Royal Carpet Alyssum Flowers

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).

Spider mites are tiny arachnids (1/50 inch) that feed on the undersides of leaves, producing characteristic silver-yellow stippling. Heavy populations produce visible webbing that interferes with pesticide coverage. They thrive in hot dry weather and drought-stressed plants. The two-spotted spider mite feeds on more than 180 cultivated plant species.

Triggers: Hot dry conditions; >90°F lifecycle <2 weeks. Drought stress amplifies. Broad-spectrum sprays (carbaryl, pyrethroids) trigger outbreaks by killing predators. Wisconsin Ext: 'as little as a month without significant rain during the growing season can favor a mite outbreak.'

Risk fades when: Populations build in hot, dry weather and then crash in late summer and fall as predatory mites catch up, host foliage declines, and cooler, wetter weather and rain set in, so risk fades once the heat and drought break (UC IPM, Colorado State Extension).

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.

Wind-flop is what happens when storms knock down plants that were standing fine. Different from regular flopping (which is gradual under the plant's own weight) — wind-flop is sudden and often dramatic. Corn after a thunderstorm, Brussels sprouts after a windy week, sunflower heads bent over from a single gust. Plants with shallow root systems (recent transplants, plants in containers) and tall plants with weak base stems are most vulnerable. Plants partially lodged (leaning but not broken) often recover if the soil is firmed back around their base. Plants snapped at the stem are usually a loss. Prevention: stake tall plants from the start, hill up around corn and tall brassicas as they grow, plant windbreak rows of taller plants to break gusts, choose dwarf or short-stem varieties for windy locations.

Triggers: Sudden wind events overwhelm structural support. Saturated soil after rain compounds risk because root anchoring is weaker. Tall corn, Brussels sprouts, sunflowers most commonly affected.

Risk fades when: Re-stake leaning plants by gently lifting and firming soil. Plants with snapped stems below the lowest leaf node are a loss.

Some flowers are cool-weather plants that were never going to carry a border through August, and treating their midsummer collapse as a disease leads people to water and feed them to death. Sweet alyssum is the clearest case. Wisconsin Extension describes it exactly: like many brassicas, growth and flowering slow in hot weather, the plants look ragged through the heat of summer, but they revive with cooler temperatures and last well into the fall. The remedy is a haircut, not a rescue - light shearing, watering, and light fertilisation aid recovery, and the plants rebloom when nights cool. Lupines behave the same way for a different reason: NC State Extension notes they dislike heat and humidity, want light afternoon shade in hot-summer regions, and in the deep South are best grown as annuals because they simply will not persist. Mulch to keep the roots cool, and deadhead the spent spikes. One trap is worth naming. Wisconsin warns that overly fertile soil promotes foliage over flowers, and that alyssum which is too wet or too crowded rots. So the instinct to feed and water a struggling plant makes both problems worse. Shear it, keep it merely moist, and wait for the weather to change.

Triggers: Wisconsin Horticulture (UW-Madison Extension), sweet alyssum: like many brassicas, growth and flowering slows in hot weather; plants look ragged in the heat of summer but revive with cooler temperatures and last well into the fall; light shearing, watering and light fertilisation aid recovery. Overgrown or leggy plants, or those with more seedpods than flowers, can be sheared back to promote reflowering. Older clumps may split, flowering only on the outer edges. Do not fertilise heavily, as overly fertile soil promotes foliar growth over flower production; plants that are too wet or crowded may rot. NC State Extension (Lupinus): these plants appreciate light afternoon shade in hot summer areas and dislike the heat and humidity of the deep South, where they are best grown as annuals; mulch keeps roots cool, and deadheading spent flower spikes encourages additional bloom. Perennial lupines are short-lived even in suitable climates. NOTE ON EVIDENCE: candytuft (Iberis umbellata) is included on the strength of Wisconsin's family-level statement about brassicas and its identical cool-season habit; there is no extension source addressing Iberis specifically. Nodding catchfly (Silene pendula) is deliberately excluded - no gold-standard source was found for it.

On Royal Carpet Alyssum: Hot weather can cause legginess and a pause in bloom.

Prevention: Shear lightly, water evenly, and allow cooler weather to restart flowering.

Risk fades when: This is not a disease and the plant is not dying. Shear alyssum back by about a third to a half when it turns ragged or carries more seedpods than flowers; new growth and a fresh flush of bloom follow in a couple of weeks once temperatures ease, and the autumn display is often better than the spring one. Water enough to keep the soil evenly moist but no more - a sheared plant uses very little, and wet crowded growth rots. Fertilise lightly if at all, since rich soil pushes leaves at the expense of flowers. For lupines, mulch the root zone to keep it cool, give afternoon shade in hot regions, and deadhead spent spikes. Where summers are genuinely hot and humid, grow lupines as annuals from a fresh autumn or early spring sowing rather than expecting them to persist.

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).

Self-seeding (or volunteer reseeding) happens when a plant is allowed to flower, set seed, and drop those seeds in the garden. Many cool-season crops like cilantro, dill, fennel, arugula, lettuce, and many flowers (calendula, cosmos, sunflower, poppy, nigella) reseed reliably year after year — often more reliably than deliberate sowing. Hybrid varieties typically don't reseed true-to-type — the seedlings may show traits of the parent lines rather than the labeled hybrid. Open-pollinated and heirloom varieties reseed faithfully. If you don't want volunteers, remove flower heads before seed sets. If you want them, leave seed heads on through fall and they'll sprout when conditions are right next season.

Triggers: Self-seeding follows any time a plant flowers, sets seed, and is left in place long enough for seed to mature and drop. Open-pollinated varieties reseed true; hybrid varieties may not.

Risk fades when: Self-seeding isn't a problem per se — it's the plant doing what plants do. Manage by deciding whether you want volunteers next season.