Diagnostics
Problems
Pest, disease, and damage diagnostics for outdoor plants. Cited against UC IPM, Missouri Botanical Garden, and Extension diagnostic resources.
Plant diagnostics is the highest-stakes search on a gardening site — you have a sick plant right now. These guides cite the differential diagnosis (e.g., yellow leaves: 8 causes ranked by likelihood, including the boring ones like overwatering), then the treatment hierarchy. Use the diagnose tool to walk through symptoms by question.
Most-viewed in problems
Blossom end rot in tomatoes and peppers: it's not a disease
Blossom end rot is a calcium uptake problem caused by irrigation inconsistency, not a pathogen. Calcium sprays don't fix…
Japanese beetle damage and control: what actually works
Honest comparison of Japanese beetle control methods: milky spore, traps, neem oil, and handpicking. Pheromone traps att…
Powdery mildew on garden plants: identification and treatment
Powdery mildew looks the same on every plant but is caused by different fungal species on each host. Learn identificatio…
How to Get Rid of Aphids Outdoors: What Actually Works
Aphids outdoors are best controlled with water spray and insecticidal soap, not broad-spectrum insecticides. Learn what …
Leaf Scorch: Causes, Identification, and Treatment
Leaf scorch causes brown, crispy leaf margins and tips on trees and shrubs. Learn the environmental and biological cause…
Tomato Blight -- Early and Late: Identification and Treatment
Early blight and late blight on tomatoes look different and require different responses. Identify each disease and treat…
All problems guides
ProblemAnimal Damage to Plants: Deer, Rabbit, Vole, and Groundhog IDProblemAnthracnose on dogwoodProblemAnthracnose on sycamoreProblemAnthracnose on tomatoesProblemAphids on Kale: Identifying Cabbage Aphid and Managing Heavy InfestationsProblemAphids on Roses: Identification, Damage, and ControlProblemAphids on Tomatoes: Species, Damage, and What Controls WorkProblemAphids vs thrips: visual IDProblemApple scab: prevention and resistant cultivarsProblemAster yellows: the phytoplasma disease that distorts coneflowers and zinniasProblemBagworm on arborvitae and evergreensProblemBeneficial insects in the garden: ID guideProblemBlack Spot on Roses: Identification, Treatment, and PreventionProblemBlack knot on plum and cherryProblemBlight on Potatoes: Early Blight, Late Blight, and How to Tell Them ApartProblemBlossom Drop on Tomato and Pepper: Causes and FixesProblemBlossom end rot in tomatoes and peppers: it's not a diseaseProblemBotrytis (gray mold) on strawberriesProblemBotrytis blight on peoniesProblemBotrytis blight on tulips (tulip fire)ProblemBoxwood blight identification and quarantineProblemBrown Leaf Tips: Causes and FixesProblemBrown Leaves on Hydrangea: Causes and FixesProblemCabbage Worms on Broccoli and Kale: Control GuideProblemCedar-apple rust: lifecycle and managementProblemCedar-quince rustProblemCercospora leaf spot on hydrangeaProblemColorado potato beetleProblemCommon garden caterpillars: ID by damage and colorProblemCorn earworm on sweet cornProblemCucumber Beetle Control: Striped and Spotted SpeciesProblemCucumber beetles on squash and zucchiniProblemCutworm damage: signs and confirmationProblemDamping Off: Why Seedlings Keel Over and How to Stop ItProblemDeer vs rabbit vs vole damageProblemDeer-Resistant Perennials: What Actually Works in Suburban Long IslandProblemDowny mildew on cucumbersProblemDowny mildew on grapesProblemDowny mildew on impatiensProblemEarly Blight vs. Late Blight on Tomatoes: Identification and ManagementProblemEarly blight on potatoesProblemEarly blight on tomatoesProblemEmerald ash borer identification (vs lookalikes)ProblemEuropean corn borerProblemFire Blight on Pear and Apple: ID and TreatmentProblemFire blight on pearsProblemFlea beetles on cabbage familyProblemFlea beetles on eggplantProblemFrost Damage vs Fungal Damage on Leaves: How to Tell Them ApartProblemFruit Not Setting on Tomatoes, Peppers, and SquashProblemFusarium Wilt in Tomato: Symptoms and ManagementProblemFusarium wilt on strawberriesProblemFusarium wilt on tomatoes: identify, prevent, replaceProblemGopher damage and managementProblemGrub damage in lawn: when to treatProblemHoles in Leaves: Which Pest Is WhichProblemHow to Get Rid of Aphids Outdoors: What Actually WorksProblemHow to Get Rid of Slugs in the GardenProblemHow to Identify Herbicide Damage on PlantsProblemHow to identify Japanese knotweedProblemHow to identify bindweed vs morning gloryProblemHow to identify common lawn weedsProblemHow to identify garden thistlesProblemHow to identify poison ivy (leaves of three, not always)ProblemHow to identify poison oak (west coast)ProblemHow to identify poison sumacProblemHow to identify root rot vs drought stressProblemHow to identify rust diseases by hostProblemHow to identify stinging nettle (and its lookalikes)ProblemHow to identify the major leaf-spot diseasesProblemInvasive vines in eastern North America: ID and removalProblemIron vs nitrogen chlorosis: how to tellProblemJapanese beetle damage and control: what actually worksProblemLace bug on azalea and rhododendronProblemLate blight on potatoesProblemLate blight on tomatoesProblemLawn Rust Disease: Orange Powder on Grass BladesProblemLeaf Scorch: Causes, Identification, and TreatmentProblemLeaf Spot Diseases: Septoria, Alternaria, BacterialProblemLeaf Spot on Tomatoes: Septoria vs. Bacterial Speck and SpotProblemLeaf miner damage: which insectProblemMealybugs on Outdoor Ornamentals and CitrusProblemMealybugs on coleusProblemMexican bean beetleProblemMole vs vole damage in yardsProblemMy Plant Isn't Growing: 6 Reasons RankedProblemNutrient deficiencies: visual ID by leaf symptomProblemPeach Leaf Curl: Dormant Copper Spray Timing GuideProblemPeach tree borerProblemPlant galls: which are harmful, which aren'tProblemPlants Flowering Then Dying Back: Normal vs ProblemProblemPlants Wilting When the Soil Isn't Dry: Root Rot, Disease, and Transplant ShockProblemPowdery mildew on garden plants: identification and treatmentProblemRaspberry cane borerProblemRoot Rot in Outdoor Plants: Symptoms, Causes, and RecoveryProblemRoot-Bound Plants: When and How to Slice and ReplantProblemRust Disease on Plants: Roses, Hollyhock & BeansProblemRust on Hollyhocks: Managing the Most Common Hollyhock DiseaseProblemRust on Roses: Identification, Causes, and TreatmentProblemScale Insects on Shrubs, Fruit Trees & OrnamentalsProblemScale insects on magnoliaProblemScale insects: armored vs soft scaleProblemScale on camelliaProblemScale on euonymusProblemSeptoria leaf spot on tomatoesProblemSnail vs slug damage and behaviorProblemSnow Mold on Lawns: Pink & Gray Snow Mold GuideProblemSoil-borne pests: ID by plant symptomProblemSpider mite damage vs lookalikesProblemSpider mites on arborvitaeProblemSpider mites on beansProblemSpider mites on juniperProblemSpider mites on outdoor plants: dust mites in hot dry summersProblemSquash Vine Borer Treatment and PreventionProblemSquash bugs on pumpkin and winter squashProblemSunscald on Trees: Cherry, Maple & Fruit Tree BarkProblemTent caterpillars vs fall webworm vs bagwormProblemThrips on Roses, Vegetables, and OrnamentalsProblemThrips on onionsProblemThrips on rosesProblemTomato Blight -- Early and Late: Identification and TreatmentProblemTomato Cracking and Splitting: Causes and PreventionProblemTomato Fruit Problems: BER, Cracking, Catfacing, SunscaldProblemTomato Hornworm: Identification, Damage, and ControlProblemTransplant Shock: Symptoms, Timeline, and RecoveryProblemTree borer damage: ID by gallery patternProblemTree cankers: ID and tree-level disease riskProblemVerticillium Wilt: Crops, Trees, and Soil PersistenceProblemVerticillium wilt on Japanese mapleProblemVerticillium wilt on eggplantProblemVerticillium wilt on tomatoesProblemWhite Spots on Leaves: [Powdery Mildew](/problems/powdery-mildew/) vs Leaf Scorch vs Spider MitesProblemWhitefly on cabbage and kaleProblemWhitefly on tomatoesProblemWhy Are My Plants Leggy? Light, Water, and Timing CausesProblemWhy Isn't My Hydrangea Blooming? Six Real CausesProblemWild grape vs Virginia creeper vs poison ivy vinesProblemWilt diseases: bacterial vs fungal IDProblemWinter Burn on Boxwood, Holly & RhododendronProblemYellow Leaves on Plants: 8 Causes Ranked by LikelihoodProblemYellow Leaves on Tomato Plants: Causes and FixesProblem[Japanese Beetles](/problems/japanese-beetles/) on Grapes: Managing a Serious Feeding PestProblem[Japanese Beetles](/problems/japanese-beetles/) on Roses: Control Options and What Actually WorksProblem[Powdery Mildew](/problems/powdery-mildew/) on Cucumbers: Why It Happens and How to Stop ItProblem[Powdery Mildew](/problems/powdery-mildew/) on Peonies: Late-Season Identification and ManagementProblem[Powdery Mildew](/problems/powdery-mildew/) on Roses: Identification, Prevention, and TreatmentProblem[Powdery Mildew](/problems/powdery-mildew/) on Zucchini: Managing the Late-Season DeclineProblem[Spider Mites](/problems/spider-mites-outdoor/) on Cucumbers: Signs, Damage Thresholds, and Effective ControlsProblem[Spider Mites](/problems/spider-mites-outdoor/) on Tomatoes: Identification, Damage, and Control