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Herbicides were applied aerially to honey mesquite (Prosopis glandulosa Torr.) in the Rolling Plains and Edwards Plateau land resource areas of Texas to evaluate efficacy during late season applications. Although other herbicides gave higher levels of above ground mortality, clopyralid caused higher whole plant mortality throughout the growing season than 2,4,5-T + picloram, both of which were ineffective when applied in September. Mixtures of clopyralid + picloram also were less effective when applied during later periods in the growing season, suggestiong picloram added little or even reduced the efficacy of clopyralid for late season control of honey mesquite. Triclopyr alone or in combination with picloram was ineffective in controlling honey mesquite in the fall. Clopyralid in the fall was most effective when applied at rates of 0.56 kg ha-1 or more. Dosage response of honey mesquite in late season applications (late August to October) was practically identical to that found for applications made in June and July, which indicates that clopyralid provides constant levels of mortality throughout the growing season. This research supports the practice of extending the season of applications with clopyralid into the fall. Applications in the fall might allow more rangeland to be treated for honey mesquite reduction and also reduce risks associated with drift damage to crops during their most susceptible periods of growth in early to mid-summer. This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries. The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact lbry-journals@email.arizona.edu for further information. Migrated from OJS platform August 2020