Plant Problem Diagnosis Key

How the key works

Each question splits the possibilities into a few groups by something visible on the plant: where the damage started, what it looks like, what is on the roots. Each answer leads to the next question until one problem is left. Answered questions stay on the page above the open one, and choosing one reopens it to try a different branch.

What it covers

• Pests: mites, thrips, aphids, whiteflies, gnats, beetles, caterpillars, slugs, scale, mealybugs and root-knot nematodes; on trees, emerald ash borer, bark beetles and other borers, sapsuckers, tent caterpillars, bagworms, spongy moth, galls, hemlock woolly adelgid, pine sawflies, spotted lanternfly, lace bugs, elm leaf beetle and cicada or twig girdler damage.
• Diseases: mildews, rusts, gray mold, leaf spots and blights, wilts, root rots, viruses and damping-off; on trees, fire blight, Dutch elm disease, oak wilt, cankers, wetwood, root and butt rot, needle cast, anthracnose, tar spot, cedar-apple rust, black knot, crown gall, bleeding canker, white pine blister rust, bacterial leaf scorch, elm yellows and boxwood blight.
• Nutrients: nitrogen, phosphorus, potassium, magnesium, calcium, sulfur, iron, manganese, zinc and boron, plus excess feed and pH lockout.
• Growing conditions: water, heat, cold, light, herbicide injury and fruit disorders; on trees, girdling roots, trunk wounds, winter sunscald, winter burn, road salt, construction damage to roots, leaf scorch and normal fall needle drop.

Search by description

The box at the top compares a description with the words growers most often use for each problem and lists the closest three. It reads plurals, common misspellings and "no webbing"-style negatives. A crop, picked or named in the description ("brown tips on my strawberry leaves"), moves up the problems common on that crop and the usual cause of the symptom there. When two matches are close, one question built from the sign that sets each apart helps choose between them. A match is a starting point: "Confirm in the key" fills in the answers that lead to it and opens the last question, where it sits beside the problems most like it.

Matching runs in the browser and is not driven by AI. Nothing typed leaves the device unless you rate the matches; a rating sends the description, the crop and the matches to Bizon, with no account details, so poorly matched descriptions can be found and fixed. The privacy policy has the details.

Every problem in the key

Pests

• Spider mites
• Broad mites and cyclamen mites
• Russet mites
• Thrips
• Whiteflies
• Fungus gnats
• Shore flies
• Aphids
• Root aphids
• Flea beetles
• Cucumber beetles
• Japanese beetles
• Colorado potato beetle
• Squash bugs and stink bugs
• Caterpillars
• Cutworms
• Slugs and snails
• Leafminers
• Squash vine borer
• Mealybugs
• Scale insects
• Root-knot nematodes
• Emerald ash borer
• Bark beetles of pine and spruce
• Wood borers
• Sapsucker damage
• Tent caterpillars and fall webworm
• Bagworms
• Spongy moth (gypsy moth)
• Galls on leaves and twigs
• Hemlock woolly adelgid
• Pine sawflies
• Spotted lanternfly
• Lace bugs
• Elm leaf beetle
• Cicada and twig-cutting damage

Diseases

• Powdery mildew
• Downy mildew
• Rust
• Gray mold (Botrytis)
• Sooty mold
• Early blight and Alternaria leaf spot
• Septoria leaf spot
• Black spot of rose
• Late blight
• Bacterial leaf spot
• Tomato spotted wilt and impatiens necrotic spot viruses
• Anthracnose
• Mosaic viruses
• Root rot (Pythium and Phytophthora)
• Fusarium wilt
• Verticillium wilt
• Bacterial wilt of cucurbits
• White mold (Sclerotinia)
• Damping-off
• Apple scab
• Fire blight
• Dutch elm disease
• Oak wilt
• Canker diseases
• Bacterial wetwood (slime flux)
• Root and butt rot
• Needle cast and tip blight
• Shade tree anthracnose
• Tar spot of maple
• Cedar-apple and related rusts
• Black knot
• Crown gall
• Bleeding canker
• White pine blister rust
• Bacterial leaf scorch
• Elm yellows (phloem necrosis)
• Boxwood blight

Nutrient problems

• Nitrogen deficiency
• Phosphorus deficiency
• Potassium deficiency
• Magnesium deficiency
• Calcium deficiency (and tipburn)
• Sulfur deficiency
• Iron deficiency
• Manganese deficiency
• Zinc deficiency
• Boron deficiency
• Too much nitrogen
• Fertilizer burn (high salts)
• pH out of range (nutrient lockout)

Growing conditions

• Drought stress (underwatering)
• Overwatering (low root oxygen)
• Heat and light stress
• Cold and frost injury
• Light bleaching
• Not enough light (stretching)
• Herbicide injury
• Edema (oedema)
• Sunscald
• Blossom-end rot
• Fruit cracking
• Blossom drop
• Transplant shock
• Girdling roots and a buried root flare
• Mower, trimmer and animal injury
• Southwest injury (winter sunscald and frost cracks)
• Winter burn of evergreens
• Road salt injury
• Leaf scorch and drought stress
• Normal fall needle drop
• Construction and root damage

Photos

Photos come from Wikimedia Commons and Flickr under licenses that allow reuse, and each result credits its photographer and license.

Confirming a diagnosis

The key narrows things down; it does not replace a lab. Each result lists the signs that confirm it and the problems most often mistaken for it. For a disease on a high-value crop, a plant diagnostic lab (most state extension services run one) confirms the cause for a small fee. Nutrient problems are best confirmed with a soil, media or leaf tissue test.

Sources

Each result lists the extension pages behind it. Temperatures, distances, rates and timings come from those pages; a few are marked Bizon estimate where no published number was found. Full list: sources.

Prevention and treatment

On the Home and Pro plans each result adds what brings the problem on, how to prevent it, and treatment options in the order to reach for them: cultural first, then biological, then chemical. Chemical options name active ingredients and their resistance groups rather than brands. Product labels differ by crop, site and state, and the label is the legal word on any product.