America Spinach

A virus spread by the beet leafhopper (Circulifer tenellus), mainly a problem in the western US — California, Arizona, Colorado, Idaho, New Mexico, Utah, and Washington. It has a broad host range, infecting beets, tomatoes, peppers, beans, and cucurbits. Infected plants develop curled, thickened leaves with purple-tinged veins on the undersides, stunted growth, and fruit that ripens prematurely. The leafhopper transmits the virus while migrating: it lands and briefly probes plants, and a single feeding of just a few seconds is enough to infect.

Where it lives: Western US, from the Great Plains to the Pacific

Triggers: Driven by leafhopper migration, not weather directly. The bugs overwinter in foothill weeds and head for gardens in late spring once the wild vegetation dries up. Hot, dry years push more of them into populated areas. Symptoms show up 7-14 days after a single leafhopper visit — and a single bite is all it takes.

Risk fades when: Migration peaks in late spring; once the main wave passes, transmission risk drops sharply. The virus doesn't hide in soil or plant debris between seasons, so risk resets each year.

Spinach is the most photoperiod-sensitive of the leafy greens — it bolts strongly when daylight exceeds 14 hours, almost regardless of temperature. Heat above 75°F accelerates the process. In zones 4a-7b, this means most spring spinach has 4-6 weeks of useful harvest before mid-to-late June. After bolting, leaves turn narrow and bitter quickly. Plant a long-day-resistant cultivar (Bloomsdale Long Standing, Tyee, Reflect) and time spring sowings to harvest before solstice. Fall plantings starting in August give a much longer harvest window because days shorten as the crop grows.

Triggers: Spinach is primarily a photoperiod responder, not a vernalization responder. Long days (>14 hours) trigger flowering on their own; heat above 75°F speeds it along. Bolts faster than lettuce in identical conditions.

On America Spinach: Long days plus rising temperatures push spinach into flower stalk formation and make leaves smaller and less sweet

Prevention: Direct sow very early or for fall, keep moisture even, use row cover for cold rather than late spring heat, and choose slower-bolting cultivars for warmer slots

Risk fades when: Bolted spinach is done. Fall sowing from mid-August onward gives a longer harvest window because daylight is shortening rather than lengthening as the crop grows.

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.

Where it lives: Across the US except Alaska; moths fly north from the South each summer

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 widespread and destructive spinach disease there is, and it only attacks spinach. Dull to bright yellow spots appear on the upper leaf surface, and directly beneath them a purplish-gray fuzzy growth develops on the underside - that fuzz is the diagnosis. It forms overnight and the spores blow away during the day, so early morning is the time to look. Older leaves are hit first. With time the spots enlarge, turn tan, and dry out; heavily infected leaves curl, distort, and look blighted. Free moisture on the leaf is required for the spores to germinate, which is why dense plantings that never dry out and overhead sprinklers are the classic setup for an outbreak. The pathogen exists as many distinct races and keeps adapting to new cultivars, so resistant varieties are the single most effective control - but check which races a variety resists. Dry, warm, breezy weather shuts it down. Because it infects nothing else in the garden, a one-year break from spinach in that bed measurably lowers disease pressure.

Triggers: Per UC IPM: free moisture on the leaf is necessary for spore germination and infection, though the pathogen does not need moisture to keep growing once inside the leaf. Spores form only in darkness or subdued light under a near-saturated atmosphere, then disperse by wind and splashing water; in cool moist conditions they survive several days. The dense canopy of closely-sown spinach traps moisture and creates ideal infection conditions. Dry, desiccating winds and clear, warm days inhibit spread. Cornell notes the pathogen can also be seedborne as oospores. The pathogen exists as distinct genetic races that adapt to new cultivars.

What it looks like: Dull to bright yellow spots on spinach seed leaves and on leaves of every age, often with purple growth on the underside beneath them. The spots enlarge, turn tan and dry, and heavy infection curls and distorts the leaves until they look blighted.

Disease or overwatering? Turn a spotted spinach leaf over. Purple growth underneath a yellow spot points to downy mildew. Spinach limp and pale from soggy soil has no spots and no growth underneath. It spreads in cool, wet weather and in thick plantings that hold moisture.

Will it recover? Spotted spinach leaves turn tan and dry and do not recover. Next time, grow a resistant spinach variety, the most effective control, and avoid crowding plants; the disease keeps forming new races that can beat older resistant varieties.

On America Spinach: Cool, wet foliage and dense canopies favor infection and leaf spotting

Prevention: Water at soil level, thin for airflow, rotate crops, and harvest promptly in wet weather

Risk fades when: UC IPM: dry, desiccating winds and clear, warm days inhibit the growth and spread of downy mildew. Three dry days with highs above 70°F exits the active infection window. Leaves already infected stay damaged and will not recover.

Source for the signs above: UC IPM Pest Management Guidelines: Spinach, Downy Mildew

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.

What it looks like: On lettuce close to harvest, a brown, soft rot eats into the crown where stems and leaves touch the soil. The older leaves wilt first, then the whole head wilts and collapses. Heavy white mold and small, hard, black resting bodies, up to about 1/8 inch, form on the outside of the rotted crown.

Disease or overwatering? Check the base of a collapsed lettuce. Thick white mold and small hard black bodies on a soft brown crown point to lettuce drop. Lettuce that sags in soggy soil has a firm crown with no mold. Botrytis crown rot and Verticillium wilt can look similar, so the white mold with black bodies is the deciding sign.

Will it recover? A collapsed lettuce cannot be harvested and will not recover. Pull infected plants and take them away; the black resting bodies survive in soil for 2 to 3 years. Next time, keep the bed surface as dry as you can, make sure it drains, and avoid following beans, cauliflower, celery, endive, pepper or tomato.

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.

Source for the signs above: UC IPM Pest Management Guidelines: Lettuce, Lettuce Drop

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.

Where it lives: Throughout the United States

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.

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

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.

Where it lives: Across the US

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 5-8 hours of standing water on the plant tissue. UMN's data shows it's unlikely in open home gardens.

What it looks like: On lettuce, a soft, wet, brownish-gray to brownish-orange rot starts on the oldest leaves lying on the soil, then moves into the crown. Fuzzy gray to brown mold covers the rotted base where it is shaded by the leaves above, and flat black resting bodies can form. Badly hit plants wilt and collapse.

Disease or overwatering? Look under the outer lettuce leaves at the crown. A soft, wet rot covered in gray to brown fuzz points to gray mold. Lettuce that sags from soggy soil has no fuzz and no rotted crown. The wilt and collapse alone can look like lettuce drop, so the gray to brown fuzz is the sign to go by.

Will it recover? A lettuce crown that has rotted through will not recover; the plant wilts and collapses. Pull it. Next time, avoid bruising or breaking leaves, keep the bed surface from staying wet for long stretches, and do not set out overgrown transplants, which break and get infected more easily.

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

Source for the signs above: UC IPM Pest Management Guidelines: Lettuce, Botrytis Crown Rot (Gray Mold)

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.