Publication Date
1989
Description
In general, inedible weeds of permanent pasture reduce pasture dry matter available to stock in direct proportion to their cover (Doyle et al., 1984). Translating the effects of weeds on pasture to reductions in animal production is difficult because (i) pasture value can range from zero to the cost of purchased feed (ii) weed effects and pasture value can vary seasonally and interact and (iii) reductions in pasture availability at one time affect later growth (Auld et al., 1987). There have been few direct measurements of effects of pasture weeds on animal productivity, because of the co.sts involved. However, simulation models (Barlow, 1985; Popay & Barlow, 1987) allow translation of pasture to animal production for a wide range of conditions and management. Such models, and theoretical analysis of weed and pest effects on grazing (Barlow, 1987), show that the impact of weeds on animal production depends on the level of pasture production, and therefore on stock carrying capacity, and on the nature of the problem. Assuming that there is an on-going, long-term weed problem and the choice is between coexistence with the weed or repeated control to reduce its average cover, then the full benefits of control are only realised by raising stocking rate to utilise the extra pasture production. The models suggest that the percentage gain in per hectare gross margin equals the percentage gain in pasture production through reduced weed cover. If the stocking rate is not raised, the benefits from weed control will be at least 25 % less (Barlow, 1985, 1987; Popay and Barlow, 1987). In addition, using the average of percentage gains in pasture production takes partial account of seasonal variations in the value of pasture (Barlow, 1985). The saving in pasture production made by controlling pasture weeds depends on the reduction in weed cover caused by herbicide application, the recovery rate of weed cover after spraying and the area which the weeds would have occupied during the recovery period if they had not been sprayed. Doyle et al. (1984) and Moore et al. (1988) modelled these processes in detail to explore the cost/benefits for specific weeds. In this paper we bring together this information in summary form for several common pasture weeds and predict the economics of controlling them. Suggestions are made for future research on the biology of pasture weeds which could help in assessing their economic impact.
Citation
Popay, I and Barlow, N, "Economics of Controlling Weeds of Permanent Pasture" (2025). IGC Proceedings (1989-2023). 28.
https://uknowledge.uky.edu/igc/1989/session6/28
Included in
Agricultural Science Commons, Agronomy and Crop Sciences Commons, Plant Biology Commons, Plant Pathology Commons, Soil Science Commons, Weed Science Commons
Economics of Controlling Weeds of Permanent Pasture
In general, inedible weeds of permanent pasture reduce pasture dry matter available to stock in direct proportion to their cover (Doyle et al., 1984). Translating the effects of weeds on pasture to reductions in animal production is difficult because (i) pasture value can range from zero to the cost of purchased feed (ii) weed effects and pasture value can vary seasonally and interact and (iii) reductions in pasture availability at one time affect later growth (Auld et al., 1987). There have been few direct measurements of effects of pasture weeds on animal productivity, because of the co.sts involved. However, simulation models (Barlow, 1985; Popay & Barlow, 1987) allow translation of pasture to animal production for a wide range of conditions and management. Such models, and theoretical analysis of weed and pest effects on grazing (Barlow, 1987), show that the impact of weeds on animal production depends on the level of pasture production, and therefore on stock carrying capacity, and on the nature of the problem. Assuming that there is an on-going, long-term weed problem and the choice is between coexistence with the weed or repeated control to reduce its average cover, then the full benefits of control are only realised by raising stocking rate to utilise the extra pasture production. The models suggest that the percentage gain in per hectare gross margin equals the percentage gain in pasture production through reduced weed cover. If the stocking rate is not raised, the benefits from weed control will be at least 25 % less (Barlow, 1985, 1987; Popay and Barlow, 1987). In addition, using the average of percentage gains in pasture production takes partial account of seasonal variations in the value of pasture (Barlow, 1985). The saving in pasture production made by controlling pasture weeds depends on the reduction in weed cover caused by herbicide application, the recovery rate of weed cover after spraying and the area which the weeds would have occupied during the recovery period if they had not been sprayed. Doyle et al. (1984) and Moore et al. (1988) modelled these processes in detail to explore the cost/benefits for specific weeds. In this paper we bring together this information in summary form for several common pasture weeds and predict the economics of controlling them. Suggestions are made for future research on the biology of pasture weeds which could help in assessing their economic impact.
