Assessing the invasion risk of industrial hemp

Background/Question/Methods

The cultivation of industrial hemp, Cannabis sativa L., has received increasing attention in the United States, and interest is expected to rise following the 2018 Farm Bill legalising cultivation. Since the early 21^stcentury hemp production has been controlled under drug enforcement laws because other varieties of C. sativa (i.e., “marijuana”) have high levels of ∆9-tetrahydrocannabinol (THC), which causes inebriation. By definition, “hemp” has THC levels of < 0.3%, while marijuana has THC levels of > 0.3%. Hemp has been cultivated for fibre, grain, and pharmaceuticals, such as cannabidiol (CBD). Some states already have licensed programs for hemp cultivation, and it’s anticipated that the change in federal status will result in widespread plantings. Although hemp has highly anticipated value as an agricultural commodity, it is known to escape cultivation and may present an invasion risk. In 2018, the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) initiated a pilot project to evaluate hemp cropping systems and to assess invasion risk. Using the Predictive Tool (PT) from the UF/IFAS Assessment of Non-native Plants in Florida’s Natural Areas, we conducted a risk assessment to evaluate the invasion risk of hemp in the U.S and to identify traits requiring further evaluation.

Results/Conclusions

Our results from the risk assessment indicate that C. sativa as a parent species (i.e., generally across hemp and marijuana varieties) scored “high risk” for invasion. In total, the species received 19 points for the 49-question assessment (score of ≥7 is high risk). The questions related to the history of invasiveness elsewhere contributed most to the high invasion risk conclusion. Sufficient evidence supported positive responses to questions 3.01 “Naturalized beyond native range” (+1 point), 3.02 “Garden, amenity, disturbance weed” (+2), and 3.04 “Environmental weed” (+4). Additionally, questions that assess life history traits identified reproductive attributes such as the ability to produce viable seed, hybridize naturally, and self-pollinate as other factors contributing to the high-risk conclusion. Finally, the risk assessment identified gaps in knowledge where additional information or data is needed, such as seed dispersal methods (e.g. animal, accidental, and produce contaminant) and whether hemp can be easily managed with herbicides. Additional research is needed to determine if invasion risk varies among hemp cultivars that will be grown for different purposes (e.g., fiber, grain, CBD) and to develop best management practices for commercial cultivation.