IN December 2004, the UN’s Food and Agriculture Organization (FAO) issued a warning that Pakistan would be attacked by the locust in March 2005. There were apprehensions that the late sown wheat crop in upper Sindh, especially in the adjoining winter locust breeding areas of Balochistan would be the worst hit. The warning proved futile despite the recent rainfall and prolonged cloudy weather which provide ideal ecological conditions for locust breeding.
Unfortunately, the same conditions allowed the insurgence of armyworm in the semi desert areas of upper Sindh in Khairpur, Sukkur and Ghotki districts. The main victim of locust was the standing wheat crop, especially the late sown, which is still green and in post-milky stage. Due to the late picking of cotton about 40 per cent of wheat area was sown late in December till the first week of January.
The writer, during a survey observed that the wheat area with plenty of trees and greenery harboured more armyworm population as compared to other areas. It also came to the knowledge that as against the TJ-83, Mehran, Kiran, Bhakhar varieties, Inqalab-91 was more susceptible to infestation. The maximum population recorded on this variety at Deh-Karopir in Talauka Salehpat was three larvae per square meter. Almost 90 per cent larvae were in the first and second stages of development (instar).
Regrettably, neither the provincial Agriculture Extension officials nor the growers were aware of this pest insurgence. Armyworm infestation may bring significant yield loss if the natural controlling agent, especially birds like maina and chirhi failed in controlling the menace as spraying of wheat was not undertaken in this area.
To assess other spots, including the kachho areas of Khairpur and Sukkur, a survey was undertaken on March 27 and 28. It was observed that both early and late sown crops were free from the armyworm. The early crop was ready for harvest.
Due to the prolonged rain and cloudy weather, wheat sown as inter-crop with date palm, mango, and citrus orchards sustained moderate to severe damage by aphids. Following a heavy attack the entire wheat fields looked black from the distance. Honey-dew secretion by aphid allows the development of fungus, both on wheat-head and leaves which rendered the crop black.
Notes revealed that armyworm caused major economic damage in semi-arid and arid regions of North America by destroying one million acres of winter wheat in a year, in Montana, alone.
Khairpur, Sukkur and Ghotki districts being semi-arid to arid, it was possible that the susceptibility of Inqalab-91 variety which dominates the wheat crop in upper Sindh might have been the factor behind this outbreak. This carries weight as in mid- 1970’s when Mexican varieties were introduced, armyworm gained prominence as a pest of wheat in India.
Previously, it was considered a minor pest of wheat, sugarcane, maize, jowar, bajra and other graminacious crops. Regarding wheat-head armyworm control, very little work has been. No economic threshold level (ETL) has yet been developed. Reports suggests that trying to control the pest could be a mistake when most of the larvae were nearly full grown, as the damage had already been done.
Accordingly, insecticide treatments worked best while armyworm larvae were small and wheat heads (earheads) still green. To avoid a false alarm, remember that wheat-head armyworm tend to build-up in the field margins. So prior to initiating the control measures, survey of the field is necessary.
