Garden Disease & Pest Database

Late blight (Phytophthora infestans) is the most destructive disease of tomato and potato, capable of wiping out a crop in days during cool, wet weather. It caused the Irish potato famine and remains a serious threat for home and commercial growers alike.

🌡️ 10–25°C · humidity ≥90% · wet leaves / rain

Early blight (Alternaria solani) is a common warm-season disease of tomato and potato that builds through summer, starting on the oldest leaves and working upward, reducing yield and exposing fruit to sunscald.

🌡️ 20–32°C · humidity ≥75% · wet leaves / rain

Powdery mildew is a group of fungi affecting cucurbits, grapes, roses, squash and many ornamentals. Unusually, it thrives in warm, dry conditions with high humidity but does not need leaf wetness, making it common in late summer.

🌡️ 15–28°C · humidity ≥60%

Downy mildew (various Peronospora and Plasmopara species) attacks cucurbits, grapes, basil, lettuce and onions in cool, wet weather. Unlike powdery mildew it needs prolonged leaf wetness and spreads explosively in humid spells.

🌡️ 10–23°C · humidity ≥85% · wet leaves / rain

Gray mold (Botrytis cinerea) is a ubiquitous fungus attacking soft tissue of strawberries, grapes, tomatoes and ornamentals, especially in cool, damp, poorly ventilated conditions and on greenhouse crops.

🌡️ 5–22°C · humidity ≥90% · wet leaves / rain

Apple scab (Venturia inaequalis) is the most important disease of apples and crabapples in temperate climates, infecting leaves and fruit during wet spring weather and disfiguring the crop.

🌡️ 6–26°C · humidity ≥80% · wet leaves / rain

Black spot (Diplocarpon rosae) is the most common and serious disease of roses worldwide, defoliating bushes through warm, wet summers and weakening them before winter.

🌡️ 18–27°C · humidity ≥85% · wet leaves / rain

Anthracnose (Colletotrichum species) is a warm-wet-weather disease of beans, cucurbits, tomatoes, and many trees and shrubs, causing sunken fruit lesions that ruin marketable yield.

🌡️ 20–30°C · humidity ≥85% · wet leaves / rain

Rust fungi are a large group infecting beans, hollyhock, roses, daylilies, cereals and many plants, recognisable by powdery orange pustules and favoured by humid weather with cool nights.

🌡️ 10–24°C · humidity ≥85% · wet leaves / rain

Septoria leaf spot (Septoria lycopersici) is a major tomato disease in humid summers, causing heavy defoliation from the bottom up that exposes fruit and slashes yield.

🌡️ 20–26°C · humidity ≥90% · wet leaves / rain

Fusarium wilt (Fusarium oxysporum) is a soil-borne fungus that plugs the water-conducting tissue of tomatoes, melons, bananas and many crops, thriving in warm soils and persisting for years.

🌡️ 25–34°C · humidity ≥60%

Verticillium wilt (Verticillium dahliae) is a cool-season soil-borne wilt with a very wide host range including tomatoes, potatoes, maples and many trees, clogging vascular tissue and persisting in soil for over a decade.

🌡️ 18–27°C · humidity ≥60%

Clubroot (Plasmodiophora brassicae) is a soil-borne disease of cabbage, broccoli, kale and other brassicas that swells the roots into useless galls and persists in soil for up to 20 years.

🌡️ 12–27°C · humidity ≥70% · wet leaves / rain

White mold (Sclerotinia sclerotiorum) attacks beans, lettuce, carrots and over 400 plant species in cool, moist, dense canopies, producing hard black resting bodies that survive years in soil.

🌡️ 10–24°C · humidity ≥90% · wet leaves / rain

Cercospora leaf spot affects beets, chard, peppers, carrots and many crops in warm humid weather, causing rapid defoliation that reduces root and fruit size.

🌡️ 20–32°C · humidity ≥85% · wet leaves / rain

Peach leaf curl (Taphrina deformans) infects peach and nectarine trees during cool, wet spring weather as buds swell, distorting new growth and weakening trees over years.

🌡️ 7–19°C · humidity ≥85% · wet leaves / rain

Brown rot (Monilinia species) is the most damaging disease of stone fruit — peaches, plums, cherries and apricots — rotting blossoms and fruit in warm, humid weather near harvest.

🌡️ 18–28°C · humidity ≥85% · wet leaves / rain

Cedar-apple rust (Gymnosporangium) needs both junipers and apples to complete its life cycle, spotting apple foliage and fruit after wet spring weather when orange spores release from cedar galls.

🌡️ 8–24°C · humidity ≥85% · wet leaves / rain

Black rot (Guignardia bidwellii) is the most serious fungal disease of grapes in warm humid regions, destroying entire clusters in wet seasons if left unmanaged.

🌡️ 15–27°C · humidity ≥85% · wet leaves / rain

Damping-off (Pythium, Rhizoctonia and Fusarium) kills seedlings before or just after emergence in cold, wet, poorly drained or overcrowded conditions, a common setback for spring seed-starting.

🌡️ 5–20°C · humidity ≥90% · wet leaves / rain

Southern blight (Sclerotium rolfsii) is a hot-weather soil-borne fungus attacking tomatoes, peppers, beans and many vegetables at the stem base, common in warm humid climates.

🌡️ 25–35°C · humidity ≥80% · wet leaves / rain

Leaf mold (Passalora fulva) is a major greenhouse and high-tunnel tomato disease driven by high humidity and poor ventilation, rarely serious outdoors but devastating under cover.

🌡️ 18–27°C · humidity ≥85% · wet leaves / rain

Fire blight (Erwinia amylovora) is a destructive bacterial disease of apple, pear, quince and related plants that spreads rapidly during warm, humid bloom, killing blossoms, shoots and whole limbs.

🌡️ 21–30°C · humidity ≥70% · wet leaves / rain

Bacterial leaf spot (Xanthomonas and Pseudomonas) affects peppers, tomatoes, stone fruit and leafy greens in warm, wet, splashy weather, spreading fast through rain and overhead irrigation.

🌡️ 22–32°C · humidity ≥80% · wet leaves / rain

Bacterial wilt (Erwinia tracheiphila, spread by cucumber beetles, and Ralstonia in solanaceous crops) plugs the vascular system of cucurbits and tomatoes, causing irreversible collapse in warm weather.

🌡️ 25–37°C · humidity ≥70%

Bacterial canker (Clavibacter michiganensis in tomato; Pseudomonas in stone fruit) is a serious seed- and water-borne disease that causes wilting, cankers and fruit spotting in cool, wet conditions.

🌡️ 16–28°C · humidity ≥80% · wet leaves / rain

Crown gall (Agrobacterium tumefaciens) is a soil-borne bacterium that induces tumour-like galls on roots and stems of roses, fruit trees, grapes and many woody plants, entering through wounds.

🌡️ 20–30°C · humidity ≥60%

Bacterial speck (Pseudomonas syringae pv. tomato) is a cool, wet-weather tomato disease that blemishes fruit and spots foliage, most damaging early in the season and in spring transplants.

🌡️ 13–25°C · humidity ≥80% · wet leaves / rain

Mosaic viruses (Tobacco mosaic, Cucumber mosaic and relatives) infect tomatoes, peppers, cucurbits and many ornamentals, spread by handling, aphids and contaminated tools, with no cure once infected.

🌡️ Spread by handling, insects or soil — not weather-triggered

Tomato spotted wilt virus is spread by thrips and infects tomatoes, peppers, lettuce and hundreds of ornamentals worldwide, causing severe yield and quality loss with no cure.

🌡️ Spread by handling, insects or soil — not weather-triggered

Leaf curl viruses (such as Tomato yellow leaf curl) are whitefly-transmitted viruses that devastate tomatoes and peppers in warm climates, stunting plants and slashing fruit set.

🌡️ Spread by handling, insects or soil — not weather-triggered

Aphids are soft-bodied sap-sucking insects that multiply explosively in warm spring and summer weather on almost every crop, weakening plants and spreading viruses as they feed.

🌡️ 16–28°C

Spider mites are tiny sap-sucking arachnids that explode in numbers during hot, dry, dusty weather, especially on beans, tomatoes, cucumbers and houseplants, and are favoured by drought stress.

🌡️ 27–40°C · dry air ≤55%

Whiteflies are tiny sap-sucking insects that swarm up in clouds when plants are disturbed, thriving in warm weather and greenhouses on tomatoes, brassicas and ornamentals, and spreading viruses.

🌡️ 21–33°C

Scale insects are immobile sap-suckers that attach to stems and leaves of fruit trees, citrus, houseplants and shrubs under protective waxy shells, slowly draining vigour.

🌡️ 18–34°C

Caterpillars — the larvae of moths and butterflies such as cabbage worms, hornworms and loopers — chew foliage and fruit of vegetables and ornamentals through the warm season.

🌡️ 15–33°C

Slugs and snails are night-feeding molluscs that thrive in cool, wet, shady conditions, shredding seedlings, leafy greens and soft growth, and are most destructive after rain.

🌡️ 5–22°C · humidity ≥80% · wet leaves / rain

Thrips are slender rasping insects that scar flowers and foliage of vegetables, fruit and ornamentals in warm dry weather and greenhouses, and transmit damaging viruses such as spotted wilt.

🌡️ 20–35°C · dry air ≤60%

Japanese beetles are metallic green-and-copper beetles that swarm in midsummer to skeletonise the leaves of roses, grapes, fruit trees and hundreds of plants, while their grubs damage lawn roots.

🌡️ 21–35°C

The Colorado potato beetle is the most important insect pest of potatoes and also attacks tomatoes, peppers and eggplant, defoliating plants rapidly and notorious for developing insecticide resistance.

🌡️ 18–33°C

The codling moth is the key pest of apples and pears worldwide; its larvae tunnel into the core of developing fruit, causing the classic 'wormy apple' and major harvest loss.

🌡️ 15–32°C

Mealybugs are soft sap-sucking insects coated in white waxy fluff that infest houseplants, citrus, grapes and greenhouse crops, thriving in warm, sheltered conditions year-round indoors.

🌡️ 20–32°C

Squash bugs are shield-shaped sap-sucking insects that attack squash, pumpkins and other cucurbits through summer, causing wilting that can be mistaken for bacterial wilt and killing young plants.

🌡️ 21–35°C

Nitrogen deficiency is one of the most common nutrient problems, since nitrogen is mobile and leaches readily from soil, leaving plants pale and slow-growing, especially in wet springs and sandy soils.

🌡️ Spread by handling, insects or soil — not weather-triggered

Iron chlorosis is a common deficiency in high-pH (alkaline) and waterlogged soils, where iron becomes unavailable even when present, affecting blueberries, rhododendrons, citrus and many ornamentals.

🌡️ Spread by handling, insects or soil — not weather-triggered

Magnesium deficiency is widespread on sandy, acidic and heavily potassium-fertilised soils, common in tomatoes, potatoes and roses, since magnesium is the central atom of chlorophyll.

🌡️ Spread by handling, insects or soil — not weather-triggered

Potassium deficiency reduces fruit quality and disease resistance, common on sandy and light soils and in heavy-fruiting crops like tomatoes, potatoes and fruit trees.

🌡️ Spread by handling, insects or soil — not weather-triggered

Blossom end rot is a physiological disorder of tomatoes, peppers, squash and melons caused by a calcium shortage in the fruit, usually triggered by uneven watering rather than low soil calcium.

🌡️ Spread by handling, insects or soil — not weather-triggered

Sunscald is a physiological injury to fruit and bark from intense sun and heat, common on tomatoes, peppers and apples when foliage is thin from pruning, disease or defoliation.

🌡️ 32–45°C · dry air ≤50%

Fruit cracking is a physiological disorder of tomatoes, cherries, plums and melons caused by rapid water uptake after dry spells, especially when heavy rain follows drought near ripening.

🌡️ wet leaves / rain