Blue Curled Scotch Kale

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.

On Blue Curled Scotch Kale: Dense leaf growth and cool-to-mild weather allow aphid colonies to build on leaf undersides

Prevention: Maintain airflow, avoid excess nitrogen, wash colonies off early, and encourage beneficial insects

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.

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.

Where it lives: Across the US, including watered gardens in the desert Southwest

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.

Where it lives: Throughout the United States

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.

Where it lives: Across the US in summer; outdoors all year only where winters do not freeze

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.

Wireworms are the larvae of click beetles. They live in the soil, eating seeds, seedlings, roots and tubers, and they bore small holes and tunnels into potatoes and sweet potatoes that can make them unusable. For home-garden sweet potatoes, UGA Extension says wireworms and root-knot nematodes seem to be the biggest problems. Their main food is the roots of grasses, so the worst damage comes in gardens dug out of sod or lawn within the past few years. Some kinds take several years to grow up, so a problem bed can stay a problem for years. Severe outbreaks are rare, and once you see damage no spray will fix it: the steps that work are taken before planting.

Where it lives: Found across the US; different wireworm species are the main pests in different regions

Triggers: Larvae and adults spend the winter 9 to 24 inches deep in the soil. In spring, once the soil warms to about 50 F, larvae feed within the top 6 inches; when the soil gets too hot (above 80 F) or dry they go deeper, and as the soil cools in fall they may feed near the surface again. They like moist, cool, heavy soil. Female click beetles lay eggs in grassy, weedy areas, which is why ground that was sod or lawn has the most wireworms. How long one generation takes depends on the kind: from one to six years. The corn wireworm takes up to six years, so larvae of every size are in the soil at once. In the Southeast, the southern potato wireworm has one or two generations a year and the tobacco wireworm has one.

Risk fades when: Wireworms do most of their damage in early spring, when they are near the soil surface; in summer they move deeper, and as the soil cools they may feed near the surface again (NDSU Extension). They become active and look for food as soon as the soil warms in spring (UMass Extension). In the Southeast, wireworms usually attack potatoes and sweet potatoes late in the season (Clemson HGIC; NC State Extension). The month numbers are a reading of 'spring' and 'late season' for most of the US; spring comes earlier in the South and later in the North.

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.

Where it lives: Across the US; the allium leafminer only in the Northeast and Mid-Atlantic so far

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).