Kentucky Wonder Pole Bean

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.

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

Covers both halo blight and common bacterial blight on beans. Look for water-soaked spots on leaves and pods with yellow or greenish halos. Spreads aggressively in rainy, windy weather and reduces both yield and quality.

Triggers: Rain, wind, splash irrigation, handling wet plants, contaminated seed, and infected plant debris all drive spread.

On Kentucky Wonder Pole Bean: Warm wet foliage and splashing water spread bacterial spots.

Prevention: Rotate crops, avoid working wet plants, and water at soil level.

Risk fades when: Bacterial spread is water-driven. Four dry days without splash events lowers immediate spread risk significantly.

An aphid-transmitted potyvirus and the most widespread virus of common beans. Causes mottled light and dark green leaves, leaf distortion, and reduced pod set. Some strains cause systemic necrosis (black death of stems and leaves) in susceptible varieties. The virus is also seed-transmitted — infected seed produces infected plants. Resistance (coded BCMV) is widely bred into modern bean varieties. Numerous strain variants exist (NY15, US1, others) with corresponding resistance genes (I gene, bc-1, bc-2, bc-3).

Triggers: Aphid-transmitted, also seed-borne. Active during warm aphid-favorable weather.

Risk fades when: Extreme heat reduces vector activity. Note: existing infections cannot be cured.

A beetle-transmitted virus of beans (primarily soybean but also snap and dry beans) spread mainly by bean leaf beetles. Causes mottled leaves and characteristic mottled or discolored pods that reduce marketability. The virus overwinters in beetles and weed hosts. Resistance is less developed than for BCMV — management focuses on beetle control and clean seed. Most commonly a concern in regions with established bean leaf beetle populations (Midwest and Mid-Atlantic).

Triggers: Bean leaf beetle-transmitted. Active when beetle populations are active (warm spring through summer).

Risk fades when: Extreme heat reduces vector activity. Note: existing infections cannot be cured.

A bean-specific rust producing reddish-brown powdery pustules on bean leaves, stems, and pods. Severe infections can defoliate plants.

Triggers: High humidity, prolonged leaf wetness or dew, and warm moist weather favor the spores (urediniospores) to germinate and form new pustules.

Risk fades when: Dry foliage and heat above the mild rust-favorable range reduce new infections.

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 4-6 hours of standing water on the plant tissue. UMN's data shows it's unlikely in open home gardens.

Risk fades when: Temperatures above 82°F suppress growth and spore production. That's the published threshold.

Different from cucurbit powdery mildew, this one mainly affects peas and some beans. It forms white powdery growth on leaves, stems, and pods — especially on late-planted or late-maturing legumes during warm, humid stretches.

Triggers: Warm temperatures, humid plant canopies, poor airflow, and late plantings all favor the disease. Rain isn't required and may even slow it down by knocking spores off.

Risk fades when: Activity drops when weather moves outside the warm, moderately humid range it likes. Hot spells above the favorable zone reduce new pressure.

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.

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).

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.

The sweetclover weevil is a small gray-brown weevil specializing on sweet clover (Melilotus spp.), with secondary feeding on alfalfa and ladino clover. Adults notch leaf edges; larvae feed on roots and nitrogen-fixing nodules. Most damage occurs on cotyledon-stage seedlings — established stands in the Canadian prairies typically tolerate populations without significant yield loss.

Triggers: Diapause as adult overwinter. Cultivar selection matters — Melilotus alba less preferred than M. officinalis; wild M. infesta least preferred (Soroka & Muir). Nitrate fertilizer levels don't affect feeding.

Risk fades when: Damage is concentrated on cotyledon-stage seedlings in spring; once plants grow past the seedling stage they outgrow the notching injury, so risk fades as the stand establishes, and adults move off to oversummer and overwinter in sheltered sites (Craig 1978).