Lettuce

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.

Rapid foliar blight reduces plant vigor and yield; severe infections can kill leaves while stems and fruit often remain initially intact.

Favored By

Cool to moderate temperatures, prolonged leaf wetness, high humidity, cloudy weather, dense foliage, and windborne spores.

What It Looks Like

Angular yellow or pale-green spots on upper leaf surfaces with gray, purple, or dark downy growth beneath, most visible on humid mornings.

Prevention

Plant resistant cultivars where available; improve airflow; use drip irrigation; avoid overhead watering late in the day; remove volunteer hosts.

Management

Remove infected leaves or plants when practical; monitor regional forecasts for cucurbit downy mildew; use a crop-labeled preventive fungicide when local risk is high.

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 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.

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.

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.

Phytoplasmas disrupt growth in carrots, lettuce, herbs, flowers, and many weeds, producing stunting, sterility, and poor-quality roots or heads.

Favored By

Aster leafhopper transmission, abundant weed hosts, warm weather that supports vectors, and overlapping susceptible crops.

What It Looks Like

Yellowed upright shoots, excessive branching or witches'-brooms, distorted green flowers, stunted roots, and orange or purple discoloration in carrots.

Prevention

Control broadleaf weeds; remove volunteer hosts; use row cover on vulnerable crops before leafhopper arrival; monitor regional leafhopper activity.

Management

Pull and discard infected plants promptly so leafhoppers cannot acquire the pathogen; manage leafhoppers when local thresholds and guidance justify treatment.

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.

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.

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.

Larvae chew ragged holes and may bore into cabbage heads; frass contaminates produce.

Favored By

Warm weather, continuous brassica plantings, and southern migrations of adult moths.

What It Looks Like

Green caterpillar with white side stripes and only two pairs of mid-abdominal prolegs; moves by looping its body.

Prevention

Use insect netting; destroy crop residues; remove crucifer weeds; scout weekly for eggs and small larvae.

Management

Handpick; apply Bt kurstaki while larvae are small or spinosad where labeled; rotate insecticide modes if repeated treatment is necessary.

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.

They rasp irregular holes in leaves, stems, seedlings, and low fruit and leave silvery slime trails.

Favored By

Moist shade, dense mulch, weeds, boards, stones, and frequent evening irrigation.

What It Looks Like

Soft-bodied mollusks; snails carry shells while slugs do not; active mostly at night or during wet weather.

Prevention

Water in morning; improve airflow and drainage; remove hiding places and weeds; keep mulch away from seedling stems; use barriers where practical.

Management

Handpick at night; use board traps; apply iron phosphate bait according to label and protect it from children, pets, and wildlife.

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 chew seeds, roots, and underground stems or tubers, causing poor stands and holes in potatoes and root crops.

Favored By

Recently converted sod or weedy ground, cool moist soil, and high organic matter.

What It Looks Like

Slender, hard-bodied, shiny yellow to brown larvae with three pairs of small legs; adults are click beetles.

Prevention

Avoid planting susceptible crops immediately after sod; till to expose larvae; control grassy weeds; use bait stations before planting to assess risk.

Management

Trap with buried potato or carrot pieces and remove larvae; rotate to less susceptible crops; rescue treatments after planting are generally ineffective.

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.

Browse foliage, buds, flowers, and fruit; damage often occurs high above the ground with ragged torn stems.

Favored By

High deer density, drought or winter food shortage, gardens near woods, and unfenced plantings.

What It Looks Like

Large hoofed mammal; cloven tracks and pellet droppings; browsing can reach roughly 6 ft.

Prevention

Install an 8-ft deer fence or properly designed electric fence; use cages and netting; choose less-preferred plants while recognizing none are deer-proof.

Management

Exclude first; rotate repellents labeled for edible crops and reapply after rain; protect young trees with guards. Follow local wildlife laws.

Clip seedlings and tender stems, browse leafy greens and beans, and gnaw bark in winter.

Favored By

Dense cover, brush piles, fence gaps, drought, and abundant tender vegetation.

What It Looks Like

Small mammal with long ears and short white tail; leaves round pellets and clean, angled cuts close to the ground.

Prevention

Use 1-in poultry mesh at least 2 ft high with bottom buried 3–6 in; remove nearby cover; use trunk guards.

Management

Exclude and protect individual beds; use repellents labeled for edible crops; trapping or lethal control is regulated and should follow local law.

Consumes large amounts of vegetables and can flatten plants; burrows may undermine beds or structures.

Favored By

Gardens near field edges, brush, sheds, stone piles, and accessible fence bottoms.

What It Looks Like

Large stocky brown-gray rodent with short bushy tail; wide burrow entrances and tracks with four front toes and five rear toes.

Prevention

Use sturdy 3-ft wire fencing with 12 in buried or bent outward; add an outward electric wire; remove brush and block access under structures.

Management

Exclusion is most reliable; harassment and repellents have limited persistence; trapping or euthanasia must comply with state and local law.

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.