Tansy

A soil-borne fungus (*Sclerotium rolfsii*) that attacks plant stems right at the soil line during hot weather. It hits over 500 different plant species. Two telltale signs to look for: white fan-shaped fungal growth on the lower stem, mulch, and soil surface, and tan-brown spherical sclerotia (they look like mustard seeds) on infected tissue. Most active during sustained heat with humid conditions.

Triggers: Optimal at 86°F (30°C) soil and air temperature with humid conditions. Inactive below 70°F. Most damaging during sustained mid- to late-summer heat waves. It extends further north in warmer-than-normal seasons.

Risk fades when: Sustained cooler weather — highs below 80°F and overnight lows below 70°F for 5+ days — reduces fungal activity. The sclerotia (resting bodies) persist in soil for years, so resolution is seasonal, not curative.

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.

A water mold (not a true fungus) that attacks roots and crowns in waterlogged soil. It's most dangerous in heavy, poorly drained soil after extended rain — basically any time water sits around plant roots for days.

Triggers: Pythium infects from 50-95°F as long as the soil stays saturated. Phytophthora capsici is most active at 75-85°F. What matters most is how long the soil stays waterlogged, not just whether it rained.

On Tansy: Poor drainage in winter-wet sites

Prevention: Choose well-drained soil and avoid overwatering

Risk fades when: Risk fades when soil returns to field capacity (normal drained moisture). How long that takes depends on your soil — sand drains in hours, clay can take days.

These plants spread two ways at once, and controlling only one of them is why gardeners lose. Above ground they self-seed prolifically. Below ground they run - by rhizomes in tansy, mugwort and soapwort, by stolons in evening primrose - throwing up new shoots several feet from the parent. The underground half is the dangerous half, and it turns the obvious remedies into mistakes. UMD Extension's instruction for mugwort is four words long: never till it. Each root piece will generate a new plant, and research puts the regenerating fragment size at about two centimetres. So rototilling an infested bed does not remove the plant, it propagates it - chopping the rhizomes into cuttings and distributing them evenly. Hand pulling has the same flaw at smaller scale, snapping the rhizome and leaving the rest behind. NC State does not mince words about tansy either: it spreads rapidly by rhizomes and prolific seed, it is a listed noxious weed in many states, and it is not recommended for beds or borders. What works is smothering, exhausting, containing, and cutting the seed off before it ripens - and, above all, getting to young plants before they form rhizomes at all.

Triggers: UMD Extension (mugwort): spreads by extensive rhizomes; never till it, because each root piece will generate a new plant; smother with black plastic or layers of newspaper covered with mulch, or exhaust the root system by continuous removal of leaves. NC State Extension (mugwort): an aggressive perennial spreading by persistent rhizomes; it can reproduce from small fragments of the rhizomes, so hand removal is difficult; it is spread by cultivation, thrives in mulched landscape beds, and most infestations begin with contaminated root balls of nursery plants or with movement of contaminated soil. Research cited by state invasive-species programs finds mugwort regenerating from rhizome fragments as small as about 2 cm; mugwort is also allelopathic. Cornell Cooperative Extension: a single mugwort plant can produce up to 200,000 seeds, though seed is not considered the main contributor to spread. UConn IPM: hand pull very young plants in spring or early summer, before rhizomes form; mow before seedheads mature; stabilise and reseed bare ground, since seeds sprout wherever bare soil is exposed. NC State Extension (common tansy): spreads rapidly by its rhizomatous root system and prolific seed production; reproduces by seeds, rhizomes and root fragments; listed as a noxious weed in many areas of the United States; not recommended for flower beds or borders; deadhead or shear off blooms to control self-seeding. Tansy contains thujone, which may cause skin irritation or contact dermatitis - wear gloves when handling. Evening primrose spreads by stolons and self-seeding; soapwort by rhizomes and self-seeding.

On Tansy: Self-seeding and rhizomatous clump expansion

Prevention: Deadhead spent flowers and divide or contain clumps regularly

Risk fades when: Do not till, and do not rototill an infested bed - cultivation chops rhizomes into fragments and spreads them. Pulling snaps the rhizome and leaves the rest to resprout, so it works only on very young plants that have not yet formed rhizomes; scout and remove those promptly. For established patches, smother with black plastic or thick layers of newspaper under mulch, or exhaust the roots by removing every leaf, repeatedly, over a long period. Combine methods. Contain deliberate plantings with a physical root barrier or grow them in containers. Cut the flowers off before seed ripens - mowing or shearing before seedheads mature prevents the seed half of the problem entirely. Keep bare soil covered, since seed germinates on exposed ground. Buy plants carefully: mugwort infestations often arrive in the root ball of nursery stock. And wear gloves with tansy, whose thujone can cause contact dermatitis.

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.

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

Flopping happens when stem strength can't support the plant's mass — usually because the plant grew too fast, didn't get enough sun to build strong stems, or got too much nitrogen which pushes soft leafy growth at the expense of structural strength. Rain and wind compound the problem by weighing down soft tissue. Some plants are inherently floppy — peony, dahlia, delphinium, large mum, tall sunflower — and need staking from the start. Others normally hold themselves up but flop when grown in shade or overfed. Stake early (in spring before plants have grown into their support) rather than late (when stems are already bent and a stake just preserves the deformity). Pruning or pinching tall plants when young encourages branching and reduces flop risk.

Triggers: Per MSU Extension: full sun produces sturdy self-supporting plants; shade or over-fertilization produces soft top-heavy growth. Rain and wind accelerate flop. Plants with naturally heavy blooms (peony, dahlia, large lily, hollyhock) need staking from start.

Risk fades when: Stake early in spring before too much growth. Late staking just preserves the bend. Pinch tall plants when young to encourage branching. Reduce nitrogen feeding if plants are floppy and overgrown.

A powdery mildew specific to the sunflower family — distinct from cucurbit, legume, brassica, and Ribes powdery mildews. Affects sunflowers, zinnias, asters, cosmos, marigolds, coneflowers, daisies, gaillardia, tickseed, and related ornamentals.

Triggers: Asteraceae powdery mildews are favored by warm days, high humidity, shaded or dense canopies, and dry leaf surfaces — they prefer humid air over standing water.

On Tansy: Humid crowded growth late in the season

Prevention: Space plants well and prune for airflow

Risk fades when: Hot weather above the typical powdery-mildew favorable range lowers new pressure.

Premature dieback covers a range of end-of-season behaviors. Annual herbs (basil, cilantro, dill) decline naturally as days shorten and temperatures cool — this is normal once flowering has happened. Tender perennials in cold climates may die back to the ground when frost arrives. But premature dieback before its time can signal: cold snap below the plant's tolerance, root disease (Fusarium, Verticillium, Pythium), pest pressure (root-feeding larvae), or simply the plant having reached the natural end of its cycle. Annual basil typically dies after first frost; if basil dies in mid-summer, that's a sign to investigate. Tender perennial herbs in zone 5-6 die back annually and regrow from roots — that's normal. Distinguishing 'natural cycle complete' from 'plant has a problem' is about timing and visible symptoms.

Triggers: Most herb dieback is natural end-of-season. Mid-season dieback usually indicates root disease, pest damage, or severe drought stress. Investigate visible signs before assuming normal cycle.

Risk fades when: Natural dieback of annual herbs at season end is expected. Mid-season dieback warrants investigation: dig up the plant, check roots for rot/galls, examine stems for borer damage.

Scales are immobile sap-sucking insects under protective waxy or hardened covers. Soft scales produce sticky honeydew that supports sooty mold; armored scales cause direct dieback. They are primarily pests of woody plants and perennial herbs — fruit trees, berries, citrus, bay, rosemary — rather than annual vegetables. Females are sedentary as adults; the mobile 'crawler' stage that hatches in late spring/early summer is the target for control.

Triggers: Most species: one generation/year in north; multiple in south. Lecanium overwinters as 2nd-instar nymphs on twigs; crawlers emerge June-July. San Jose scale overwinters as 2nd instar on bark; crawlers May-June. Stressed plants more susceptible; ant attendance protects scales by deterring parasitic wasps.

Risk fades when: The vulnerable stage is the mobile crawler, which appears in a narrow late-spring to early-summer window depending on species; once crawlers settle and form their protective covering, sprays are far less effective, so the treatable risk window closes after crawler emergence (Penn State Extension, UMN Extension).

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).