The effect of agricultural techniques on the population dynamics and management of Rattus sordidus in sugarcane crops in North Queensland

Rattus sordidus (canefield rat) is a major pest in north Queensland sugarcane growing areas, causing losses of between $2 and $4 million each year. A further $0.2 to $0.4 million is expended on annual baiting campaigns. This procedure provides only short-term results, is seldom cost-effective and is hazardous to non-target species and the environment. There was a close relationship between the dynamics of R. sordidus populations and the crop cycle. During the 1987/88 crop cycle, breeding occurred over the January- July period and coincided with the period when summergrasses were abundant in crops and the predominant food source of R. sordidus. The relationship between the onset of breeding, the first appearance of summergrasses and diet of R. sordidus indicates that breeding is dependent on the availability of a non-cane food source. The level of in-crop weed biomass may therefore play an important role in the regulation of population and damage levels throughout a district. Consequently, a number of agricultural practices which affect in-crop weed levels may have a significant effect on R. sordidus populations. The practice of green cane harvest and trash-blanketing has increased in most northern sugarcane growing districts since the early 1980's. This practice differs to the conventional technique in that crops are not burnt prior to harvest and following harvest the trash, comprising the green "tops" and dry leaf material, is left as a "trash-blanket" on the ground and minimum or zero tillage techniques employed. Suppression of weed germination and growth is a major agronomic advantage associated with this technique. In-crop weed control may also be achieved through the application of herbicides. The monetary benefit associated with yield increases as a result of reduced weed competition in young crops has lead to an increase in the number of crops treated with herbicide. This study investigated the effect of green cane harvesting and trashblanketing, the conventional agricultural practice and herbicide applications on the dynamics of R. sordidus populations during the 1987/88 crop cycle.