Background/Question/Methods . Medusahead (Taeniatherum caput-medusae) is one of the most problematic rangeland weeds in the western United States.  In previous studies, prescribed burning has been used successfully to control medusahead in some situations, but burning has failed in other circumstances.  In this study, trials were conducted using the same protocol at four locations in central to northern California to evaluate plant community response to two consecutive years of summer burning and to determine the conditions resulting in successful medusahead control.  During 2002-2003 large-scale experiments were established at two warm-winter sites (Fresno and Yolo counties) and two cool-winter sites (Siskiyou and Modoc counties).  Plant species cover was estimated using a point-intercept method, and biomass samples were taken in each plot. 

Results/Conclusions . In the year after the second year burn, medusahead cover was reduced by 99, 96 and 93% for Fresno, Yolo, and Siskiyou counties, respectively, compared to unburned control plots. Other annual grasses were also reduced, but less severely, and broadleaf species increased at all three sites. In contrast, two consecutive years of prescribed burning resulted in a 55% increase in medusahead at the coolest winter site in Modoc County. In the second season after the final burn, medusahead cover remained low in burned plots at Fresno and Yolo counties (1% and 12% of cover in unburned controls, respectively), but at the cool-winter Siskiyou site medusahead recovered to 45% relative to untreated controls.  The success of prescribed burning was closely correlated with the dry biomass of grasses, other than medusahead, preceding a burn treatment.  Forage production was greater in warm-winter areas with a longer growing season.  It is hypothesized that greater production of combustible forage resulted in increased fire intensity and greater seed mortality in exposed inflorescences. These results demonstrate that burning can be an effective control strategy for medusahead in low elevation, warm winter areas characterized by high biomass production, but may not be successful in semi-arid cool winter areas with shorter growing seasons.