Hemp and Hop Diseases

Hemp Diseases

1. Viral diseases of 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.

AMV symptoms
AMV symptoms on cannabis leaf

2. Viroid Diseases of 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.

3. Phytoplasma Diseases of Hemp

Phytoplasma symptoms on cannabis leaf.

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.
    Fusarium Canker on cannabis 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