Management of Pentalonla nlgronervosa, a vector of banana bunchy top disease in Sindh Province of Pakistan

Abstract

Banana is an important fruit crop in Sindh Province of Pakistan grown over 21,000 ha. Its cultivation was suffering greatly because of banana bunchy top disease caused by banana bunchy top virus. This virus is transmitted by an aphid vector Pentalonia nigronervosa Coq. which got accidentally introduced in Pakistan, resulting in substantial decrease in the area under banana plantations. Studies were carried out to determine the distribution, hosts, seasonal abundance, phenology, natural enemies, possibilities of its cultural and chemical control to develop compact Integrated Pest Management (1PM) program.

P. nigronervosa was recorded from almost all the banana plantations scattered in the middle and lower Sindh areas and in the upper Sindh areas it was recorded up to district Sukkur. Whereas, its infestation was not detected across the river Indus in any plantations surveyed in different districts such as Larkana, Dadu, Shikarpur and Sukkur. However, in district Thatta in the lower Sindh areas, its infestation was detected on both sides of the river Indus,

During the initial survey conducted in 1996, it was recorded from all the banana varieties but its infestation was relatively higher on Dwarf Cavandish followed by William Hybrid. The aphid was more abundant in the lower Sindh areas where up to 85% suckers were infested at Hyderabad, 55.5% at Badin and 49.4% at Thatta. Whereas, in the middle Sindh areas its infestation was low and only 1.5% suckers were found infested at Naushero Feroze. However, during the subsequent surveys, aphid appeared to be spreading north wards and relatively high infestation was detected at Naushero Feroze, Nawabshah, Tharoshah in the middle Sindh areas during 1998 which ultimately spread further north wards and more severe infestation was detected at Khairpur and Sukkur in the upper Sindh areas during 1999.

In the lower and some portion of middle Sindh areas aphid seemed to bred through out the year as all the stages like nymph, winged and wingless adults were available. Whereas, in the upper Sindh areas like Khairpur, aphid underwent some sort of aestivation during summer. Population trends were more or less similar in different parts of the Province. Its population started increasing gradually from September onwards and was maximum in March in the lower and middle Sindh areas and in April next year in the upper Sindh areas. Afterwards, its population started decreasing and was almost negligible in June and July.

Various cultural practices such as sanitation, removal of suckers, hoeing and weeding, fertilizer and irrigation management helped reducing the aphid infestation to a considerable extent. In the plantations where old plant material was destroyed immediately after its removal and suckers were removed in late September and beginning of October, aphid infestation was reduced and ranged from 0.56- 4. 65 colonies/plant compared with 3.69- 11.55 in the adjacent plantations where old plant material was not removed. Similarly, in the plantations where weeding and hoeing was done vigorously twice; once in the end of September and secondly in the beginning of April next year, aphid infestation ranged from 7.50- 9.0/plant compared with 11.25- 14.65 where these practices were not done.

In the banana plantations where application of urea was reduced to half ( one bag of urea used in two equal splits) resulted in the reduction of aphid population to 1.66 colonies/plant compared with 4.95/plant in the adjacent plantation where two bags of urea were applied. Similarly, flooding of banana plantations during the first fortnight of October resulted in considerable reduction in the aphid infestation (0.90-1.50/plant) to 2.45- 5.80/plant where it was not done.

During the survey, an unidentified Hymenopterous parasitoid, a syrphid fly and few predators were recorded associated with aphid colonies. Menochilus sexmaculatus was found to be more promising predator and gave moderate to medium control of aphid in the plantations where its numbers were increased either by redistribution or by conservation.

Spraying of insecticide was found to be ineffective against the banana aphid because they are well protected inside the leaf lamina. Nevacron killed majority (60-75%) of the aphid within ten days after the injection of 0.1 CC solution in the main stem of the banana plant. Whereas, in case of Thymate, mortality was less (25-40%) even after twenty days.