Aphid Herbivory on Industrial Hemp, Cannabis sativa L., and the Impact of Plant-Soil Feedbacks on Hemp Performance in Louisiana

Industrial hemp, Cannabis sativa L., is defined as having less than 0.3% delta-9-tetrahydrocannabinol by dry weight. It can be grown for fiber, food, oil, and cannabinoids. As a newly legalized crop, little research exists regarding the cultivation or pest management practices in Louisiana. The versatility of industrial hemp may allow for substantial future production in Louisiana. This project set out to understand the impact of previous crops on hemp performance and soil microbial communities. Soybean, Glycine max L. (Merr), grain sorghum, Sorghum bicolor (L.) Moench, and sweetpotato, Ipomeae batatas (L.) Lam, were selected as soil conditioning crops because they are commonly grown in Louisiana and are often grown in rotation. The results showed that hemp performed best in fallow soil over soybean, sweetpotato, and sorghum. Although hemp grown in soybean underperformed when compared to the fallow treatments, it outperformed hemp in sweetpotato and sorghum soils. Reduced performance by hemp in sweetpotato and sorghum soils is likely a result of the well documented allelopathic effects of these two crops. These results indicate that growing industrial hemp after a fallow period may produce the best yield, but hemp grown in rotation with soybean will outperform rotations with sweetpotato or sorghum. This experiment also set out to quantify the ability of aphid pests, Myzus persicae (Sulzer), Aphis gossypii Glover, and Phorodon cannabis Passerini, to colonize industrial hemp in Louisiana. The rates of population increase seen by M. persicae and A. gossypii indicate that they are unlikely to colonize hemp in Louisiana, but they may pose a threat as virus vectors. The rate of population increase for P. cannabis confirms that these aphids pose a threat for colonization of hemp and may also pose a threat as virus vectors