Agricultural Experiment StationCooperative Extension Service Publishing Tip of the Month

2012 
SUMMARY Research from 1990 to 2006 investigated prescribed fire and herbicide applications for control of broom snakeweed (Gutierrezia sarothrae (Pursh) Britt. & Rusby) on blue grama (Bouteloua gracilis [Kunth in H.B.K.] Lag. ex Griffiths) rangeland near Corona, New Mexico. From 1990 through 1993 when broom snakeweed populations averaged >2 plants/m², herbicide (picloram) treatments eliminated most broom snakeweed and increased grass yield about 42% relative to untreated areas. Prescribed fires during this period also eliminated most broom snakeweed, but grass yield did not increase relative to untreated areas. Later repeat fires conducted at intervals 6 years intervals generally did not retard grass yield except when drought conditions occurred the first growing season after burning. At the study’s end, burning treatments resulted in higher bareground cover (average interspace area, 23 cm) and less linear grass cover (27%) compared to herbicidetreated and untreated areas (average 16 cm and 36.5%, respectively). This gave the visual appearance of grass cover as being relatively clumpy and less uniform on burned areas compared to a more uniform and continuous grass cover appearance on herbicide-treated and untreated experimental areas. Of the minor grass species studied, only galleta (Pleuraphis jamesii Torrey) seemed to benefit from frequent fire—its linear basal cover nearly doubled relative to untreated areas at the study’s end. Conversely, blue grama linear basal cover was about 9% less on burned areas compared to on nonburned grasslands. Winterfat (Krascheninnikovia lanata (Pursh) A. D. J. Meeuse & Smit) populations were sustained after most single fires, but repeated burns at <5 year intervals reduced this shrub’s abundance and cover. Our study agrees with others that have shown an increase in grass yield following removal of snakeweed with herbicide spraying. However, we did not note a similar beneficial increase in grass yield after burning. Use of prescribed fire on blue grama range in central New Mexico should be viewed as a control alternative for removing broom snakeweed, but not as management practice for increasing forage production.
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