Rhubarb

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.

For Rhubarb: Reviewed Research Library baseline; local occurrence and treatment timing vary.

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.

For Rhubarb: Reviewed Research Library baseline; local occurrence and treatment timing vary.

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.

For Rhubarb: Reviewed Research Library baseline; local occurrence and treatment timing vary.

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.

For Rhubarb: Reviewed Research Library baseline; local occurrence and treatment timing vary.

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.

For Rhubarb: Reviewed Research Library baseline; local occurrence and treatment timing vary.

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.

For Rhubarb: Reviewed Research Library baseline; local occurrence and treatment timing vary.

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.

For Rhubarb: Reviewed Research Library baseline; local occurrence and treatment timing vary.

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.

For Rhubarb: Reviewed Research Library baseline; local occurrence and treatment timing vary.

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.

For Rhubarb: Reviewed Research Library baseline; local occurrence and treatment timing vary.

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.

For Rhubarb: Reviewed Research Library baseline; local occurrence and treatment timing vary.

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.

For Rhubarb: Reviewed Research Library baseline; local occurrence and treatment timing vary.

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.

For Rhubarb: Reviewed Research Library baseline; local occurrence and treatment timing vary.

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.

For Rhubarb: Reviewed Research Library baseline; local occurrence and treatment timing vary.

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.

For Rhubarb: Reviewed Research Library baseline; local occurrence and treatment timing vary.

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.

For Rhubarb: Reviewed Research Library baseline; local occurrence and treatment timing vary.

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.

For Rhubarb: Reviewed Research Library baseline; local occurrence and treatment timing vary.