Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2001
Publication Date: 7/1/2002
Citation: Ralphs, M.H., Gardner, D.R., Graham, D.J., Greathouse, G., Knight, A.P. 2002. Influence of defoliation on locoweed vigor, longevity,and toxicity. Journal of Range Management.
Interpretive Summary: White locoweed is widespread throughout the short-grass prairies and mountain grasslands. It is relatively palatable to livestock and they must graze it for 3-4 weeks before signs of poisoning appear. The objective of this study was to determine if clipping to simulate grazing will reduce the vigor, longevity, and toxicity of white locoweed. Paired plants were marked in New Mexico, Colorado, and Utah, and one of each pair was clipped annually for 4 years. Clipping did not substantially reduce vigor, increase mortality, or affect toxicity. However, most plants died during drought periods in the respective regions. Increasing grazing pressure to force consumption of locoweed will not likely reduce white locoweed populations.
Technical Abstract: White locoweed (Oxytropis sericea) is widespread throughout the short-grass prairies and mountain grasslands and causes chronic poisoning of cattle, sheep and horses. Weed theory suggests grazing of weeds that are not normally grazed may reduce their subsequent vigor and structure and abundance in the plant community. The objective of this study was to determine the effect of clipping on vigor, longevity and toxic alkaloid concentration of white locoweed. One hundred large and small paired locoweed plants were marked in each of New Mexico, Colorado and Utah, and one of each pair was clipped at ground level annually for 4 years. Vigor measurements were taken annually on each plant: number of stalks, number of flowering heads, leaf length, and head height. Mortality was noted and the toxic alkaloid swainsonine was measured. Clipping did not universally reduce vigor. Flowering heads/plant declined in most plants, and stalks/plant declined in large plants in Utah, but clipping did not affect other parameters. Clipping had no effect on longevity or swainsonine concentration. Large plants had a higher rate of mortality than small plants. There were negative correlations between locoweed mortality and precipitation. Most of the marked plants died during the recent years of drought.