THE AUTHORS 



RESEARCH SUMMARY 



PETER M. RICE is Research Associate, Division of 

 Biological Sciences, University of Montana, Missoula. 



DONALD J. BEDUNAH is Professor of Range Man- 

 agement and Wildlife, School of Forestry, University 

 of Montana, Missoula. 



CLINTON E. CARLSON is Research Scientist, 

 Intermountain Research Station, Forestry Sciences 

 Laboratory, Missoula, MT. 



ACKNOWLEDGMENTS 



This cooperative study, INT-90488-COA, between 

 the University of Montana and the Intermountain 

 Research Station is supported by funding from the 

 National Agricultural Pesticide Impact Assessment 

 Program as NAPIAP project numbers INT-12 and 

 INT-17. Herbicides were supplied by Dow Chemical. 

 Tordon, Stinger, Transline, and Curtail are trademarks 

 of DowElanco. Spray applications were made by 

 Celestine Lacey, Weed Management Consulting 

 Service, Helena, MT. Residue analyses were con- 

 ducted by Russell Leu at Montana State University 

 Pesticide Laboratory under the direction of Laszio 

 Torma. 



Herbicides were applied to replicated treatment plots 

 at four sites in west-central Montana with light to 

 moderate spotted knapweed (Centaurea maculosa 

 Lam.) infestations. Plant community diversity was 

 determined for two seasons before the herbicide 

 treatments; diversity measurements have been com- 

 pleted for 2 years after the year of spraying. Although 

 knapweed suppression was high, the communities 

 were not converted to grass monocultures. Herbicide- 

 caused depressions in community diversity measure- 

 ments were small and transitory. Tordon-treated and 

 Curtail-treated plots showed a small 1-year postspray 

 decline. Diversity on those treatments began to in- 

 crease relative to the untreated plots during the second 

 postspray growing season. Stinger had the least effect 

 on diversity. No large declines in diversity were caused 

 by these herbicide treatments, and the small depres- 

 sions were probably transitory. Community response 

 data collected from a limited set of pilot study plots 

 suggested that the herbicide treatments had increased 

 diversity by 3 years postspray. 



Only small amounts of herbicide were leached below 

 25 cm. Herbicide residuals in the soil at the 25- to 50-cm 

 depth increment were generally undetectable and did 

 not exceed 26 parts per billion at 30 days, trace after 

 1 year, and none were detected after 2 years. 



The use of trade or firm names in this publication is for reader information and does not 

 imply endorsement by the U.S. Department of Agriculture of any product or service. 



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