A plant virus is a submicroscopic pathogen made of RNA or DNA in a protein coat, which can only multiply inside living plant cells. Viruses reported on cannabis and hemp include beet curly top virus (spread by leafhoppers), lettuce chlorosis virus (spread by Bemisia whiteflies), alfalfa mosaic virus and cucumber mosaic virus (spread by aphids), among others. Symptoms include mottling, mosaic patterns, leaf curl, yellowing and stunting.
In practice
There is no cure for a virus-infected plant. Management is prevention: clean propagation material, controlling the insect vectors, removing weeds that host viruses, and roguing infected plants early. Diagnosis needs a lab test such as ELISA or PCR, because symptoms overlap heavily with nutrient problems, genetic leaf variegation and viroid infection.
Myth check
Tobacco mosaic virus (TMV) gets blamed for nearly any mottled cannabis leaf, and smokers' hands are often named as the source. TMV can infect cannabis experimentally, but confirmed natural cases on cannabis are rarebeing reviewed. Mottled leaves usually have another cause. Label: Contested. See HLVd and viruses.
Don't confuse with
- Viroid: no protein coat, no genes.
- Genetic variegation: stable in a cut, not spreading.
Hemp is cannabis grown for fibre, seed or other uses and, in many laws, defined as Cannabis sativa with no more than 0.3% THC by dry weight.BCTV, a leafhopper-spread curtovirus that stunts outdoor hemp and cannabis, curling and yellowing new leaves; there is no cure once a plant is infected.Small wedge-shaped jumping insects of the family Cicadellidae that suck plant sap; the beet leafhopper (Circulifer tenellus) spreads beet curly top virus to hemp.Small white-winged sap-sucking insects of the family Aleyrodidae, mainly Trialeurodes vaporariorum and Bemisia tabaci, that fly up when disturbed and coat leaves in honeydew.Small soft-bodied sap-sucking insects of the family Aphididae that cluster on stems and leaf undersides, excrete sticky honeydew and multiply rapidly by live birth.Pest and disease prevention by changing how the crop is grown, such as humidity, airflow, spacing, watering and cultivar choice, so pests and pathogens struggle to establish.The smallest known plant pathogen: a short circular RNA, usually 246-401 nucleotides, with no protein coat and no protein-coding genes, copied by the host's own enzymes.A gene is a stretch of DNA that carries the instructions for one functional product, usually a protein such as an enzyme, and is the basic unit of inheritance.HLVd, a small infectious RNA that spreads through sap and tools, causing stunting, brittle stems, small loose buds and reduced resin in cannabis; called dudding.
