Emergence and persistence of volunteer hemp in southern Florida

Abstract Introductions of new crops can provide alternate market opportunities, but also may pose ecological risks. New crops lack established management, have uncertain performance issues, and may become weedy in their introduced region. The introduction of hemp ( Cannabis sativa L.) into southern Florida poses a unique introduction scenario because of the subtropical climate and no commercial production on record, unlike in other eastern and midwestern U.S. states. We assessed the escape from cultivation for hemp by tracking establishment and reproduction of volunteer plants from the earliest modern hemp planting in Florida. Hemp is a weed across much of the United States matching its historical distribution and has been assessed to be of high invasion risk for Florida because of its biological attributes, history of escape, and colonization in other states and countries. We conducted monitoring of volunteer plants and a seed establishment experiment in southern Florida finding that hemp volunteer plants occurred in pulses over time, with variable and declining germination. Volunteer plants persisted for up to 2 yr and appeared in areas that were disked and mowed according to USDA-approved hemp crop termination procedures. In the seed establishment experiment, we found that hemp established in disturbed soils (∼9% of seeds planted) and that mean plant heights and seed counts were positively related to soil disturbance and nutrient addition. These findings showed that hemp plantings should be monitored for volunteer establishment, and containment plans should be in place to control the establishment of volunteer hemp plants in agricultural fields. Our study further illustrates the need for multiyear monitoring and repeat termination procedures to ensure containment of hemp volunteers. There was limited evidence of volunteer establishment in surrounding areas and on undisturbed land. However, seed containment, equipment cleaning, and the monitoring of nearby fields and seed transportation routes remains warranted.