Hemp and Cannabis Diseases
1. Viroid Diseases of Cannabis and Hemp
- HLVd (Hop latent viroid), although latent in hops, this viroid has been reported to cause symptoms of yellowing, malformed leaves, and stunted growth in cannabis.
2. Viral diseases of Cannabis and Hemp
Several significant viruses have been reported to affect hemp:
- Beet curly top virus (BCTV)
- Alfalfa mosaic virus (AMV)
- Arabis mosaic virus (ArMV))
- Cucumber mosaic virus (CMV)
- Lettuce chlorosis virus (LCV)
- Tobacco ringspot virus (TRSV)
- Tomato ringspot virus (ToRSV)
- Tobacco streak virus (TSV)
- Tomato mosaic virus (ToMV)
Symptoms of these viruses on hemp may include mosaic, chlorosis, leaf mottling, and stunting.
3. Phytoplasma Diseases of Hemp
- Candidatus phytoplasma trifolii causes symptoms of leaf curling, mottling, and chlorosis, witches’ broom, stunting and node shortening. This disease has now been detected in Cannabis sativa in USA. AL&L published finding of a phytoplasma (Phytoplasma trifolii) from Cannabis (Plant Disease 3/2019). Find the article here: First Report of ‘Candidatus Phytoplasma trifolii’ Associated with a Witches’ Broom Disease in Cannabis sativa in Nevada, U.S.A.
4. Bacterial Diseases of Hemp
- Bacterial leaf spot caused by Pseudomonas syringae appears as small water-soaked leaf spots that may enlarge along the veins, turning brown.
- Xanthomonas Blightcaused by Xanthomonas campestris pv. cannabis causes leaf spots and wilt.
5. Fungal Diseases of Hemp
Diseases affecting roots and stem
- Fusarium Wilt caused by Fusarium oxysporum f.sp. cannabis. Symptoms of Fusarium wilt disease include yellowing of leaves, poor growth, and wilt. The fungus survives in soil as long lasting chlamydospores. Fusarium wilt can also spread through infected cuttings and airborne spores, or insects such as fungus gnats.
- Fusarium root rot caused by Fusarium solani appears as brown lesions in roots and lower stem.
- Pythium root rot and Damping off Disease is caused by various Pythium species. Symptoms on the mature plants may vary from small roots lesions to severe root damage. Stunted growth and yellowing of leaves may also occur. Damping off disease affects young seedlings.
- Thielaviopsis root rot caused by Thielaviopsis basicola, causes yellowing of leaves and stunted growth.
- Charcoal rot caused by Macrophomina phaseolina appears first as chlorotic leaves followed by rapid wilt and death of the plant. Small black sclerotia are visible on the stalk.
- Botrytis canker and stalk rot (grey mold) caused by Botrytis cinerea. This disease also affects flower buds.
- Hemp canker caused by Sclerotinia sclerotiorum first appears as watersoaked lesions on stalks and branches. These later turn to form cankers. Cottony white mycelium and black sclerotia may also be present.
- Rhizoctonia sore shin and root rot caused by Rhizoctonia solani shows as leaf chlorosis and wilt. Brownish canker develops in the base of the stalk. Black colored flat sclerotia may also be present.
- Phomopsis leaf spot and stem canker caused by several Phomopsis species.
- Verticillium wilt caused by Verticillium dahliae affects several host plants. It can be an issue in soils that have long agricultural history with crops such as cotton, lettuce or tomatoes.
Diseases affecting leaves
- Powdery
mildew, caused by Sphaeorotheca macularis
or Leveillula taurica, is probably
the most common foliar disease of cannabis. White powdery growth appears on the
leaf surface that turns brown later on. Leaves often turn yellow, and brown. - Alternaria
leaf spot and Brown blight caused by several Alternaria species. - Cladosporium, Stemphylium,
Pseudocercospora, Septoria, Phoma, Ascochyta, Colletotrichum, Curvularia, and Leptosphaeria species have all been reported to cause leaf spot
diseases on hemp.
Detection and Diagnosis of Cannabis Diseases
| Pathogen | Assays available at AL&L | Assay type |
| BCTV | yes | qPCR |
| phytoplasma | yes | qPCR |
| HLVd | yes | qPCR |
| AMV | yes | qPCR |
| ArMV | yes | qPCR |
| CMV | yes | qPCR |
| TRSV | yes | qPCR |
| ToRSV | yes | qPCR |
| TSV | yes | qPCR |
| LCV | yes | qPCR |
| Tobamoviruses (ToMV) | yes | qPCR |
| Bacterial diseases | yes | microbial culturing |
| Fungal diseases | yes | microbial culturing |
Diseases of Hops
1. Diseases caused by viruses, viroids and phytoplasmas
- Hop mosaic virus (HpMV) causes chlorotic mosaic and mottling of hops. Infection can lead to severe crop losses.
- Apple mosaic virus (ApMV) symptoms appear as chlorotic rings that turn necrotic. It is a severe virus on hops, and can reduce both yield and quality of the cone crop.
- Hop stunt viroid (HSVd) reduces growth, and can affect yield and quality of the cone crop.
- Hop latent viroid may reduce alpha acid content in some varieties.
- Arabis mosaic virus (ArMV) is a severe, nematode transmitted virus that causes shorted internodes, stunting and shoots that fail to climb.
- Alfalfa mosaic virus (AMV)
- Cucumber mosaic virus (CMV)
- Phytoplasmas can cause severe shoot proliferation and stunted growth.
2. Fungal diseases
2.1 Fungal diseases affecting roots, stem and leaves
- Armillaria root rot caused by Armillaria mellea
- Black root rot caused by Phytophthora citricola
- Downy mildew diseasecaused by Pseudoperonospora humuli
- Fusarium canker caused by Fusarium sambucinum
- Red crown rot caused by Phomopsis tuberivora
- Powdery mildew (Podosphaera macularis)
- White mold (Sclerotinia wilt) caused by Sclerotinia sclerotiorum
- Verticillium wilt caused by Verticillium dahliae and V. albo-atrum
2.2. Fungi causing diseases on cones
Alternaria, Cladosporium, Fusarium, Botrytis, Sooty mold