Beet curly top virus (BCTV) is a plant virus with a circular, single-stranded DNA genome that can infect various vegetable and ornamental crops, including cannabis. BCTV is spread solely by the beet leafhopper (Circulifer tenellus), a small insect that feeds on the sap of beets and other plants. This feeding behavior can transfer the virus from infected to uninfected plants, allowing it to enter the plant and multiply, causing a range of symptoms that can significantly impact the growth, yield, and quality of the infected crops.
BCTV is characterized by a yellowing of leaves, leading to a yellow-green mosaic pattern. As the disease progresses, it can lead to stunted growth, and twisting of leaves and lateral branches, which is why it's called "beet curly top". These symptoms reduce the size and stature of the plant and can reduce yield, flower quality and cannabinoid content (Galidi et al, 2020).
As an insect-vectored virus, BCTV primarily affects outdoor cultivated cannabis. So far, the detection of BCTV has been limited to outdoor-grown hemp in the mid-western United States (Galidi et al, 2020), and is limited to areas where the beet leafhopper lives. A recent survey of outdoor grown hemp in Colorado showed that BCTV was present in each of the twelve counties tested at rates ranging from 22-100% of plants tested (Chiginsky et al., 2021). This study identified 2 of 11 known BCTV strains in most BCTV-positive cannabis samples, often with both present in the same sample. These are luckily considered to be two of the ‘milder’ strains. It is not clear if strains that cause more severe symptoms are less capable of infecting cannabis, or if they were simply less prevalent in the geographical area of the survey, but as more cannabis is planted in these areas, the more severe BCTV variants will have more opportunity to adapt to infection of cannabis.
To prevent BCTV from spreading in cannabis cultivations, it's essential to implement proper control measures, such as removing and destroying infected plants, and regularly checking for leafhoppers that may carry the virus. One of the most successful measures is the use of biological control methods, such as the release of beneficial insects, including ladybugs and green lacewings, which feed on leafhoppers and other pests. These methods are more sustainable and environmentally friendly than application of commercial pesticides, and they can help to stop the spread of BCTV from crops and weeds in surrounding areas.
In conclusion, in areas where the beet leafhopper is present Beet Curly Top Virus is a serious threat to cannabis cultivations, and can cause significant yield losses, lower bud quality, and potentially lead to plant death. To prevent the spread of BCTV, cannabis cultivators must implement proper pest control measures, including the use of beneficial insects. With the right preventative measures in place, cannabis cultivators can help to ensure the success and profitability of their cultivations.
References
Chiginsky J, Langemeier K, MacWilliams J, Albrecht T, Cranshaw W, Fulladolsa AC, Kapuscinski M, Stenglein M and Nachappa P (2021) First insights into the virus and viroid communities in hemp (Cannabis sativa). Front. Agron., 3:778433.
Giladi Y, Hadad L, Luria N, Cranshaw W, Lachman O and Dombrovsky A (2020) First report of Beet Curly Top Virus infecting Cannabis sativa in Western Colorado. Plant Dis., 104:999.
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