Tatsoi

A soilborne rot that starts on the lower leaves touching the ground, producing rusty-brown sunken lesions that spread up into the head. Affected leaves turn slimy and a brown, dry rot can move into the heart of the plant. It is favored by warm, humid conditions and by heads sitting on wet soil.

Triggers: Rhizoctonia solani is most active in warm, humid weather. Infection begins where lower leaves contact moist soil, so dense heads and wet ground raise risk.

Risk fades when: Drier soil and foliage slow spread. Three dry days reduces active risk, though rotted tissue stays damaged.

A cool-weather foliar disease most damaging on seedlings and young plants. It shows as faint yellow spots on the upper leaf surface with a white to gray fuzzy growth on the underside. On heads and curds it can cause dark speckling that downgrades quality. It is driven by cool temperatures, leaf wetness, and high humidity.

Triggers: Favored by cool temperatures and prolonged leaf wetness or high humidity. Most serious on seedlings, where it can kill young plants; on older plants it spots leaves and can speckle heads.

On Tatsoi: Cool, humid weather and dense plantings can spot and collapse leaves.

Prevention: Improve airflow, water at the base, and remove badly infected foliage.

Risk fades when: Warm, dry weather suppresses it. Three dry days with highs above 75°F exits the active window; spotted leaves stay damaged.

Flea beetles are small (1/16-inch) shiny beetles that jump like fleas when disturbed. They chew small round 'shothole' or 'pinhole' damage in leaves and can destroy emerging cotyledons of broccoli or eggplant in 24 hours. Most species are host-family specific — crucifer flea beetle on brassicas, tuber flea beetle on potatoes, eggplant flea beetle on solanaceous crops.

Triggers: Overwinter as adults in leaf litter and field margins. Active at mid- to late-spring temperatures. Warm winter → higher next-spring populations (NC State). Hot dry conditions amplify damage on stressed seedlings.

On Tatsoi: Small beetles chew shot holes in young brassica leaves, especially in warm dry weather.

Prevention: Use row cover on young plants and keep growth moving with even moisture.

Risk fades when: UMN: 1-2 generations in Minnesota, populations crash after mid-June

Fuzzy gray mold on flowers, fruit, and wounded tissue. It thrives in cool, humid, enclosed spaces — University of Minnesota notes this is unlikely to be a problem in open home gardens and rare even in field tomatoes. It's mostly a greenhouse and high-tunnel concern, included here because SoilStack supports those growing environments.

Triggers: Develops at 60-75°F with humidity above 80%. Infection requires 4-6 hours of standing water on the plant tissue. UMN's data shows it's unlikely in open home gardens.

Risk fades when: Temperatures above 82°F suppress growth and spore production. That's the published threshold.

Microscopic soil-dwelling roundworms that burrow into plant roots and cause swollen knots (galls). Above ground, the plant looks stunted, yellowed, and wilted even with plenty of water. They attack over 2,000 plant species, so almost nothing is safe. They're most active in warm soil (70-85°F) and do more damage in sandy soils, where they move easily. Once a bed has them, populations stick around for years.

Triggers: Soil temperatures of 70-85°F are ideal for them; below 60°F they go dormant. Sandy soils make it easy for them to move and reproduce, while heavy clay slows them down considerably. In warm soil, a full generation completes in about 27 days.

Risk fades when: Activity drops sharply once soil cools below 60°F. Damage stops accumulating for the season, but the population stays in the soil and returns when warmth does.

A foliar disease that produces small, irregular tan to brown spots peppered with tiny dark fruiting bodies, usually starting on the older outer leaves. Heavy spotting reduces quality and can cause leaves to yellow and die. It spreads in wet weather and from infected seed or debris.

Triggers: Wet foliage and splashing water spread the spores. Favored by extended leaf wetness; spots carry tiny dark fruiting bodies visible up close.

Risk fades when: Dry foliage stops new spread. Three dry days exits the active window; existing spots remain.

Slugs and snails are nocturnal mollusks that chew irregular holes in leaves and clip off succulent seedlings. They leave characteristic silvery slime trails. Hermaphroditic and prolific, brown garden snails lay around 80 eggs per month for up to six clutches per year.

Triggers: Active at night and early morning in damp conditions. Coastal CA and southeast — active year-round. Spring rains and dense ground cover (mulch, debris, weeds) create harborage.

Risk fades when: Hot, dry summer weather drives slugs and snails into inactivity, so risk drops sharply once conditions turn warm and dry; populations are highest in cool, wet spring and fall, and in mild-winter coastal regions they can stay active year-round (UMN Extension, Penn State, UC IPM).

Thrips are tiny (1/16 inch) slender insects with fringed wings that puncture and rasp leaf surfaces, leaving silver stippling with black frass dots. The biggest concern is virus vectoring: western flower thrips is the principal vector of tomato spotted wilt virus (TSWV) and impatiens necrotic spot virus (INSV), which affect more than 600 plant species. Greenhouse and high tunnel infestations can be devastating.

Triggers: Hot dry weather; greenhouse/high tunnel environments. Female lays eggs inside leaf tissue. 2 larval stages feed; 2 non-feeding pupal stages in soil/litter. Lifecycle 10-21 days. Many overlapping generations. Bridge crops (spring wheat, peach, strawberry per NC State) build populations before vegetable hosts available.

Risk fades when: Infestations are worst in hot, dry weather; cool conditions slow development and heavy rain or overhead irrigation knocks populations down sharply, so risk fades as the weather turns cool and wet and rebuilds the following spring (UK Entomology, Cornell IPM).

Tiny sap-sucking insects that erupt off the leaf in a white cloud when you brush the plant. Despite the name they are not flies at all - they are Hemiptera, relatives of aphids, scales and mealybugs, and the name comes from the mealy white wax coating the adult's wings and body. They pierce the phloem and drain sap, so heavy populations yellow the leaves, dry them, and drop them. The bigger nuisance is honeydew: a sticky sugary excretion that coats the foliage, grows black sooty mold, and draws ants, which then chase off the natural enemies that would otherwise keep whitefly in check. UC IPM notes outbreaks often begin exactly that way - when biological control gets disrupted - and that once populations are high the pest is genuinely hard to manage. Bemisia nymphs go further, causing distortion, discoloration, and the leaf silvering that gives silverleaf whitefly its name. Both species vector plant viruses. Indoors and under cover they are far worse than in the open garden, because it never gets cold enough to knock them back and their generation time collapses to about 18 days at 80-90°F. The single highest-value habit is inspecting every new plant, undersides included, before it enters the greenhouse or the garden.

Triggers: UC IPM: whiteflies become abundant in vegetable and ornamental plantings especially during warm weather, and outbreaks often occur when natural biological control is disrupted. Greenhouse whitefly develops egg to adult in as little as 18 days, with fastest development between 80 and 90°F, so populations compound quickly under cover or on overwintered indoor plants. They favor succulent, actively growing tissue. Host range is broad - UC IPM lists alfalfa, beans, cucumbers, eggplants, grapes, lettuce, melons, peas, peppers, potatoes, strawberries, tomatoes and many ornamentals. Ants tending the honeydew interfere with the natural enemies that would otherwise suppress them.

Risk fades when: UC IPM: abundant especially during warm weather. Development is fastest at 80-90°F, so protected culture and indoor overwintering sustain populations outside the normal outdoor season - which is exactly when houseplants and tender herbs brought inside get hit.

Leafminers are tiny fly larvae that feed between the upper and lower surfaces of leaves, creating winding pale tunnels or blotchy patches. They rarely kill plants but can ruin the marketability of leafy greens grown for foliage. Allium leafminer is an emerging pest in the eastern US (first detected in Pennsylvania in 2017) that damages onions, garlic, leeks, and chives.

Triggers: Liriomyza trifolii: 1 generation in ~1 month at typical greenhouse temps, 14 days at 95°F, 64 days at 59°F (UC IPM). Adults active mid-day. Allium leafminer emerges late March-early April, second flight September-October. Broad-spectrum insecticides trigger outbreaks by killing parasitoids.

Risk fades when: Parasitic wasps usually bring populations down as the season progresses unless broad-spectrum sprays disrupt them; damage peaks in warm spring and summer flushes and eases in cooler weather, so risk fades with natural-enemy buildup and falling temperatures (USU Extension, PNW Pest Handbook, UC IPM).