Integrating the fire-grazing interaction with herbicide treatments: A novel approach to controlling Lespedeza cuneata in the tallgrass prairie

Background/Question/Methods

Sericea lespedeza is a perennial, invasive legume rapidly invading native tallgrass prairie in the central United States.  Sericea quickly establishes and spreads into dense stands through multiple physiological advantages and prolific seed and propagule production.  Traditional prairie maintenance and sericea control efforts are ineffective in singular application: fire promotes germination, grazing pressure ceases beyond early growth due to high tannin content, and herbicides provide only short-term control.  However, we argue through the incorporation of ecologically-based invasive plant management which integrates fire, grazing, and spot-application of herbicide, successful control of sericea is possible.  We sought to determine the factors (i.e. environmental or management practice) most influential on successful sericea control.  We established 21 (2010) and 14 (2011) permanent transects within recently burned patches (within pastures) in the Tallgrass Prairie Preserve of northern Oklahoma.  Within 16 m² quadrats along each transect, we quantified pre-treatment sericea density, percent cover and stems grazed.  Following a seasonal burn and intense grazing, one fourth of each transect was assigned to each of the following spot-spray herbicide treatments: early-season, mid-season, late-season, control.   Using multiple regression, we analyzed changes in sericea density and cover one growing season after treatment (GSAT).

Results/Conclusions

On average, early and mid-season spray-treatments produced the greatest control of sericea, reducing stem density and percent cover by 68% and 83%, and 67% and 72%, respectively.  The late-season spot- spray treatment reduced sericea density by only 21% and cover by 44%.  Stem density and cover within quadrats receiving no treatment significantly increased by 99% and 67%, respectively.  However, we found a significant interaction between spray timing and soil type, in which early and late sprays were significantly less successful than mid-season sprays in 2 of our 5 major soil types.  We found control of sericea to be most successful in pastures maintained with a 2 year Fire Return Interval (FRI).  Sericea control increased significantly with increased effective stocking density (head/acres/patch).  Our preliminary results indicated greatest control may be achieved through maintaining a 2yr FRI fire-grazing regime treated with early-season sprays, though soils and stocking density/patch size should also be considered.