Hemp is a dioecious crop, meaning individual hemp plants are either male or female.
“For cannabinoid production the oil is extracted from unpollinated female plants,” said Shelby Ellison, assistant professor with the University of Wisconsin-Department of Horticulture.
A hemp trial plot was the focus of a recent virtual field day, where female hemp plants were actively flowering.
“It’s a hemp-cultivar trial designed to help us understand what varieties perform well in Wisconsin so we can make recommendations to producers,” she said. “The essential oils are more commonly called ‘CBD,’ cannabidiol, or ‘CBG (cannabigerol).’”
Cannabigerol or CBG is a cannabinoid, meaning it’s one of the many chemicals found in cannabis plants, according to online source Healthline. The most well-known cannabinoids are cannabidiol – CBD – and tetrahydrocannabinol – THC – but there’s recently been more interest in the potential benefits of CBG. CBG is considered to be the precursor to other cannabinoids. That’s because when heated CBG-A, the acidic form of CBG, breaks down to form CBG, CBD, THC and CBC – cannabichromene, another cannabinoid.
Because of limitations due to the COVID virus, Ellison is working with Michigan State University and the Michael Fields Agricultural Institute on the same cultivars of hemp. Traits studied include flowering time, susceptibility to pest and disease pressure, plant height and architecture, and cannabinoid content. Plants are sampled at intervals post-flowering to gauge CBD, THC and CBG content. One of the main goals is to be able to tell farmers when the crop is likely to be “too hot” or has too much in THC.
It was a good growing season this summer at the UW-Arlington Agricultural Research Station.
“Starting about mid-July we saw tremendous growth going into mid-August,” Ellison said. “The plants were growing 6 inches to 1 foot per week.”
A group of seedling transplants planted mid-June averaged 4-feet-6-inches as of Sept. 5. Corn borer and hemp borer were the most common insect pests. Weeds weren’t a problem because of wide row spacing that allowed a tractor-pulled rototiller to do mechanical weeding. A week of rain in August totaled 4 inches at the research farm; it caused an increase in downy mildew. Wind caused lodging and plant breakage.
Cannabinoid-trial result numbers are preliminary. As of the virtual field day, five of the cultivars had been harvested for analysis. The CBD content was about 5 percent for the early-sampled cultivars. But Ellison said most growers are interested in THC numbers.
“After three weeks of flowering we have one sample that is already over the acceptable THC threshold and I imagine as we get to week seven we’ll have quite a few of those,” she said. “What might end up happening is that week five is going to be the sweet spot for harvesting while staying in compliance for THC levels.”
The ratio of CBD to THC is important.
“It’s common knowledge that the best available cultivars have a 30-1 ratio,” she said. “(Having) .3 percent THC and 10 percent CBD is about the best combination of those two compounds you can find.”
Early-flowering varieties that had been tested were between 20 and 30 for that ratio.
“That’s where we’re going to be pushing the envelope trying to break that 30-1 barrier for the CBD-THC ratio,” she said.
Final results from the trial will be available when all 44 cultivars have been harvested and analyzed.
“One other thing that I’m passionate about is controlling our existing feral-hemp population,” Ellison said.
Because Wisconsin producers grew a lot of hemp in the 1930’s and 1940’s, feral populations of “wild” hemp have been thriving for the past 70 years with no human intervention. She said she wanted to know of any feral-hemp populations.
“These plants will help populate the new hemp-seed bank in New York state,” she said. “It’s an important resource that we currently don’t have as researchers and plant breeders.”
The UW-Wisconsin Crop Innovation Center is a biotechnology and genomics facility.
“They’ve actually successfully genetically engineered hemp,” Ellison said.
The center has received a grant to work on improving hemp traits using genetic engineering and gene editing. Additional research projects include a National Hemp Research Needs Survey, Organic Fertility Trials, and a collaboration with Lac Courte Oreilles Ojibwa Community College on a Hemp Companion Cropping Study.
A Hemp Tribal Research Initiative for Michigan, called Hemp TRIM, has as a goal to build research capacity in tribal institutions throughout the country, said James DeDecker, director of the Michigan State University-Upper Peninsula Research and Extension Center. The initiative is a partnership between Bay Mills Community College, Little Traverse Bay Bands of Odawa Indians, Michigan State University-Extension and Lake Superior State University to conduct hemp research and outreach. Broadly stated the objective is to disseminate information on potential opportunities and challenges related to hemp production and utilization by tribal communities and partners in Michigan through participatory discussion sessions. It’s a four-year project beginning with variety trials and evaluation. Early hemp-trial plants have been mulched with black plastic for weed control. Because it’s a new venture the learning process of harvest and post-harvest protocols are being established.
Tribes, like states, need to establish and manage own regulatory processes for hemp. The two tribes Michigan State University is working with may have different policies from the state of Michigan, but they have the sovereignty to do so as long as plans are approved by the U.S. Department of Agriculture.
“It’s an exciting opportunity in terms of agriculture and food sovereignty,” DeDecker said.
Visit horticulture.wisc.edu for more information.
Greg Galbraith, a former dairy farmer who owns woodlot property in eastern Marathon County, Wisconsin, writes about the rapidly changing nature of the agricultural landscape. He has built a lifetime connection to the land and those who farm it.