Z Islam and Sheikh Shamiul Haque
61 Coleman Avenue, Toronto, ON, M4C 1P8, Canada
Formerly of Bangladesh Rice Research Institute (BRRI) and International Rice Research Institute (IRRI), now freelance wildlife researcher in collaboration with ICUN and University of Toronto, Canada and Entomology Division, Bangladesh Rice Research Institute, Gazipur 1701, Bangladesh
In the months of April and May 2009 Bangladesh rice production experienced some outbreaks of planthoppers when the most important rice crop of the country (boro rice) was approaching harvest. The boro (dry season) rice is usually grown intensively in about 4.5 million ha and produces about 16-18 million tons.
There has been a history of planthopper outbreaks in Bangladesh. The first hopperburn by brown planthopper was recorded in the 1976 boro season near Dhaka City which affected about 4 ha (Table 1). In the next boro season 20 ha were affected, and by 1978 planthopper damage had increased to 8000 ha in six districts. Hopperburn then spread to other parts of the country, and localized outbreaks became common. Initially, outbreaks were in the boro season while outbreaks started to occur also in the aman season from 1982. The most serious planthopper incidence was recorded in 1983 when widespread outbreaks were reported in 7 districts in boro and 8 districts in aman (monsoon) season.
Table 1. Historical record of planthopper outbreaks in Bangladesh from mid 1970s to end of the century.
|Year||Notes on outbreaks|
|1976||First hopperburn observed in boro season near Dhaka City: 4 ha affected.|
|1977||Outbreaks affected about 20 ha of boro rice in two areas of Dhaka district.|
|1978||Outbreaks in 6 districts in boro season: about 8000 ha affected.|
|1979||Outbreaks in Chittagong and Dhaka districts.|
|1980||Outbreaks in boro season in Dhaka and Chittagong districts.|
|1981||Sporadic outbreaks causing considerable damage in boro season in Dhaka, Comilla, Chittagong and Barisal districts.|
|1982||Outbreaks in boro in Dhaka, Comilla and Chittagong, and in Dhaka and Rangpur districts in aman seasons.|
|1983||Widespread outbreaks in 7 districts in boro, and 8 districts in aman season.|
|1984||Hopperburn in Satkhira, Dhaka and Rajshahi districts in boro, and in Comilla and Cox’s Bazar districts in aman seasons.|
|1985||Hopperburn in Faridpur and Gazipur districts in boro, and in Sherpur district in aman seasons.|
|1986||Outbreaks in 6 districts in boro, and 6 districts in aman seasons.|
|1989||Localized outbreaks in some parts of the country.|
|1990||Severe outbreak in Manikgonj, Gopalgonj and Faridpur districts in boro season.|
|1993||Localized outbreak in Rajshahi district.|
|1997||Outbreaks in 4 districts in aman season.|
|1998||Hopperburn in several districts.|
The white-backed planthopper (WBPH) had been considered as a pest from 1981 and the first significant hopperburn caused by this pest was recorded in Chittagong district in 1985. Occupying very similar ecological niches, the WBPH and BPH were often present in the same field, and they have similar patterns of abundance with two distinct peaks coinciding with the reproductive phase of boro and aman rice crops (Fig. 1).
WBPH had usually been less abundant and less damaging than BPH. The recent outbreaks occurred at a time when scientists and agriculture extension officials started to believe that the populations of the both planthoppers have declined. In Bangladesh hybrid rice was introduced at the end of 1990s, adoption of which was intensified in recent years. In the 2009 boro season mass media (national TV channels and news papers) reported planthopper outbreaks in 13 out of 64 districts. The Plant Protection Wing of the Department of Agriculture Extension reported 2500 ha planthopper affected area out of 4.5 million ha of boro rice. Entomologists of the Bangladesh Rice Research Institute (BRRI) visited the affected areas in four districts and verified that the outbreak was mainly due to WBPH, and observed that some fields were infested solely by millions of WBPH.
BRRI entomologists also observed that in addition to planthoppers blast disease especially neck blast was a major problem in the planthopper outbreak areas. Blast damage in some fields was as high as 50-100%. The most popular boro variety, BRRI Dhan29, was severely affected by blast. The observation indicates a suspicion that the outbreaks of planthoppers and blast disease may be related with overuse of nitrogenous fertilizer and hybrid rice cultivation intensification. Because of low price of locally produced nitrogen fertilizer farmers tend to overuse N-fertilizer. Excessive use of N-fertilizer positively influences populations of both the planthoppers and blast pathogens.