Date of Award


Degree Name

Master of Science


Plant Biology

First Advisor

Gage, Karla


Renewed interest in hemp (Cannabis sativa L.) for cannabinoid production has highlighted critical knowledge gaps for growers. The impacts of weed interference on hemp yield are largely unstudied despite causing serious economic losses in most cropping systems. Furthermore, understanding factors determining cannabinoid content of hemp will be crucial for effective production. To evaluate the effects of weed competition on hemp yield and cannabinoid content, hemp growing in plasticulture was subjected to competition from 5, 3, 1, or 0 waterhemp (Amaranthus tuberculatus (Moq.) Sauer) plants. Hemp biomass and cannabinoid content were not significantly affected by weed competition. Yields in weedy and weed-free treatments were generally comparable, although unexpectedly high variation limited the ability to detect subtle differences between treatments. Waterhemp biomass was significantly reduced by competition from hemp in comparison to hemp-free controls. Suppression of weed growth by hemp and lack of significant yield loss from weeds suggests that hemp can be highly competitive and grown successfully without herbicides in certain circumstances. Abundance and documented phytotoxicity of hemp secondary metabolites suggest a potential for allelopathic activity. While incorporated hemp residue was not more effective than a maize control at reducing plant growth, hemp residue and extracts effectively inhibit seed germination. A laboratory assay showed that crude extracts of hemp can reduce the germination of a Brassica napus L., a bioindicator. Furthermore, a greenhouse experiment showed that small amounts of hemp residue on the soil surface can effectively reduce and delay the germination of waterhemp. Together, these results show that hemp residue has the potential to be incorporated with a practice such as chaff-lining for enhanced control of germinating weed seeds.

Available for download on Sunday, April 07, 2024




This thesis is only available for download to the SIUC community. Current SIUC affiliates may also access this paper off campus by searching Dissertations & Theses @ Southern Illinois University Carbondale from ProQuest. Others should contact the interlibrary loan department of your local library or contact ProQuest's Dissertation Express service.