Tomatoes

White fungal growth reduces photosynthesis; leaves may yellow, distort, brown, and die early, weakening plants and reducing fruit quality.

Favored By

Warm days, cool nights, high humidity, crowded growth, shade, and dry foliage; unlike many diseases, free water is not required.

What It Looks Like

White to gray powdery patches on either leaf surface, stems, petioles, or buds; patches enlarge and may cover whole leaves.

Prevention

Choose resistant cultivars; provide full sun and airflow; space and prune plants; avoid excess nitrogen; remove infected residue.

Management

Remove badly affected leaves early; apply horticultural oil, sulfur, potassium bicarbonate, or another fungicide labeled for the crop before disease is severe. Do not apply oils and sulfur close together.

Seeds rot before emergence or young seedlings collapse, producing thin stands and sudden losses in flats or garden rows.

Favored By

Cold or waterlogged soil, contaminated mix or containers, poor drainage, deep sowing, dense seedlings, low light, and overwatering.

What It Looks Like

Pre-emergence seeds become soft and brown; emerged seedlings develop a water-soaked or pinched stem at the soil line and topple.

Prevention

Use sterile seed-starting mix and clean containers; sow at the proper depth; provide warmth, drainage, light, and airflow; avoid crowding and overwatering.

Management

Discard affected seedlings and nearby mix; reduce watering; improve light and airflow. Fungicides have limited value after collapse and must be specifically labeled.

Leaf, stem, and fruit or tuber lesions cause progressive defoliation, sunscald, reduced yield, and storage losses.

Favored By

Warm weather, repeated rain or irrigation, long leaf wetness, plant stress, older foliage, infected residue, and volunteer nightshades.

What It Looks Like

Brown leaf spots with target-like concentric rings and yellow margins, beginning low on plants; dark sunken stem or fruit lesions may also show rings.

Prevention

Use certified seed and healthy transplants; rotate away from nightshades; mulch; stake plants; use drip irrigation; remove volunteers and residue.

Management

Remove heavily infected lower leaves; maintain nutrition and irrigation; apply a labeled protectant fungicide early when weather and disease history justify it.

A fast-moving oomycete disease destroys foliage, stems, tomato fruit, and potato tubers and can collapse plantings within days.

Favored By

Cool, wet weather, high humidity, frequent rain or fog, infected potato seed pieces, volunteer potatoes, and windborne spores.

What It Looks Like

Irregular water-soaked gray-green leaf lesions turn brown; white fuzzy growth may form at lesion edges underneath; stems blacken and tomato fruit develops firm greasy-brown patches.

Prevention

Plant certified disease-free potatoes and resistant cultivars; destroy cull piles and volunteers; space plants; avoid overhead irrigation; monitor regional alerts.

Management

Immediately remove and bag affected plants; do not compost them. Preventive fungicides must be applied before or at first risk and rotated according to label and Extension guidance.

Numerous leaf spots merge, causing lower leaves to yellow and drop; exposed tomato fruit may sunscald and yield declines.

Favored By

Warm, wet or humid weather, splashing water, infected crop debris, volunteer tomatoes, dense foliage, and handling wet plants.

What It Looks Like

Many small circular spots with tan or gray centers, dark margins, and tiny black fruiting bodies; symptoms usually begin on lower leaves.

Prevention

Rotate crops; remove tomato debris and volunteers; mulch; stake and prune for airflow; use drip irrigation; avoid working among wet plants.

Management

Remove infected lower leaves early; sanitize tools; use a labeled protectant fungicide if disease continues to spread under favorable weather.

Leaf, stem, and especially fruit infections produce sunken rots, reduce marketable harvest, and continue after picking.

Favored By

Warm wet weather, splashing rain, overhead irrigation, infected seed or residue, dense canopies, and overripe fruit.

What It Looks Like

Round sunken dark lesions on ripe fruit, sometimes with concentric rings of black dots or salmon-pink spore masses; leaves and stems may spot or canker.

Prevention

Use disease-free seed and resistant cultivars; rotate; mulch; stake plants; irrigate at soil level; harvest promptly; remove mummified fruit and debris.

Management

Pick and discard infected fruit; avoid handling wet plants; cool harvested produce promptly; apply crop-labeled fungicides preventively when local guidance recommends.

Blossoms, leaves, stems, and fruit rot; infections often enter through flowers, wounds, or dying tissue and can spread in storage.

Favored By

Cool to moderate humid weather, prolonged leaf wetness, crowding, poor airflow, dead blossoms, overripe fruit, and plant wounds.

What It Looks Like

Soft tan-to-brown rot covered by fuzzy gray spores; infected blossoms collapse and stems may develop pale cankers.

Prevention

Space and prune plants; ventilate protected growing areas; use drip irrigation; remove dead flowers and damaged tissue; harvest before fruit becomes overripe.

Management

Remove and discard infected tissue without shaking spores; lower humidity; sanitize harvest containers; use a labeled fungicide only when timed preventively.

Soilborne vascular infection blocks water movement, causing one-sided yellowing, chronic wilt, stunting, and eventual plant death.

Favored By

Warm soil, susceptible cultivars, infested soil or transplants, root injury, continuous host cropping, and some nematode damage.

What It Looks Like

Lower leaves yellow and wilt, often on one side; brown discoloration appears in vascular tissue when the lower stem is split lengthwise.

Prevention

Plant resistant cultivars and clean transplants; rotate with nonhosts; avoid moving infested soil; sanitize tools; manage root-knot nematodes.

Management

Remove entire infected plants and roots; do not compost. There is no curative home-garden treatment; use resistant varieties and long rotations in future seasons.

Vascular infection causes gradual yellowing, wilt, stunting, and dieback in many vegetables, berries, and ornamentals.

Favored By

Cool to moderate soil, susceptible hosts, infested soil, repeated planting of host crops, and plant stress.

What It Looks Like

Lower leaves yellow from margins inward, often in V-shaped areas; plants wilt gradually and stem vascular tissue may show light brown streaking.

Prevention

Choose resistant cultivars; rotate with nonhosts or grasses; control susceptible weeds; avoid moving soil; maintain balanced fertility and irrigation.

Management

Remove infected plants; no cure exists. Soil solarization may reduce inoculum in hot climates; replant with resistant or nonhost crops.

The pathogen girdles stems at the soil line and rots crowns and roots, causing sudden wilt and plant collapse across a wide host range.

Favored By

Hot, humid weather, moist soil, dense mulch or debris against stems, poor airflow, and repeated susceptible crops.

What It Looks Like

White fanlike fungal growth at the stem base and nearby soil, followed by numerous mustard-seed-like tan to brown sclerotia.

Prevention

Rotate with nonhosts such as corn or other grasses; improve drainage; keep mulch away from crowns; remove debris; avoid moving contaminated soil.

Management

Remove plants plus surrounding soil before sclerotia spread; deep burial may help in tilled areas; soil solarization can reduce survival in hot regions.

Stem and crown infections cause watery rot, wilting, lodging, and plant death in beans, lettuce, tomatoes, cucurbits, and many other crops.

Favored By

Cool moist weather, dense canopies, prolonged leaf wetness, poor airflow, flowering plants, and soils containing long-lived sclerotia.

What It Looks Like

Water-soaked lesions become bleached and covered with cottony white growth; hard irregular black sclerotia form inside or on stems.

Prevention

Rotate to grasses or other nonhosts; space and stake plants; use drip irrigation; control broadleaf weeds; remove infected plants before sclerotia mature.

Management

Pull and discard infected plants and nearby debris; reduce canopy moisture; avoid cultivating contaminated soil into new beds; fungicides are preventive, not curative.

Roots, crowns, stems, leaves, and fruit may rot; plants wilt suddenly and whole beds can collapse after saturated conditions.

Favored By

Warm wet weather, poorly drained or flooded soil, standing water, contaminated irrigation water, and repeated susceptible vegetables.

What It Looks Like

Dark water-soaked crown or stem lesions, brown rotted roots, sudden wilt, leaf blight, and firm water-soaked fruit rot sometimes covered with white growth.

Prevention

Use raised beds and well-drained sites; prevent runoff into beds; use drip irrigation; rotate; sanitize equipment; choose resistant cultivars where available.

Management

Remove infected plants and fruit; improve drainage immediately; avoid moving wet soil. Crop-labeled fungicides must be used preventively and resistance-managed.

Leaf, stem, and fruit spotting causes defoliation, sunscald, blemished fruit, and reduced yield.

Favored By

Warm wet weather, wind-driven rain, infected seed or transplants, overhead irrigation, plant wounds, and handling wet foliage.

What It Looks Like

Small dark water-soaked leaf spots become brown or black and may have yellow halos; pepper fruit has raised scabby spots and tomato fruit has rough lesions.

Prevention

Use pathogen-tested seed and clean transplants; rotate; mulch; stake plants; use drip irrigation; disinfect stakes; avoid saving seed from diseased plants.

Management

Remove badly infected plants or leaves; avoid copper overuse and follow local resistance guidance; sprays are preventive and cannot repair existing lesions.

Small leaf and fruit lesions cause defoliation and cosmetic damage, especially during cool wet springs.

Favored By

Cool moist weather, infected seed or transplants, splashing rain, overhead irrigation, crop residue, and wet plant handling.

What It Looks Like

Tiny dark brown to black leaf spots often have yellow halos; green fruit develops very small superficial black specks without deep scabs.

Prevention

Use clean seed and transplants; rotate; remove volunteers and residue; mulch; use drip irrigation; sanitize stakes and tools.

Management

Remove infected material early; avoid working wet plants. Copper-based sprays may suppress new infection when applied preventively according to label.

Wounded vegetables and storage organs rapidly become watery, foul-smelling, and unmarketable in the garden or after harvest.

Favored By

Warm wet conditions, wounds, insect injury, contaminated tools or wash water, poor ventilation, and warm storage.

What It Looks Like

Tissue becomes soft, water-soaked, cream to tan, and collapses into a wet mass; outer skin may remain briefly intact and odor is often strong.

Prevention

Prevent wounds; control insects; harvest in dry weather; sanitize tools and containers; cool produce quickly; provide drainage and ventilation.

Management

Remove rotting produce and contaminated debris; disinfect containers; do not store damaged vegetables with sound produce. No spray cures established soft rot.

Systemic viruses stunt plants, distort leaves and fruit, reduce yield, and persist for the plant's life.

Favored By

Aphids or other vectors, infected transplants or seed for some viruses, nearby weeds, continuous host plants, and mechanical sap transmission.

What It Looks Like

Light- and dark-green mosaic, yellow mottling, rings, shoestring or curled leaves, stunting, and bumpy or color-broken fruit; symptoms vary by virus and crop.

Prevention

Use virus-free seed and transplants; plant resistant cultivars; control weeds; use reflective mulch where practical; sanitize hands and tools.

Management

Remove symptomatic plants promptly; manage vectors early but recognize insecticides may not stop rapidly transmitted viruses. No treatment cures an infected plant.

A systemic virus causes stunting, bronzing, necrosis, ringspots, uneven fruit ripening, and plant death in many vegetables and ornamentals.

Favored By

Thrips vectors, infected weeds or ornamentals, warm protected growing areas, susceptible transplants, and overlapping host crops.

What It Looks Like

Young leaves may bronze or show dark streaks; growing tips die; tomato fruit develops concentric yellow, green, or brown rings.

Prevention

Use resistant tomato cultivars; inspect transplants; remove weed and ornamental reservoirs; exclude or monitor thrips; separate vegetable starts from flowers.

Management

Remove infected plants immediately; manage thrips with an integrated program. There is no cure, and late vector control will not reverse systemic infection.

Sap-feeding colonies distort tender growth, cause yellowing and sticky honeydew, and may transmit plant viruses.

Favored By

Soft new growth, excess nitrogen, sheltered plants, and warm moderate weather.

What It Looks Like

Tiny (about 1/16–1/8 in), soft, pear-shaped insects; green, black, yellow, gray, or pink; two tailpipe-like cornicles.

Prevention

Avoid excess nitrogen; inspect leaf undersides; conserve lady beetles, lacewings, hoverflies, and parasitoid wasps; control ants that protect aphids.

Management

Knock off with water; prune badly infested tips; use insecticidal soap or horticultural oil with thorough contact coverage. Repeat only as label directs.

Adults and nymphs suck sap, yellow leaves, reduce vigor, and excrete honeydew that supports sooty mold.

Favored By

Warm protected sites, greenhouses, dense foliage, weeds, and heavily fertilized tender growth.

What It Looks Like

Adults are tiny white, mothlike insects that flutter when disturbed; nymphs are flat, oval scales on leaf undersides.

Prevention

Inspect transplants; remove infested leaves and weeds; use screens in protected growing; avoid broad-spectrum insecticides that kill natural enemies.

Management

Use yellow sticky cards for monitoring; vacuum adults on small plantings; apply insecticidal soap or horticultural oil to leaf undersides.

Rasping-sucking feeding scars leaves, buds, flowers, and fruit; some species transmit viruses.

Favored By

Hot, dry weather; flowers and tender growth; weeds and plant debris; stressed plants.

What It Looks Like

Very slender, usually 1/25–1/8 in, yellow, tan, brown, or black; adults have narrow fringed wings.

Prevention

Start with clean plants; remove weeds and spent blossoms; keep plants evenly watered; conserve minute pirate bugs and other predators.

Management

Dislodge with water; remove heavily damaged tissue; use insecticidal soap, horticultural oil, or spinosad where labeled, timed to susceptible stages.

Mites remove cell contents, causing pale stippling, bronzing, leaf drop, and fine webbing during heavy infestations.

Favored By

Hot, dry, dusty conditions; drought-stressed plants; excess nitrogen; loss of predatory mites from broad-spectrum sprays.

What It Looks Like

Minute, eight-legged mites, yellow-green to reddish, usually with two dark body spots; eggs are round; fine webbing may be visible.

Prevention

Reduce dust; water plants adequately; inspect leaf undersides; avoid unnecessary broad-spectrum insecticides; isolate infested transplants.

Management

Hose leaf undersides; remove badly infested leaves; use insecticidal soap or horticultural oil. Ensure contact and repeat per label because eggs survive.

Adults chew numerous small shot holes in leaves; seedlings can be stunted or killed. Some larvae feed on roots.

Favored By

Warm sunny weather, young seedlings, nearby weeds or crop residue, and repeated planting of susceptible crops.

What It Looks Like

Tiny (about 1/16–1/8 in), shiny dark or striped beetles with enlarged hind legs that jump when disturbed.

Prevention

Use row cover immediately after planting; remove weeds and residues; rotate crops; plant vigorous transplants or delay planting where practical.

Management

Remove cover at flowering when pollination is needed; use labeled kaolin clay or insecticides only when feeding threatens establishment.

Night-feeding caterpillars sever seedlings at soil level; climbing species also feed on foliage and fruit.

Favored By

Weedy ground, plant residue, green manure, and recently converted sod; small transplants are most vulnerable.

What It Looks Like

Smooth, stout, gray, brown, green, or black caterpillars, often striped or spotted; curl into a C when disturbed.

Prevention

Remove weeds and residue before planting; till before planting and in fall; use compost rather than fresh green manure; place collars around transplants.

Management

Search soil near damaged plants at dusk and handpick; treat small larvae with a labeled biological or insecticide only when damage is active.

Large caterpillars rapidly defoliate tomatoes and relatives and may chew green fruit.

Favored By

Warm summer weather, nightshade-family crops, and nearby weeds such as horsenettle.

What It Looks Like

Large green caterpillars up to 4 in; diagonal white markings; a horn projects from the rear. Tobacco hornworm has red horn, tomato hornworm usually dark.

Prevention

Till soil after harvest; remove nightshade weeds; inspect stems and leaf undersides; preserve parasitoid wasps.

Management

Handpick; leave parasitized larvae bearing white wasp cocoons; apply Bacillus thuringiensis var. kurstaki or spinosad to small larvae where labeled.

Adults and larvae consume potato, eggplant, and related foliage and can completely defoliate plants.

Favored By

Repeated nightshade crops in the same area, volunteer potatoes, and nearby overwintering sites.

What It Looks Like

Rounded yellow-orange adult with 10 black wing stripes; humpbacked red-orange larvae with two rows of black spots.

Prevention

Rotate nightshade crops as far as practical; remove volunteers; use straw mulch; inspect early for orange egg masses.

Management

Crush eggs and handpick adults and larvae; use Bt tenebrionis products where available or spinosad where labeled; resistance is common.

Larvae tunnel between leaf surfaces, creating serpentine or blotchy mines that reduce photosynthesis and market quality.

Favored By

Warm weather, susceptible leafy crops, weeds, and broad-spectrum insecticide use that kills parasitoids.

What It Looks Like

Tiny dark flies are seldom noticed; pale legless larvae live inside leaves; mines are winding trails or translucent blotches.

Prevention

Use row cover; remove host weeds; inspect transplants; remove mined leaves before larvae exit; conserve parasitoid wasps.

Management

Crush larvae within mines or remove leaves; insecticides often miss protected larvae, so target adults/young larvae only with labeled selective products.

Larvae feed in corn ear tips and bore into tomato, pepper, bean, and other fruit, contaminating produce.

Favored By

Warm weather, late plantings, continuous flowering hosts, and moth migration from southern areas.

What It Looks Like

Variable green, tan, pink, or brown caterpillar with stripes and tiny dark spines; adult moth is tan with a dark spot.

Prevention

Plant early where appropriate; use tight-husked corn cultivars; remove damaged fruit; monitor moth flights and eggs; conserve natural enemies.

Management

Handpick from tomatoes and peppers; use Bt or spinosad on small exposed larvae where labeled; treatments are ineffective after larvae enter ears or fruit.

Adults and nymphs pierce fruit and vegetables, causing dimpling, corky spots, discoloration, and malformed produce.

Favored By

Warm seasons, wooded edges, diverse fruiting hosts, and nearby overwintering structures.

What It Looks Like

Shield-shaped mottled brown bug about 5/8 in; alternating light-dark marks on abdomen edge and white bands on antennae.

Prevention

Remove weeds and alternate hosts near production where practical; use fine netting; seal buildings to reduce overwintering; conserve egg parasitoids.

Management

Handpick or knock into soapy water; use traps for monitoring rather than control; apply labeled insecticides only when repeated feeding threatens crops.

Microscopic roundworms induce root galls, restricting water and nutrient uptake and causing stunting, yellowing, and midday wilt.

Favored By

Warm sandy soil, susceptible crops, contaminated transplants or soil, and repeated host crops.

What It Looks Like

Microscopic; diagnosis relies on swollen knots or galls on roots, often with a weak uneven crop canopy.

Prevention

Use clean transplants; grow resistant cultivars; rotate with poor hosts; solarize soil in hot climates; add organic matter and clean tools.

Management

Remove heavily infested roots; use resistant crops and rotation over multiple seasons; soil-applied products are limited and must be labeled for home gardens.

Larvae feed on fungi and fine roots in seed-starting mix, weakening seedlings; adults are mostly a nuisance.

Favored By

Continuously wet organic potting media, algae, decaying roots, and poor drainage.

What It Looks Like

Tiny dark mosquito-like flies; larvae are clear-white with shiny black heads and live in the top layer of moist mix.

Prevention

Allow the surface to dry between watering; improve drainage and airflow; use clean pasteurized media; remove algae and dead tissue.

Management

Use yellow sticky cards for adults; apply Bacillus thuringiensis israelensis as a soil drench according to label; beneficial nematodes may suppress larvae.

Pull seedlings, eat newly sown seed, peck ripening fruit, and damage corn or berries.

Favored By

Visible seed, ripening fruit, nearby roosts, and unprotected beds or small fruit plantings.

What It Looks Like

Species vary; identify by tracks, droppings, peck marks, missing seed, and time of activity.

Prevention

Use secured bird netting with openings that cannot entangle wildlife; row cover seedlings; reflective or moving deterrents work best when varied.

Management

Exclude during the vulnerable period; harvest promptly; avoid toxic baits. Federal and state protections apply to many bird species.