An assessment of chemical control options for whitebrush (Aloysia gratissima) in South Texas

Abstract

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  Whitebrush (Aloysia gratissima) is a native shrub in South Texas that has become a nuisance on rangelands by forming monoculture stands often requiring intensive management. Whitebrush is drought deciduous (i.e., defoliation in response to moisture stress), which limits the traditional window of opportunity for foliar herbicide applications.
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  In 2020, a new herbicide in the picolinic acid family (Invora; aminocyclopyrachlor + triclopyr [ACP + T 1:2]) capable of offering high levels of control for select resprouting woody species was approved for use in rangelands. Our field trials demonstrated Invora provided high levels of control when applied as individual plant (IPT, mortality = 100%) and broadcast (BC, mortality = 98.6%) foliar treatments regardless of season (P = 0.29, α = 0.05) two years after treatment.
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  We also found foliar-like applications of other commonly used herbicides can be highly effective when applied to dormant shrubs (IPT mortality = 99.7%, BC mortality = 83.5%) with at least 2.5% surfactant in the chemical mix.
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  Laboratory testing indicated high variation in the percentage of viable seed produced annually between whitebrush populations (6%–49%), providing insight into population recruitment strategies post-treatment.