Diseases & Viroids
Fungal, bacterial, viral and viroid problems, disease development, symptom patterns, testing, and risk factors.
Published lessons
These pages are organized here by subject. The permanent THC-ENC IDs remain stable behind the scenes even when a clearer display title is used.
The Disease Triangle and Disease Cycle
Use host susceptibility, pathogen presence, environmental favorability, time, and pathogen life-cycle stages to explain why infectious disease develops and to separate disease risk from symptom appearance alone.
Powdery Mildew Biology
Recognize Cannabis powdery mildew as a living, polycyclic host-pathogen system; distinguish characteristic fungal growth from look-alike residues; and interpret genotype, inoculum, and environment without turning symptom recognition into unsupported treatment advice.
Botrytis Gray Mold and Inflorescence Rot
Identify Botrytis cinerea as a major Cannabis inflorescence-rot pathogen, recognize its disease pattern and epidemiological context, and separate confirmed Botrytis disease from other bud rots and postharvest molds.
Fusarium Root, Crown, and Vascular Diseases
Recognize Fusarium as a diverse group of Cannabis pathogens that can affect roots, crowns, vascular tissues, stems, and inflorescences; distinguish Fusarium syndromes from look-alikes; and interpret propagation, water, and diagnostic evidence without treating genus detection as proof of disease.
Pythium and Oomycete Root Rot
Recognize Pythium-associated damping-off, root rot, and crown rot in Cannabis; distinguish oomycetes from true fungi and abiotic root decline; and use plant, water, and laboratory evidence to support diagnosis without overgeneralizing from one species or production system.
Rhizoctonia and Damping-Off Complexes
Treat damping-off as a seedling disease syndrome with multiple possible biological and abiotic causes; recognize where Rhizoctonia fits in the differential diagnosis; and use root, crown, seedling-pattern, and laboratory evidence before assigning a causal organism.
Sclerotinia and Stem-Rot Risks
Recognize Sclerotinia sclerotiorum white mold and stem/inflorescence rot as a documented Cannabis disease, identify characteristic lesions, white mycelium and sclerotia, and separate this pathogen from other stem and flower rots using tissue and laboratory evidence.
Leaf Spots and Foliar Pathogen Differentiation
Differentiate common Cannabis and hemp leaf-spot syndromes by lesion pattern, pathogen signs, epidemiology, and laboratory evidence, with particular attention to Septoria cannabis and Alternaria species while recognizing bacterial and abiotic look-alikes.
Bacterial Diseases and Opportunistic Infection
Recognize documented bacterial diseases of Cannabis and hemp while distinguishing pathogenic bacteria from commensal, endophytic, epiphytic, saprophytic, and secondary organisms; use lesion pattern, isolation, molecular evidence, and pathogenicity testing to support causation.
Hop Latent Viroid
Understand hop latent viroid as an infectious RNA pathogen of Cannabis, recognize that infection can be asymptomatic or associated with dudding/stunting and quality loss, and interpret tissue testing, propagation, root/water, seed/pollen, and possible insect associations without overstating transmission routes.
Beet Curly Top Virus
Recognize Beet curly top virus as an important hemp virus transmitted by beet leafhoppers, distinguish vector presence from confirmed plant infection, and interpret symptom, strain, seed, genotype, and molecular-test evidence without assuming every curled or stunted plant has BCTV.
Other Viruses and Viroid-Like Symptoms
Interpret mosaic, mottling, chlorosis, curling, twisting, stunting, and other virus-like Cannabis symptoms as diagnostic hypotheses rather than virus diagnoses, and use targeted molecular tests or sequencing to distinguish confirmed viruses, viroids, mixed infections, and noninfectious look-alikes.
Pathogen-Free Appearance Versus Latent Infection
Distinguish visual health from tested pathogen status, understand how latent, asymptomatic, early, localized, or low-titer infections can escape symptom-based scouting, and use risk-based testing without assuming every symptom-free Cannabis plant is infected.
Sampling Plants for Laboratory Diagnosis
Collect representative Cannabis disease samples that preserve diagnostic value, match the suspected pathogen and tissue, include appropriate comparison material and metadata, and support laboratory interpretation without contaminating or biasing the specimen.
False Negatives, Composite Samples, and Test Timing
Interpret negative Cannabis pathogen tests as sample- and time-specific evidence, understand how tissue distribution, pathogen load, assay sensitivity, inhibitors, sampling error, pooling, and infection timing can produce false negatives, and design retesting decisions around biological risk rather than certainty language.
Tool-Mediated and Clone-Mediated Transmission
Trace how pathogens can move with vegetative propagation, infected mother stock, sap-contaminated handling, pruning, and shared equipment while distinguishing demonstrated transmission routes from plausible but unconfirmed contact pathways.
Water, Media, and Facility Reservoirs
Evaluate irrigation water, recirculated nutrient solution, growing media, benches, gutters, emitters, debris, and other facility niches as possible pathogen reservoirs while separating environmental detection from proven plant infection or outbreak source attribution.
Postharvest Microbes and Mycotoxin Context
Interpret postharvest Cannabis microbial contamination, total yeast and mold results, toxigenic fungal detection, and mycotoxin testing as related but distinct quality and safety measurements, and trace contamination across preharvest, harvest, drying, trimming, storage, and analytical stages.
Disease Resistance and Susceptibility
Interpret disease resistance, tolerance, and susceptibility as genotype-by-pathogen-by-environment traits; use replicated Cannabis evidence without converting one resistant accession, locus, or trial into a universal cultivar claim.
Disease Incident Records and Eradication Review
Document a Cannabis disease incident from first signal through diagnosis, containment, source/pathway analysis, corrective action, verification, and closure so conclusions remain traceable and future crop cycles can test whether the problem truly recurred or was resolved.