Farm management practices can reduce mouse abundance and increase yields
A four-year study in the irrigated croplands of southern NSW investigated the effectiveness of a range of farm management practices to control House Mice and minimise the damage they cause to crops. The project was funded by the BRS National Heritage Trust (National Feral Animal Control Program) and concluded in 2002.
The main objectives of the project were to:
- develop best practice recommendations for mouse control for the summer irrigation area of southern NSW;
- establish a relationship between assessment of mouse density and crop damage, and to identify vulnerable crops and/or crop rotations; and
- extend the results and facilitate the transfer of knowledge to end-users.
A large-scale replicated field study was conducted to examine whether recommended farm management practices could reduce mouse abundance and damage to crops. While it was always believed that there was a relationship between cover and food available to mice, mouse abundance, and crop damage, these elements had never been tested in the field.
Farmers, extension staff and scientists met and developed a list of farm management practices to reduce the impact of mice (Table 1). The treatment actions were tailored to different crop types and seasons. In our field experiment, farmers on the treatment farms followed these recommendations, while the farmers on non-treatment farms carried out their normal practices.
Summary table. Importance of farm management practices for mouse control for the irrigated farming systems in Southern New South Wales. These practices were developed with the advisory panel (farmers, extension staff, farmer groups and scientists) and independently reviewed by farmers for their importance for mouse control.
The main difference in activities between treatments was grazing, and spraying weeds and grasses around perimeter of crops. There were other differences specific to crop types.
Mouse abundance was monitored using live-trapping capture-mark-release methods and census cards (a simple index of mouse abundance) every six weeks. Biomass of grasses and weeds was recorded, and damage to crops was assessed just prior to harvest of winter and summer crops.
Key findings
- Mouse numbers fluctuated in an annual pattern, with peak numbers in winter (June/July) and lowest numbers in spring (October/November) each year. Mouse population abundance was generally low to medium throughout the project.
- There were significant reductions in abundance of mice on treatment sites when populations were highest, and there was no difference between treatments when mouse populations were low. Overall, abundance of mice on treated sites was significantly lower than on untreated sites.
- In all cases, biomass was significantly lower on treated sites compared to untreated sites because of the spraying and grazing conducted by the farmers on the treated sites.
- Damage to crops was low (< 5%) at all times throughout the project. Mouse damage on average over the four years: winter cereals 1.7%, soybean 1.0%, rice 0.6%, and maize 5.5%.
- Yields were significantly higher on treated sites compared to untreated sites for winter cereals and rice crops, but not for soybean crops. Increases of yield of up to 40% occurred on treated sites.
- Weak positive relationships were found between damage to crops and abundance of mice for winter cereals and rice.
- Spraying with herbicides to margins of winter cereal crops to reduce weeds and grasses significantly reduced plant growth by 47% and abundance of mice on sprayed sites by up to 77%.
- The results from this project have influenced the management of mouse plagues through:
- uptake of recommendations by NSW government,
- incorporation of best practice recommendations into the baiting permit for bromadiolone,
- inclusion of “best practice” recommendations and monitoring techniques into the wheat CROPCHECK card system,
- up-to-date information included into MOUSER VERSION 1.0 (CD-ROM) an information transfer and decision support system for the management of mice,
- information was provided for inclusion into the “Mouse-Off®” booklet produced by Animal Control Technologies (Pty. Ltd.) for management of mice, and
- input was provided into NSW Agriculture/Rural Lands Protection Board (RLPB) “Mouse survival guide for Rural Lands Protection Board Staff” (a manual distributed to all RLPB staff throughout NSW and used as the basis for management of mice for pest animal control training courses).
A questionnaire was sent to farmers in the region to obtain feedback on the recommended farm management practices. See Table 1 for the actions considered important for mouse control. All the respondents thought that the recommendations were appropriate and that a real test of the practices would occur when mouse densities are high (mouse plague year).
The findings from this project confirm that reducing the amount of cover and food available to mice reduces mouse abundance, resulting in higher yields of summer and winter crops in irrigated systems. Higher mouse abundance is required to further test whether or not the recommended practices will lead to a reduction in observed mouse damage. While these results are derived from complex irrigated systems we believe the results are generally applicable to other grain growing areas.
This project team have written the following peer-reviewed scientific articles:
- Brown, P.R., Davies, M.J., Croft, J.D., and Singleton, G.R. (2003). Impact of farm management practices on house mouse populations and crops in an irrigated farming system. In "Rats, Mice and People: Rodent Biology and Management", (Eds G.R. Singleton, L.A. Hinds, C.J. Krebs and D.M. Spratt), ACIAR, Canberra.
- Brown, P. R., Davies, M. J., Croft, J. D., and Singleton, G. R. (2004). Can farm management practices reduce the impact of house mouse populations on crops in an irrigated farming system? Wildlife Research 31, 597-604.
- Brown, P. R. (2005). The effect of simulated house mouse damage to wheat in Australia. Crop Protection 24, 101-109.
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 CSIRO would like to thank staff from Narrandera Rural Lands Protection Board, New South Wales Agriculture in Wagga, and the Irrigation Research and Extension Committee for their contributions to this project. We also thank the farmers for their generous cooperation and advice.
Estimating rodent numbers - the Census Card
Census cards are 10 x10 cm pieces of normal paper soaked in vegetable oil and pegged to the ground. The oil used is typically canola, and serves as an attractant to mice. The rodent, attracted by the oil, chews the paper. A 1x1 cm grid pattern on each card makes it easy to determine the percentage of each card eaten. Under certain circumstances one whole card (100%) can be eaten in one night. Census cards can be made from a sheet of A4 paper, photocopied and cut up into 6 cards per sheet. Alternatively, a commercial printing company can be used to produce bulk.
Census cards can be used as an alternative to live-trapping as a method of estimating mouse numbers. However, estimations of rodent density calculated from census card percentages are difficult to determine and are less accurate than those derived from capture-mark-recapture (CMR) trapping studies. Census cards are reliable indicators of rodent prevalence. However it is thought this reliability is diminished during periods of high alternate food availability, such as during sowing, crop maturation and grain spillages associated with harvest.
Census cards are set in lines and grids with 10 m between each card (as for CMR trapping). Rigid wire (10-20 cm long) is used to peg the cards into the ground. Fencing wire is ideal. Bending or curling one end of the ‘stake’ will stop the card from being blown up and off the stake, and will make inserting and removing the stakes easier. A 10 litre plastic bucket is ideal for carrying both cards and stakes while setting, checking or picking up cards.
Census cards are checked as early as possible the day after setting. Data are recorded with either a census card datasheet, or a notebook, noting the percentage of each card eaten, along with the date, farm, habitat etc. All chewed cards are replaced with a freshly oiled card. Replacing unchewed cards is not necessary. The oil will function as an attractant for several days.
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