Hot hemp, also known as hemp crops that produce excessive amounts of THC, is a significant concern for hemp farmers. Despite months of meticulous care and expensive practices such as watering, pest control, and soil management, if the THC levels in their crops exceed the federal limit of 0.3 percent, the crops are considered federally illegal cannabis and may be subject to destruction. This worry keeps hemp farmers awake at night, searching for ways to prevent their crops from going “hot.”
While many growers have attributed hot hemp to weather conditions and other environmental factors, recent studies conducted by researchers at Cornell University have revealed that genetic factors play the dominant role in causing the hot hemp phenomenon. Jacob Toth, a graduate student at Cornell University’s College of Agriculture, explained that chemotype-three hemp crops with a CBD:THC ratio of approximately 26:1 are desirable. These plants possess CBDA synthase but lack THCA synthase, enzymes responsible for creating CBD and THC respectively.
Toth’s experiments in 2018 unveiled that the presence of the gene responsible for THCA synthase (referred to as Bt) leads to an overproduction of THC in hemp plants. However, plants with two copies of the gene responsible for CBDA synthase (referred to as Bd) tend to maintain their THC levels within the federal limit. By breeding chemotype-three Bd/Bd plants with only active CBDA synthase genes, farmers can avoid high THC levels.
Avoiding excessive CBD production is another crucial aspect emphasized by Toth. Even chemotype-three crops can breach the 0.3 percent THC limit if they produce too much CBD. Farmers should regularly test their plants’ CBD levels and monitor them closely to ensure they remain below approximately 8 percent.
Alternatively, farmers can choose to cultivate grain- and fiber-type hemp. These industrial crops, often used for products like hemp bags and clothing, tend to have lower THC levels. However, they also have naturally lower CBD levels. These varieties are generally considered safer and less likely to exceed the federal limit.
The experiments conducted by Toth and his team aimed to determine whether environmental factors such as long flowering periods and poor soils were significant contributors to hot hemp. The study conducted in 2019 involved subjecting plants to various stresses such as powdery mildew, damage from a weed whacker, flooding, and exposure to plant growth regulators and herbicides. Surprisingly, while these environmental conditions affected total cannabinoids, the CBD:THC ratio remained consistent across all stressors. This finding further supports the notion that genetic factors are the primary drivers of hot hemp.
Toth acknowledges that there are still some environmental variables left to study, but he remains confident in their genetic hypothesis. Additionally, the Cornell hemp team hopes to validate their findings through gene-editing experiments in the future. These experiments would involve manipulating the presence or absence of THCA and CBDA synthase genes in hemp crops and comparing resulting THC levels.
In conclusion, hemp farmers now have valuable information at their disposal thanks to the research carried out by Toth and his team at Cornell University. By focusing on chemotype-three crops with specific genetic profiles, monitoring CBD levels, or choosing grain- and fiber-type varieties, farmers can ensure compliance with federal regulations for their hemp crops. Although further studies are needed to explore remaining environmental factors and validate genetic theories through gene editing, this research provides a solid foundation for cultivating compliant hemp crops regardless of weather conditions or other external influences.
