Effects of Huisache (Vachellia farnesiana) Control by Herbicide on Understory Forage Elements and Soil Dynamics

Huisache (Vachellia farnesiana) and honey mesquite (Prosopis glandulosa) are both native but invasive woody shrubs. Huisache’s ability to rapidly take over a landscape, and mesquite’s trait of being the first to invade land after a disturbance create a devasting mix that can cause problems for land managers and landowners (Taylor, 2014). From 2022-2024, I studied huisache presence, species composition, forage biomass and nutrition, and soil nutrients at three properties in south Texas that are piloting a novel method of huisache control. In the first year of treatment, they sprayed a reduced rate of less-expensive chemicals (compared to standard recommended treatments) across the whole pasture (24 oz Grazon, 4 oz Tordon, and .4 oz MSM 60). In the second and third years they sprayed the same reduced rate in 60-foot alternating strips. This research aims to investigate the effectiveness of this novel herbicide control method for huisache and understand its effects on forage production, soil composition, and forage nutrition. The results show that treatment resulted in a dramatic decrease in huisache canopy cover and a slight decrease in mesquite canopy cover; forage biomass also increased while total species composition was unaffected. Furthermore, soil nutrients like nitrogen and sulfur increased from the pre-spray periods to the post spray periods, while soil pH levels decreased, becoming more acidic. Finally, the forage nutrition collected during the study was not affected by the treatment. These results can help give landowners and land managers more options when it comes to treatment methods, while also allowing them to consider the risks and benefits.