Shungiku (Edible Chrysanthemum)

Lettuce bolting is the plant shifting from leaf production to flower/seed production — and it's mostly triggered by photoperiod (day length), not heat. MSU research shows: cold weather during seedling growth followed by long summer days (14+ hours of daylight) is the strongest trigger. Heat above 80°F speeds it along once it starts, but day length is the primary cue. Once a central stalk emerges and the plant commits to flowering, leaves turn bitter within 3-5 days from chemicals called sesquiterpene lactones. There's no way to reverse it. Plant slow-bolt cultivars, time spring sowings to avoid late-cold + early-long-day overlap, and harvest cut-and-come-again style to extend the window.

Triggers: Per MSU Extension, the real trigger is cold spring growth (vernalization) followed by long summer days (>14 hours), not heat alone. Above 68°F the plant 'devernalizes' (reverses progress toward flowering) which is why fall-sown lettuce bolts less. Heat above 80°F accelerates once flowering starts but isn't the primary cue. Drought stress and pest pressure can also accelerate.

On Shungiku: Warm weather and long days push rapid flowering

Prevention: Grow in spring and fall and harvest before stems elongate

Risk fades when: Bolting is irreversible once the central stalk emerges. The plant is done as a salad crop. Pull it, save seed if it's an open-pollinated variety you like, or compost. Plant fresh seed for fall harvest after midsummer when nights lengthen again — fall lettuce rarely bolts.

Corn earworm is the same species as tomato fruitworm and cotton bollworm — a polyphagous caterpillar that bores into ears of corn through fresh silks, into tomato and pepper fruit, into lettuce heads, and into bean and pea pods. In sweet corn, losses can reach 50%. The species migrates north annually from southern overwintering grounds; in much of the northern US, it does not survive the winter when temperatures drop below 30°F.

Triggers: Overwinters as pupa in top 2-4 inches of soil where winter temps permit. North of I-70 (Illinois IPM): does not reliably overwinter — populations arrive via migration mid-July through September. Females prefer fresh corn silks for egg-laying; older silks rejected.

Risk fades when: In the North (above roughly 40 degrees latitude) the insect does not overwinter, so populations arrive only by summer migration and are wiped out by fall frost, resetting each year; in the South it overwinters as a soil pupa and pressure lasts longer (UMN VegEdge, Wisconsin Hort, Cornell IPM).

A seedling killer caused by several different fungi working together. It hits vegetables, flowers, herbs, microgreens, and cover-crop seedlings the same way — seeds rot before they emerge, or young seedlings collapse right at the soil line. Wet seed-starting mix and poor airflow in seedling trays are the classic conditions.

Triggers: Wet soil or starting mix, poor drainage, seedlings packed too tightly, contaminated trays or media, and stagnant air all favor damping-off.

Risk fades when: Drying the soil surface and improving airflow slows new spread. Collapsed seedlings don't recover, but the rest of the tray can be saved.

The most common and damaging foliar disease of lettuce. It causes light green to yellow angular patches on the upper leaf surface, bounded by the veins, with a white fluffy growth on the underside. Older, outer leaves are hit first, and severe infections make heads unmarketable. It spreads in cool, damp weather with prolonged leaf wetness.

Triggers: Cool, moist conditions with leaf wetness are required for infection. Spores are short-lived and dispersed by wind during moist periods. Most active at 50-64°F; activity falls off above about 70°F.

Risk fades when: Warm, dry weather suppresses the pathogen. Three dry days with highs above 70°F exits the active infection window, though infected leaves stay damaged.

A soilborne rot that attacks the crown and lower leaves where they touch the ground. Infected tissue turns into a brown, soft decay, the outer leaves wilt, and eventually the whole plant collapses, usually near maturity. White cottony growth and small hard black resting bodies form on the rotted crown. Wet soil and cool, moist conditions drive it.

Triggers: Wet soil conditions favor both Sclerotinia species. Cool, moist weather is needed for S. sclerotiorum to produce its airborne spores; S. minor infects crown and lower leaves in contact with the soil. Sclerotia survive in soil for 2 to 3 years.

Risk fades when: Drying soil slows new infection. Five dry days exits the active window, though established crown rot does not reverse and sclerotia persist in soil.

Tipburn looks like a disease but it's the same mechanism as tomato blossom-end rot — calcium can't reach the fast-growing inner leaves of the lettuce head, the cells collapse at the margins, and brown necrotic patches appear. Most commonly triggered by a drought-then-rain cycle: the plant grows slowly when dry, then growth explodes when water returns and the new leaf cells outpace the calcium supply. Heat and rapid nitrogen-fed growth make it worse. Closed-head varieties (iceberg, butterhead) hide tipburn inside the head until cut open — by then it's too late. Open-leaf and loose-leaf lettuces show it earlier on outer leaves and can sometimes be trimmed. Foliar calcium sprays don't fix it because calcium can't move through phloem to inner tissue; the only prevention is steady soil moisture + slower growth.

Triggers: Per UC IPM and Cornell Vegetable Program: tipburn results from calcium-transport failure in expanding inner leaves. Triggers: drought-then-rain swings (USU), high humidity reducing transpiration (Cornell), excess nitrogen pushing rapid growth, soil pH outside 6.0-6.8. Closed-head varieties hide tipburn inside until harvest; open-leaf shows it earlier.

Risk fades when: Foliar calcium sprays don't reach inner head leaves and won't reverse damage already done. Once tipburn shows, the head is compromised — trim outer leaves on open types or harvest early. Prevent next planting via consistent moisture, lower-nitrogen fertilization, and avoiding mid-summer heat-stressed crops.

Aphids are soft-bodied sap-sucking insects that cluster on tender new growth. Most established plants tolerate moderate populations and will outgrow damage on their own, but aphids are the most important plant virus vectors in the garden, transmitting more than 100 plant viruses including potato leafroll, cucumber mosaic, and turnip mosaic. Honeydew excreted while feeding supports sooty mold growth and attracts ants that protect aphids from natural enemies.

Triggers: Optimal development at ~75°F (green peach aphid) per UC IPM Floriculture; melon aphid develops fastest above 75°F. Many species heat-intolerant above 90°F and crash in mid-summer. Soft new growth and over-fertilization with high N favor population buildup. Females give live birth parthenogenetically most of growing season — one generation in ~1 week under optimal conditions.

On Shungiku: Tender new growth attracts sap feeders

Prevention: Wash off early colonies and avoid excess nitrogen

Risk fades when: Per UC IPM and Clemson HGIC, populations crash in mid-summer heat (>90°F) for many species, return in cooler conditions

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.

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.

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.