanced stage army worm larvae, as well as pupal population in abundance, it is imperative to give through ploughing of the affected lucern crop fields, as well as grasses in the vicinity to expose the larvae and pupae to birds and other predators.
2. Since ploughing/flooding may not ensure destruction of all hibernating army worm residual population, large scale emergence of moths during the month of March is apprehended. As wheat crop is also the major host of army worm it is warranted that the standing wheat crop in the upper sindh region may be taken under regular pests surveillance both at the provincial and the federal level for timely control of this menace. It would be proper to mention here that wheat crop at milky to grain formation stage has been found very much susceptible to army worm attack particularly, Inqalab variety of wheat which holds large acreage in the upper Sindh region.