Sugar Ann Snap Pea

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.

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.

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.

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.

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).

The cowpea curculio is a small black weevil that has rendered cowpea production essentially unsustainable across much of the southeastern United States. Adults feed on and lay eggs in green pods; larvae develop inside, feeding on developing seeds, then drop to soil to pupate. Yield losses of 60% have been documented even with moderate infestations. The weevil has become resistant to standard pyrethroid insecticides.

Triggers: Overwinters as adult in soil/debris/weedy margins. Emerges April; feeds on weed hosts (cutleaf evening primrose, moss verbena, wild bean) until cowpeas mature May-June. Female chews hole in pod, lays egg inside. Larvae feed inside pod through 4 instars; drop to soil to pupate. Egg-to-adult 30-40 days. Two generations in AL/GA (May-June, August-September); one in VA.

Risk fades when: One generation in the mid-Atlantic with pressure concentrated in late spring and early summer, so risk drops after the first pod-set window passes; adults overwinter in field trash and nearby cover, and cleaning up crop debris after harvest reduces carryover (UGA Extension).

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 soil-borne vascular wilt that hits beans and peas through host-specific strains called formae speciales (basically subspecies that specialize in different hosts). Causes yellowing, stunting, wilting, brown streaks inside the stems, and long-term soil persistence — not splash-spread leaf spots.

Triggers: Warm soils, plant stress, soil compaction, and infested soil all favor the disease showing up. Wetness is a contributing stress factor, not the primary infection trigger.

Risk fades when: Weather pressure resolves slowly because soil-borne wilt doesn't disappear once symptoms start. A dry, stable week only lowers stress-driven expression — the pathogen stays in the soil.

Peas are a cool-season crop with a hard ceiling, and once they hit it the plant simply stops making a crop. USU Extension puts the first threshold at 80°F: pea flowers are very sensitive to temperatures above 80°F, and if dry conditions occur alongside the heat, the plants shed their flowers. UMN Extension gives the second: above 85°F peas stop growing and produce neither flowers nor pods, and hot day and night temperatures together cause flowers to abort. This is not a disease and there is nothing to treat. It is a calendar problem. Clemson notes the peculiar asymmetry that makes it worse - the plants tolerate frost and light freezes, but the blossoms do not. So peas must be sown as early as the ground can be worked, flower in the cool, and finish before summer arrives. Sow them late and the plants reach peak flowering exactly as the heat lands, and production shuts down. Heat also degrades what you do get: USU notes that stringy peas are further evidence of heat or water stress, as fibres in the pods toughen. Even Wando, bred specifically for heat tolerance, only shifts the ceiling - it does not remove it.

Triggers: USU Extension (peer-reviewed fact sheet): pea flowers are very sensitive to temperatures above 80°F, and if dry conditions occur the plants will shed their flowers; keep soil moist and mulch later plantings to minimise these stresses; stringy peas are further evidence of heat or water stress, as fibres in the pods toughen and the pods become less palatable. UMN Extension: peas need about 60 days of growth before harvest but will stop growing and produce no flowers or pods once temperatures get above 85°F, as often happens in June; hot day and night temperatures can cause flowers to abort, reducing yield; peas produced in hot weather may also have poor quality. Clemson HGIC: garden peas are cool-weather plants that withstand frosts and light freezes, although the blossoms cannot; the plants suffer in the heat and humidity of summer. Illinois Extension: peas may be planted whenever soil temperature is at least 45°F; early plantings normally produce larger yields than later plantings. Peer-reviewed work on field pea reports production declining when maximum day temperature during flowering exceeds about 77°F, with seed yield reductions of 24 to 60 percent under heat stress. Wando is bred for heat tolerance and shifts this ceiling upward, but does not remove it.

On Sugar Ann Pea: Warm weather quickly shortens flowering and pod fill in peas.

Prevention: Plant early and keep roots cool with mulch.

Risk fades when: There is no treatment. Flowers already shed do not return, and a plant that has shut down in July will not restart usefully as autumn cools - it has usually exhausted itself. Everything is decided at sowing. Plant as soon as the soil is workable and at least 45°F, choose shorter-maturity varieties where spring turns quickly to summer, and count backward: peas need roughly 60 days to harvest, and they must have flowered before daytime highs settle above 80°F. Mulch to keep roots cool and soil moisture even, since drought compounds heat and triggers flower shedding on its own. In hot regions a heat-tolerant variety such as Wando buys time. Clemson does not recommend fall plantings; Illinois allows midsummer sowings of heat-tolerant types to mature in cool autumn weather.

The Mexican bean beetle is one of the most serious legume pests in the eastern United States. It looks like a coppery-yellow ladybug with 16 black spots but, unlike beneficial lady beetles, feeds on bean foliage from the underside. Damage creates a characteristic 'lacework' or skeletonized appearance, often turning entire plantings brown.

Triggers: Overwinters as adult in leaf litter/field margins. Emerges spring, females lay yellow egg masses (40-75) on leaf undersides. 4 larval instars. One generation in north; 2-3 in south. Peak July-August.

Risk fades when: One to three generations run from June into early fall; the beetle overwinters only as an adult in sheltered debris, so frost ends the active population, and destroying spent bean plants right after harvest denies the last generation its food and cover (UMass Extension, CT Ag Experiment Station).

Poor fruit set means flowers appear normal but never produce fruit — they yellow, dry up, and drop. Most often this is heat-related pollen failure: day temperatures above 90°F, night temperatures above 75°F, or relative humidity above 80% all prevent pollen from being viable or released properly. Bean, tomato, pepper, squash, and cucurbit crops all experience it. For insect-pollinated crops (squash, cucumber, melon, watermelon), insufficient bee activity during flowering compounds the problem. Some crops recover with cooler weather and produce normally in late summer; others permanently lose a flush. Plant heat-tolerant varieties for hot-summer locations and time spring sowings to flower before the worst heat.

Triggers: Per UDel/UMD/UIllinois Extension: day temps >90°F + night temps >75°F + RH >80% during flowering all reduce pollen viability. Tomato extreme threshold: day >95°F / night >80°F causes complete pollination failure. Bean threshold: night >68°F (snap) / >70°F (lima) reduces set. Cucurbits also need adequate bee activity — heat reduces both pollen viability AND bee foraging.

Risk fades when: Most warm-season crops resume fruit set within 1-2 weeks of cooler weather. Bean and pepper plants typically catch up on harvest in late summer when temperatures moderate. Lost flush isn't recovered but later flowering is normal.

Pod set failure in legumes is almost always a nighttime heat problem. Snap bean pollen becomes nonviable when night temperatures stay above 68°F; lima beans fail above 70°F. Pollen quality drops, fertilization is incomplete, and the plant either drops the flower or sets a short twisted lumpy pod with few seeds inside. Daytime heat above 95°F adds to the problem but nights are the dominant factor. Peas behave similarly but earlier in the season — pea pod set fails when daytime temperatures climb above 80°F. Plants typically resume normal pod production once cooler weather returns; lost flush isn't recovered but later sets are normal. Plant heat-tolerant varieties (Annihilator, Jaguar, Dominator for snap beans) for mid-summer plantings and time spring sowings to flower before peak heat.

Triggers: Per UC ANR/UDel Extension: snap beans fail pod set when night temps >68°F sustained, lima beans >70°F. Day temps >95°F compound the problem but nights are dominant. Peas fail when day temps >80°F. Moisture stress at bloom compounds heat damage. Some varieties (Annihilator, Jaguar, Dominator for snaps; Cypress, Big Mama for limas) are screened for heat tolerance and produce better through summer heat waves.

Risk fades when: Bean plants typically resume normal pod set within 1-2 weeks of cooler nights. Lost flowers don't recover but new flowers form and set normally. Maintain consistent watering through heat — moisture-stressed plants suffer worse pod set.