Chervil

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.

On Chervil: Soggy dense seedbeds can kill small seedlings.

Prevention: Use well-drained soil and avoid overwatering during emergence.

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.

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.

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 Chervil: Tender tips can attract sap-feeding pests.

Prevention: Encourage beneficial insects and rinse light infestations away.

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

Dill has a short leafy window and then it runs. It is a cool-season annual, and USU Extension names the two things that shorten that window: temperature stress from high heat, and overcrowding. Once the flower stalk rises, the plant redirects everything into seed, the feathery fronds thin out and sharpen in flavour, and the leaf harvest is effectively over. Dill germinates in one to three weeks and gives leaves about six to eight weeks after sowing, so the arithmetic is unforgiving in a hot summer. The honest answer is that you cannot stop a dill plant from bolting - you can only make sure another one is coming along behind it. USU's prescription is thinning and succession planting, and that is the whole strategy: sow a short row every two to three weeks, thin properly so plants are not crowded, sow in the cool halves of the season, and give afternoon shade where summers are hot. Do not pull a bolted plant straight away. The flowers feed pollinators, the seed is worth harvesting for the kitchen, and dill is a host plant for swallowtail caterpillars.

Triggers: USU Extension (dill, peer-reviewed fact sheet): germination in 7 to 21 days, harvest generally 6 to 8 weeks after sowing; temperature stress (high heat) and overcrowding promote bolting, and thinning seedlings plus succession planting helps. UMN Extension (growing herbs): for carrot-family herbs, flowering signals the end of the plant's life, and herbs have the best flavour if harvested just before flowering. NOTE ON EVIDENCE: chervil (Anthriscus cerefolium) is included here on the basis that it is an apiaceae cool-season annual with the same habit and the same remedy - sow in cool seasons, provide partial shade, resow every three to four weeks. Extension coverage of chervil specifically is thin; the dill thresholds should be treated as indicative for it rather than measured.

On Chervil: Warm weather triggers fast flowering and shortens the leaf window.

Prevention: Grow in cool seasons, provide partial shade, and resow every 3-4 weeks.

Risk fades when: A bolted dill plant does not return to leaf. Accept it and plan around it: sow a short row every two to three weeks through spring and again in late summer, thin seedlings to proper spacing so crowding does not hurry them along, and site plants where they get afternoon shade in hot regions. Skip midsummer sowings in hot zones entirely. Keep soil evenly moist, since drought stress accelerates flowering. Once a plant has bolted, leave it standing: the umbels feed hoverflies and parasitic wasps, the seed is a spice in its own right, and dill is a larval host for black swallowtail butterflies.

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.

Covers parsley, dill, cilantro, lovage, and angelica leaf-spot pressure from host-family fungi — especially Septoria on parsley and cilantro. Causes small tan to brown leaf spots, yellowing, and defoliation during wet, humid, splashy weather.

Triggers: Wind-driven rain, dew drips, overhead irrigation, tools, handling wet plants, infected debris, and seedborne inoculum all drive spread.

Risk fades when: Spread depends on wet foliage, splash, dew, and wet-plant handling. A dry period lowers immediate new infection risk.

A powdery mildew of carrot-family herbs such as dill, parsley, fennel, and cilantro. It coats leaves and stems with a white-to-gray powdery growth, and heavy infection yellows and weakens foliage and taints flavor. Unlike most leaf diseases it spreads in warm, dry weather with high humidity, and does not need leaf wetness.

Triggers: Powdery mildew thrives in warm, humid conditions and, unlike most fungi, does not require leaf wetness; rain actually suppresses it. Shade and crowding raise risk.

Risk fades when: Sustained heat above about 90°F slows powdery mildew. Two such days reduces active pressure; existing colonies remain on infected leaves.

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).