Entomology Division, Bangladesh Rice Research Institute, Gazipur 1701, Bangladesh
R. G. MORTON
ULG Consultants Limited, Birmingham Road, Saltishford, Warwick CV34 4TT, United Kingdom
B. P. JUPP
Department of Biology, College of Science, Sultan Qaboos University, Muscat, Sultanate of Oman
The effects of rat damage on deepwater rice (DWR) yields were evaluated in 1987 and 1988 by the use of exclusion fences in the Bangladesh Rice Research Institute's DWR site at Rajbari, Gazipur. Bandicota indica (Bechstein) and B. bengalensis (Gray and Hardwicke) started cutting the elongating stems from August and continued until harvest (November). Damage to stems and panicles was much higher in 1987 than 1988. Damage at the elongation stage (47%) was higher than at the ripening stage (34%). Estimated yield losses were 68% in 1987 and 32% in 1988 (average 47%). Management of rats is essential in such highly infested DWR areas. A simple and inexpensive rat control method needs to be developed for the subsistence DWR fanners of Bangladesh.
Deepwater rice, Bandicoot rats, Plant damage, Plant compensation, Yield loss
By the use of exclusion fences in the Bangladesh Rice Research Institute's DWR site at Rajbari, Gazipur, Bangladesh
Deep water rice, Rats
Therefore, studies were undertaken to assess actual yield loss in DWR due to rat damage during the whole growth period by using rat exclusion fences.
Experiments were conducted in the Bangladesh Rice Research Institute (BRRI) DWR site at Rajbari, Gazipur during 1987 and 1988. The site is a small DWR area adjacent to a village and an elevated road in the Meghna floodplain. It is considered to have high rat populations. Experiments were conducted to assess yield losses in the fertilized and unfertilized plots by the use of rat exclusion fences. High installation and maintenance cost of fences limited the number of treatments and replications. The experiment in 1987 had three treatments (unfenced: 0 and 60 kg N/ha, and fenced: 60 kg N/ha) with only two replications. A completely randomized block design was used. The unit plot size was 25 m2 (5 x 5 m). Fences were constructed of wire netting fixed to poles at the corners and sides with a 30 cm strip of galvanized sheet at the top to prevent rats getting a foothold (Figure 1). The base of the fence was buried 10 cm in the earth. Fences were made 195 cm high, which was 35-45 cm higher than the maximum flood depths of previous seasons. Six-week-old seedlings of an advanced breeding line, BR224-2B-2-5, were transplanted on 12 June at 20 x 20 cm hill spacing (three or four seedlings/hill). Ten days after transplanting, nitrogen fertilizer as urea supergranules (USG) was applied into the mud at 40 x 40 cm spacing (deep placement). Excessive flooding in 1987 submerged the top of the fences by about 100 cm by the end of August. Despite a plastic extension fitted to the fences, rats gained access to one, causing severe damage.
A similar experiment was conducted in 1988 as a 2 x 2 factorial, and treatments were 0 and 60 kg nitrogen/ha, in fenced and unfenced plots. The trial was arranged in randomized complete block design with three replications. Unit plot size, rice variety, crop establishment and fertilizer application methods were similar to those in 1987 but a higher number of seedlings (five to seven per hill) and closer spacing (15 x 15 cm) were used in 1988. The crop was established on 7 June. Since flooding overtopped the fences in 1987 the height of the fences was increased to 260 cm; but the unprecedented flood in 1988 again overtopped the fences and it was necessary again to extend fence height by plastic sheeting. During the flooding period a few rats gained access to the fenced plots but were eradicated by trapping. In both study years level of rat damage to elongating stems was estimated by using a floating type of quadrate from the side of the boat. At harvest, panicle density and extent of rat damage were estimated by quadrate counts. Whole plots were harvested and grain yields adjusted at 14% moisture content.
INTERNATIONAL JOURNAL OF PEST MANAGEMENT, 1993, 39(2) 250-254
Grain yield in the fenced plots was adjusted for rat damage at the ripening stage. Since nitrogen was ineffective, grain yields in fenced and unfenced plots were grouped irrespective of fertilizer treatments. Ratprotected plots produced about 0-78 t/ha higher grain yield over the uncontrolled plots in 1987, and 0-51 t/ha in 1988. Yield losses were estimated at 68% in 1987 and 32% in 1988. Loss averaged at about 47%, which must have been higher if fences could have been made completely rat-proof. Studies clearly demonstrated that the bandicoot rats may cause severe losses to DWR, particularly in high rat population areas. In high-infested areas such as the Rajbari DWR site, control of rats is essential.
high lands, so populations may be controlled by collective efforts of poison baiting and trapping in the island villages, highway shoulders and other raised lands (Ahmed and Karim, 1984). This approach has to be adapted collectively by groups of farmers, with the attendant risk of poisoning chickens and other domestic animals as they also concentrate in the limited high lands during the flooding period. Organizing group actions is often too difficult, as individuals have different ideas and interests unless institutional assistance in terms of materials (rodenticide and baiting stations) and money is provided. Therefore, an easy method of bandicoot rat control in DWR which can be adapted by the individual farmers is necessary. As DWR is grown by subsistence farmers the method has to be inexpensive. The use of traps in the flooded rice fields is likely to overcome difficulties in group organization and poisoning of domestic animals.