The quality of cultivars is getting better, according to Cornell’s Jacob Toth. They are seeing less males and less THC in the cannabinoid varieties. Growers learned about the best cultivars at this year’s Hemp Research Team Field Day. Photo by Courtney Llewellyn

by Courtney Llewellyn

By now, many growers know someone growing hemp or have considered looking into the crop themselves. CBD products have proliferated the market and researchers are continuing to find new uses for all parts of the plant. Research continues to be the key in helping to build hemp back up as a legitimate American crop; fortunately, the College of Agriculture of Life Sciences at Cornell University is doing the heavy lifting.

Cornell’s Hemp Research Team hosted a field day at two different sites this summer in Geneva, NY, to speak with growers and potential growers about what’s being accomplished. One site was home to cannabinoid-containing varieties; the other grew cultivars more suited for grain and fiber use. A critical focus at both sites was diversity – testing a wide variety of plants to meet an increasing variety of both grower and consumer demands.

“Why care about conserving hemp diversity?” asked Zachary Stansell, Ph.D., a Plant Genetic Resources Unit geneticist, horticulturalist and curator of the PGRU Hemp Collection with USDA-ARS. The short answer is “to capture and preserve in a safe way all the unique alleles” the plants contain. Stansell’s goal is to conserve, maintain and increase valuable hemp germplasm, as well as ensure these resources are available for research, education and cultivar development. His current research includes understanding the historical, current and future status of hemp germplasm conservation while addressing the numerous bottlenecks within hemp improvement efforts.

“We need a safe harbor that will help us in important ways we can’t even imagine right now,” Stansell noted. “Cannabis is really incredibly genetically diverse. Imagine the value of a breeder being able to look through our list to find the characteristics they want.”

The research prioritizes hemp varieties with low THC for breeders, but Stansell said they want to “cast as wide a net as possible” when it comes to what they’re preserving. For example, they’ve found a variety of hemp that has high powdery mildew resistance – a problem many growers are facing – but it’s still high in THC.

At the Geneva trials, 40 different varieties of hemp were planted on June 10, in what researchers described as good, sandy soil. In addition to evaluating yield and performance, the research team’s aims for the trial included assessing trichome development and cannabinoid accumulation, studying floral morphology and employing remote sensing to understand the relationship between trichome development, floral morphology and cannabinoid accumulation. They grew varieties that produce both CBD and CBG (cannabigerol), which has been called “the mother cannabinoid.” It is another non-psychoactive cannabinoid.

Seeds were provided by Arcadia Biosciences (with a peak of 96% germination), Atlas Seeds (75%), Cornell Hemp (84%), Kayagene (93%), Oregon CBD (99%), Phylos (95%), Phytonyx (100%), Point3 Farma (96%), Davis Farms (100%), Front Range Bioscience (98%) and Alterra Hemp (88%). Clones were also provided by Cornell Hemp, Stem Holdings Agri, Sunrise Genetics, Bazelet Health and Ryes Creek.

George Stack, a graduate student in the School of Integrative Plant Science, noted that 2021 was the fourth year Cornell has done high cannabinoid trials. “The CBG [varieties] have very, very low levels of THC,” he explained. “We also looked at diploid and triploid cultivars, with the triploids reportedly sterile.” Maylin Murdock, a graduate student, said they were rating the more than three dozen varieties for height and flowering time. They used drones and in-field scanners for remote sensing to collect data.

“We want a uniform crop to flower at the same time,” commented Jacob Toth, another Cornell graduate student researching hemp. While this may seem contrary to the idea of diversity, flowering is just one small part of a plant’s genetic makeup. And, he added, “the quality of cultivars is getting better. There are less males, there’s less THC – but we’re still seeing flowering time issues.”

Flowering time is significant because when a plant starts flowering, it stops accumulating biomass, according to Hemp Research Team Project Lead Larry Smart. When flowering starts, “you’ll see lower yield, but you can grow in higher density,” he explained. “The goal is varieties that fit your operation.” He added they also want to develop plants that mature quickly enough for growers to see two harvest cycles in a year.

In addition to figuring out the right varieties for each grower, the researchers are looking at the diversity of diseases that affect hemp. Last year, the team tested six different kinds of biofungicides to thwart the most common issues. The treatments were preventative, not curative.

“We’re mapping one genetic source of resistance [to powdery mildew] with the goal of putting it in everything in the program,” Director of the School of Integrative Plant Science Chris Smart said. Those who tend the fields use a CO2 backpack sprayer using treatments at their label rates, applying weekly applications for six to eight weeks. She added that the team is working on compiling a list of microbials for hemp growers specifically to keep an eye out for.

As for root rot: “There are a number of pathogens that cause root rot, and we focused on fusarium,” said grad student Patrick McMullen. “If you have it, you’ll see low, wilting branches and chlorosis. To identify it, you need to look at plant architecture both above and below ground.” The research team is focusing on multiple management strategies; to fight Bacillus species, for example, they’re applying copper and zinc as drenches. McMullen noted they were seeing good results this summer.

Grain and Fiber Trials

This year is the fifth year of grain and fiber trials in Geneva. Eighteen grain, dual-purpose and fiber hemp cultivars were seeded in replicated small plot trials, with each receiving 75 pounds of nitrogen as pelleted composted chicken manure prior to planting. A cone seeder planted 20 live seeds per square foot for grain and dual-purpose and 40 live seeds per square foot for fiber.

Seeds for these trials were provided by Bazelet Health, Fiacre Seeds, International Hemp, Panda Biotech, Schiavi Seed and UNISeeds Inc. Twelve of the 18 cultivars in the fiber and dual-purpose trials initiated terminal flowering four to five weeks after planting.

Heavy rainfall this July in the region tended to stunt the growth of quite a few plants as well as drown out a number of seedlings. Jamie Crawford, a research support specialist in the School of Integrative Plant Science, noted that hemp is “super susceptible to weed pressure,” and that in addition to a very wet growing season, these cannabinoid-free varieties showed high incidence of herbivory by Japanese beetles.

“Once we obtain our yield, we’ll consider quality,” said Luis Monserrate, graduate research assistant. For now, though, they look at the growth rate, which is measured on a weekly basis. The research team did find that the denser a plot is, the less susceptible plants are to lodging.

Noting which grain and fiber varieties thrive is as critical as finding strong CBD/CBG varieties, as hemp fiber production is finding new uses in construction materials, textiles and animal bedding. Monserrate said they’re even seeing 3-D home printing with hempcrete, a biocomposite material made of a mixture of hemp hurds and lime, sand or pozzolans used for both construction and insulation.

To view the full Hemp Research Team Field Day or to read the research team’s data, check out