SYMPTOMS
Lower leaves develop small, ¼-to ½-inch (6 to 13 mm) pale ocher or light brown spots. Tiny, black fungal fruiting bodies appear inside spots. Spots grow larger and may have yellow halos. The tissue inside spots darkens and dries up. Spots may be rounded or angular (confined by leaf veins).
DIAGNOSIS
leaf spot, canker, and fungus: brown leaf spot (Neodidymelliopsis cannabis, Ascochyta arcuata), yellow leaf spot (Septoria cannabis,
S. neocannabina), Cladosporium stem canker (Cladosporium herbarium), Chaetomium fungus (Chaetomium succedaneum)
SOLUTIONS
• Sanitize
• Weed
• Mulch
• Use baking soda spray
• Use copper
• Plant polycultures
• Choose genetically resistant plants
• Rotate crops
• Create healthy soil
• Decrease nitrogen
• Keep foliage dry
SYMPTOMS
Pale green or gray leaf spots develop into irregularly shaped circles and coalesce. Spots drop out, leaving ragged holes. Leaves turn brown.
DIAGNOSIS
brown blight (Alternaria alternate, A. solani, A. longipes, A. chianti)
SOLUTIONS
• Weed
• Mulch
• Use beneficial fungi
• Use beneficial bacteria
• Use baking soda spray
• Use copper
• Plant polycultures
• Choose genetically resistant plants
• Rotate crops
• Create healthy soil
• Decrease nitrogen
• Keep foliage dry
SYMPTOMS
Sunken, light green, water-soaked spots develop gray-white centers with brown-black borders. Leaves wrinkle and wilt.
DIAGNOSIS
anthracnose (Colletotrichum coccodes, C. demotion)
SOLUTIONS
• Sanitize
• Weed
• Mulch
• Use beneficial fungi
• Use baking soda spray
• Use copper
• Plant polycultures
• Choose genetically resistant plants
• Rotate crops
• Create healthy soil
• Decrease nitrogen
• Keep foliage dry
SYMPTOMS
Whitish powder coats leaves, merging into large spots that easily rub off. Leaves may look sprinkled with flour. Small black specks may form in powder. Infected leaves may become distorted, turn yellow, and then brown.
DIAGNOSIS
powdery mildew (Sphaerotheca macularis, Leveillula taurica)
SOLUTIONS
• Sanitize
• Weed
• Mulch
• Filter the air
• Move the air
• Use beneficial fungi
• Use beneficial bacteria
• Use baking soda spray
• Use neem
• Use horticultural oil
• Use copper
• Use sulfur
• Plant polycultures
• Choose genetically resistant plants
• Rotate crops
• Create healthy soil
• Decrease nitrogen
• Keep foliage dry
• Manage humidity
SYMPTOMS
Yellow spots appear on upper leaf surfaces. Orange or yellow bumps appear on the undersides of leaves, directly opposite yellow spots. Orange or yellow dust (fungal spores) rubs off your fingers.
DIAGNOSIS
rust fungi (Aecidium cannabis, Uredo kriegeriana)
SOLUTIONS
• Sanitize
• Weed
• Mulch
• Filter the air
• Move the air
• Use sulfur
• Plant polycultures
• Choose genetically resistant plants
• Rotate crops
• Create healthy soil
• Keep foliage dry
SYMPTOMS
Spots of white fuzzy mold cover leaves and flower buds. Fuzz turns dusty pink when it begins to make spores under humid conditions. This fungus may girdle stems, causing plants to wilt and topple.
DIAGNOSIS
pink rot (Trichothecium roseum)
SOLUTIONS
• Sanitize
• Weed
• Mulch
• Filter the air
• Move the air
• Plant polycultures
• Choose genetically resistant plants
• Rotate crops
• Create healthy soil
• Decrease nitrogen
• Keep foliage dry
SYMPTOMS
Leaves develop brown spots with no signs or symptoms of pests or diseases. Leaves may turn yellow, and plants are stunted.
DIAGNOSIS
pesticide damage: phytotoxic reactions
SOLUTIONS
• Stop using pesticides
• Wash pesticide residue off plants
SYMPTOMS
Leaves skeletonized (soft tissue eaten away, leaving veins). Leaves may be rolled into tubes and sewn together with silk. A caterpillar hides inside the tube. Look for tiny, black pellets of caterpillar poop.
DIAGNOSIS
leaf-eating caterpillars and budworms: cotton bollworm (Helicoverpa armigera), corn earworm (Helicoverpa zea), flax noctuid (Heliothis fireplace), hemp bagworm (Psyche cannabinella), silver Y moth (Autographa gamma), dot moth (Melanchra persicaria), cabbage moth (Mamestra brassicae), garden tiger moth (Arctia caja), common hairy caterpillar (Spilosoma obliqua), beet webworm (Loxostege sticticalis), hemp dagger moth (Plataplecta consanguine)
SOLUTIONS
• Weed
• Use screens on doors, vents, and windows
• Use cutworm collars
• Turn off lights at night
• Remove pests by hand
• Use beneficial insects
• Use beneficial nematodes
• Use beneficial bacteria
• Use beneficial protozoa
• Use insecticidal viruses
• Use hot-pepper spray
• Use garlic spray
• Use insecticidal soap
• Use neem
• Use spinosad
• Use pyrethrin
• Do not plant near corn (maize)
• Rotate crops
SYMPTOMS
Pale green or silvery white serpentine trails appear on leaves. These are tunnels inside the leaf made by fly larvae (maggots). Trails sometimes coalesce into large blotches.
DIAGNOSIS
leaf miners: agromyzids (Liriomyza strigata, L. euphoria, L. cannabis, Phytomyza horticola, Agromyza reptans)
SOLUTIONS
• Sanitize
• Use row covers
• Use traps
• Use beneficial insects
• Use neem
• Use horticultural oil
• Use spinosad
• Rotate crops
SYMPTOMS
Leaf edges and tips turn brown. You see no signs or symptoms of pests or diseases. Brown leaf tissue stays brown even when the plant recovers.
DIAGNOSIS
leaf scorch
SOLUTIONS
• Create healthy soil
• Manage essential nutrients
• Manage water quantity and frequency