Teaching Healthy Cultivation
Plant Health, IPM & Disease Library
Diagnose from evidence, not a symptom chart. These references start with what can be observed, show important look-alikes, and identify what should be measured or confirmed before choosing a response.
Reference group
Foundations
Build observation, sampling, beneficial-organism, scouting, and sanitation habits that make later diagnoses more reliable.
Foundations
Diagnostic Foundations
A repeatable observation-first workflow for separating environmental, root-zone, nutritional, pest, pathogen, and physical causes before choosing a response.
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Abiotic vs Biotic Damage
Environmental and root-zone disorders can mimic pest and disease symptoms. Distribution, timing, progression, and direct evidence help distinguish them.
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Scouting and Sampling
Good diagnostics depend on representative observations. A repeatable scouting route, consistent sample locations, magnification, and records are more useful than occasional symptom photos.
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Sanitation and Quarantine
Exclusion and workflow design are often more reliable than trying to eradicate a problem after it spreads. Quarantine, clean-to-dirty movement, and validated tool sanitation reduce transmission opportunities.
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Beneficial Arthropods & Biological Control
Predators and parasitoids can be valuable IPM tools, but success depends on matching the beneficial organism to the pest and life stage, releasing it under suitable conditions, and verifying performance through scouting.
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Abiotic disorders
Separate irrigation, root oxygen, salinity, pH, light, temperature, and chemical injury from pests, pathogens, and nutrient look-alikes.
Abiotic disorders
Root-Zone Hypoxia & Waterlogging
Roots require oxygen for respiration and normal water and nutrient uptake. When pore spaces remain water-filled or poorly aerated, root function can decline even though the root zone contains abundant water.
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Drought & Root-Zone Water Deficit
Water deficit occurs when root water supply cannot keep pace with plant demand. The useful diagnostic question is not simply whether leaves are drooping, but whether the root zone is actually too dry or unable to deliver water fast enough.
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High EC & Salt Stress
Excess dissolved salts increase the osmotic difficulty of water uptake and can accompany tip burn, marginal necrosis, slowed growth, or root injury. Symptoms are not specific, so electrical conductivity should be measured rather than inferred from leaf appearance.
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Root-Zone pH Drift & Nutrient Availability
Root-zone pH changes nutrient solubility and availability, but a pH reading does not identify a deficiency by itself. Diagnosis requires a consistent sampling method plus root condition, EC, feed composition, and symptom location.
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Heat Stress & Canopy Overheating
Heat injury is best evaluated at the tissue and canopy level. Leaf temperature can differ from room air temperature, and the most exposed leaves may experience a different combination of radiant load, humidity, and airflow than sensors elsewhere in the room.
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Cold & Chilling Stress
Low tissue or root-zone temperatures can slow metabolism, water uptake, and growth. Chilling symptoms overlap with nutrient and root problems, so temperature history and location matter more than leaf color alone.
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Excessive Light & Photoinhibition
High photon exposure can exceed the capacity of photosynthetic processes, especially when combined with heat, water limitation, or abrupt increases in light. Bleaching and upper-canopy injury should be mapped against measured light rather than diagnosed from appearance alone.
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Edema & Intumescence
Edema and related intumescence disorders are non-infectious tissue abnormalities that can produce blisters, bumps, or corky areas. They are associated with an imbalance between water uptake and water loss in susceptible plants and can be confused with pests or disease.
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Phytotoxicity & Spray Injury
Phytotoxicity is plant tissue injury caused by chemical exposure. Droplet patterns, exposure history, affected tissue age, temperature, light, formulation, concentration, and tank contamination can help separate spray injury from pests, pathogens, and nutritional disorders.
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Herbicide Drift & Growth-Regulator Injury
Off-target herbicide exposure can produce distorted, narrowed, cupped, twisted, stunted, bleached, or necrotic growth depending on the active ingredient and exposure. New growth may be especially informative, but visual symptoms alone cannot identify a specific herbicide.
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Arthropod pests
Identify the organism and life stage instead of treating leaf damage as a diagnosis by itself.
Arthropod pests
Two-Spotted Spider Mite
A common mite pest that feeds by piercing plant cells. Early infestations may appear as fine stippling; webbing is usually a later, heavier-infestation sign rather than a requirement for diagnosis.
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Thrips
Small, slender insects whose feeding can leave silvery or pale scars, distorted tissue, and dark fecal specks. Species and life cycles vary, so identification should be based on the organism as well as damage.
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Fungus Gnats
Small flies associated with moist organic substrates. Adults are primarily a monitoring nuisance; larvae inhabit the root zone and can feed on fungi, organic matter, and tender roots, with the greatest concern in seedlings and stressed plants.
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Aphids
Sap-feeding insects that often cluster on tender growth and leaf undersides. Honeydew, cast skins, and colonies are stronger evidence than leaf curl alone.
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Broad and Russet Mites
Extremely small mites that can produce severe distortion, bronzing, shortened internodes, and abnormal new growth. Symptoms are not specific enough for a visual-only diagnosis.
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Whiteflies
Whiteflies are small sap-feeding insects whose eggs and immature stages occur primarily on leaf undersides. Adults may disperse when foliage is disturbed, while immature stages can be overlooked without deliberate inspection.
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Root Aphids
Root-feeding aphids can be difficult to detect because much of the population lives below the canopy. Declining vigor alone is not diagnostic; confirmation requires root-zone inspection and identification of the organism.
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Mealybugs & Scale Insects
Mealybugs and scale insects can hide at nodes, petioles, stems, and protected crevices. Their waxy coverings and low mobility in some life stages make deliberate close inspection important.
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Leafhoppers & Other Mobile Sap Feeders
Mobile sap-feeding insects can create stippling, chlorosis, distortion, or localized feeding marks, but damage pattern alone rarely identifies the insect responsible.
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Caterpillars & Chewing Insects
Chewing insects remove tissue rather than extracting sap. Holes, missing leaf margins, frass, webbing, and direct sightings are stronger evidence than general discoloration.
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Shore Flies
Shore flies are small dark flies associated with algae and persistently wet greenhouse surfaces. Adults are primarily a monitoring and sanitation signal rather than a direct plant-feeding pest, so they should be distinguished from fungus gnats before management decisions are made.
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Diseases
Separate pathogen evidence from environmental and root-zone conditions that can create similar symptoms.
Diseases
Powdery Mildew
A group of obligate fungal pathogens that produce superficial white growth on susceptible tissues. Early colonies can be small and easy to confuse with residues, so confirmation matters.
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Botrytis / Gray Mold
Botrytis cinerea can colonize senescent or injured tissues and cause destructive flower rot under favorable conditions. Internal flower damage can be advanced before surface sporulation is obvious.
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Damping-Off Complex
A seedling disease syndrome caused by several soilborne fungi and oomycetes. It can occur before emergence or after emergence when the stem or root tissues are attacked.
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Root Disease Complex
Root decline can involve oomycetes, fungi, low oxygen, temperature stress, salinity, chronic saturation, or combinations of these factors. Brown roots alone do not identify a pathogen.
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Fusarium-Associated Wilt & Crown Disease
Fusarium species can be associated with root, crown, and vascular disease, but wilt and vascular discoloration are not specific enough for diagnosis by appearance alone.
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Pythium-Associated Root Rot
Pythium-associated root disease is favored by vulnerable roots and water-mediated spread in many production systems. Brown roots or wilt alone are not enough to establish the cause.
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Leaf Spot Disease Complexes
Leaf spots and lesions can be produced by fungal, bacterial, environmental, chemical, and physical causes. Pattern, progression, environmental context, and laboratory evidence are often needed to separate them.
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Bacterial Disease Concepts
Bacterial plant diseases can produce water-soaked lesions, blights, rots, or vascular symptoms depending on the organism and tissue involved, but those signs overlap with fungal disease and abiotic injury.
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Post-Harvest Mold & Microbial Risk
Harvested flowers remain biologically active and can support microbial growth when moisture availability, temperature, contaminated material, and handling conditions align. Visible mold is a rejection signal, not a quality defect to blend away.
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Root-Knot Nematodes
Root-knot nematodes (Meloidogyne spp.) are plant-parasitic roundworms that can reproduce on Cannabis sativa. Hemp studies show that susceptibility and visible galling can vary, so root symptoms should be paired with soil or root testing before the cause is assigned.
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Septoria Leaf Spot
Septoria species are documented causes of leaf spot disease on Cannabis sativa. Because foliar lesions overlap with spray injury, nutrient-related necrosis, and other pathogens, lesion appearance should be treated as a starting point for diagnosis rather than a species identification.
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Neofusicoccum Dieback & Stem Canker
Neofusicoccum parvum has been confirmed as a pathogen of Cannabis sativa and can be associated with stem lesions and terminal dieback. Dieback is not specific to this fungus, so diagnosis should combine stem inspection, crop history, and laboratory confirmation.
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Sclerotinia White Mold
Sclerotinia-associated white mold has been reported in hemp and cannabis production contexts. White fungal growth and hardened survival structures can be important clues, but laboratory confirmation is appropriate when the diagnosis affects crop-removal or site-management decisions.
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Southern Blight
Southern blight, historically reported under the pathogen name Sclerotium rolfsii, has been reported on hemp and is favored by warm conditions. Crown collapse and surface fungal growth can resemble other root and stem diseases, so the pathogen should be confirmed when possible.
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Systemic pathogens
Use testing and propagation records when visual symptoms cannot establish infection.
Systemic pathogens
Hop Latent Viroid (HLVd)
Hop latent viroid is an infectious RNA agent documented in cannabis. Symptoms can include reduced vigor and yield, but plants may also be asymptomatic; visual inspection cannot confirm infection.
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Virus Disease & Vector Concepts
Plant viruses can cause mottling, distortion, stunting, or no obvious symptoms. Diagnosis requires testing because similar patterns can come from nutrition, herbicide or spray injury, mites, temperature stress, or genetic variation.
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