C ISSE W. S PRAGINS , Rockwell Laboratories Ltd., Minneapolis, MN, USA
odents exist closely with man, with rodent populations tending to increase as human populations increase. As man artiﬁcially creates concentrated sources of food, water and harbourage, for his own survival, he often inadvertently creates the ideal environmentfor rodents to thrive. Various control strategies are discussed in terms of integrated pest management (IPM) schemes. These include the use of preventative methods during storage and in-crop as well as the use of various poisons/rodenticides.
Rodent pests signiﬁcantly damage crops before and after harvest with an estimated 20% of the world’s food supply consumed or contaminatedeach year. The most severe in-crop problems occur in tropical plantation crops such as sugar cane (Figure 1), oil palm, cocoa and coconut and also in rice, other cereals and other food crops. While the tropical climates allow many rodent species to ﬂourish, virtually all climates are plagued by the ubiquitous commensal rodent species (Rattus norvegicus (Figure 2) and Mus musculus) which attack grainand other food and feed whilst in storage (Figures 3 & 4, Table 1). Surveys of the degree of rodent crop damage have been conducted and indicate substantial levels in many regions. Examples for certain crops and regions and the primary species responsible are shown in Table 2. entryways should be sealed up, as rodents can enter holes as small as 6mm. Holes should be sealed with hardware cloth,perforated metal, galvanised sheet metal or cement mortar. In indoor storage areas, particularly where the outer building has not been proofed, stored goods should be kept on pallets or in rodent-proof sealed containers. Any spillage around the outside of the store should be cleaned up regularly, as this will attract
Figure 1 (above) Sugar cane damaged by rodents. Photo courtesy of BellLaboratories, Inc Figure 2 (below) Rattus norvegicus with young. Photo courtesy of Bell Laboratories, Inc
IPM CONTROL STRATEGIES
The most effective, economical and environmentally sound control strategies involve the use of integrated pest management (IPM). To protect crops whilst in storage from rodent damage, a few preventative measures will go a long way towards controlling infestations and preventingthem from becoming established in the ﬁrst place. The principal measures include food source removal and harbourage reduction. If possible, crops should be stored in containment which has been rodentproofed. Doors, windows and screens should be tight-ﬁtting and any holes in the structure should be sealed (Figure 5). Rodents can easily enter any hole in a structure one metre below or above groundlevel. All potential
S U S TA I N A B L E D E V E L O P M E N T S I N T E R N AT I O N A L
Figure 3 Wheat store covered with rat tracks and tail drag marks. Photo courtesy of Bell Laboratories, Inc
Figure 4 Rattus rattus. Photo courtesy of Bell Laboratories, Inc
rodents. Outside debris and clutter which provide potential harbourage should be eliminated. Weeds and dense orhigh-standing vegetation should be eliminated for 3-10 m around the outside of stores, and any tree branches which overhang stores should be pruned back (Figure 6). Standing water may also attract rodents and should be eliminated around stores if possible. For controlling rodent pests in-crop, prevention is more difﬁcult, as in most cases large areas are involved and exclusion is not practical (Figure7). Several nonchemical deterrent measures are available, however, and may be used effectively in certain crops and regions. As much as is practical, measures may be taken to reduce harbourage areas in and around ﬁelds by eliminating unnecessary vegetation, garbage, piles of junk, etc. Other measures include burning ﬁelds after harvest to kill or
displace rodent pests, a practice used...