Field-ready summary of the seven pest and disease pressures BAU's Pest Watch tool tracks: crops affected, weather conditions that trigger risk, and first-response actions for Zone 7–9 growers.

Most specialty-crop losses in USDA Zones 7–9 don't come from surprise pests — they come from weather windows that predictably favor a pathogen or insect the grower already knows about. Late blight, downy mildew, and bacterial spot each have a temperature-and-moisture fingerprint. If you can read the forecast against that fingerprint, you can spray before infection, not after.

This guide summarizes the seven pest and disease pressures BAU's Pest Watch tool watches for automatically — what triggers each, which crops are at risk, and the first action to take.

The seven risks we track

Late blight (Phytophthora infestans)

Crops affected:: Tomato, potato
Weather trigger:: 2+ consecutive days with lows 50–80°F and ≥10 hours of leaf wetness (RH ≥ 90%).
First action:: Scout lower leaves daily. Apply preventive copper or chlorothalonil before the next wet window — curative sprays rarely catch it.

Early blight & Septoria leaf spot

Crops affected:: Tomato, pepper, eggplant
Weather trigger:: 2+ warm wet days (75–90°F highs) with leaf wetness and ≥0.1″ rainfall.
First action:: Mulch to block soil splash, prune lower foliage for airflow, rotate fungicides (mancozeb / chlorothalonil) on a 7–10 day schedule.

Cucurbit downy mildew

Crops affected:: Cucumber, melon, watermelon, squash, pumpkin
Weather trigger:: Cool nights (lows 50–70°F) with 6+ hours of leaf wetness for 2+ consecutive days.
First action:: Check the ipmPIPE cucurbit downy mildew forecast. Apply preventive mefenoxam or oxathiapiprolin and open canopy for airflow.

Powdery mildew

Crops affected:: Cucurbits, peppers, tomatoes
Weather trigger:: 3+ days with highs 68–88°F, humidity ≥ 70%, and no washing rainfall (<0.1″).
First action:: Apply potassium bicarbonate, sulfur (skip if temps >90°F), or a labeled biofungicide. Thin canopy so leaves dry by midday.

Bacterial spot & speck

Crops affected:: Tomato, pepper
Weather trigger:: 2+ warm days (highs ≥ 75°F) with heavy rainfall (≥0.3″) — splash disperses bacteria.
First action:: Apply a fixed copper + mancozeb tank mix. Do not work fields when foliage is wet — hands and equipment spread it plant to plant.

Heat stress (pollen sterility, blossom drop)

Crops affected:: Tomato, pepper, bean, cucurbits, brassicas, greens
Weather trigger:: 2+ consecutive days with highs ≥ 95°F.
First action:: Irrigate early morning, apply 30% shade cloth on tender crops, and harvest greens before the afternoon peak.

Aphid & thrips pressure

Crops affected:: Greens, brassicas, solanaceae, cucurbits, beans
Weather trigger:: 4+ mild dry days (highs 65–82°F, no rainfall) — no rain to knock populations back.
First action:: Scout leaf undersides. Release lacewings or apply insecticidal soap once thresholds are exceeded; rotate modes of action to slow resistance.

Crop-specific checklists

Use these quick-reference checklists during weekly walk-throughs. Each row pairs a weather trigger with the first action to take — designed to be scannable on your phone in the field.

Tomato

Risk	Weather trigger	First action
Late blight	2+ days, lows 50–80°F + ≥10 hrs leaf wetness (RH ≥ 90%).	Preventive copper or chlorothalonil before the next wet window.
Early blight / Septoria	2+ warm wet days (75–90°F) with ≥0.1″ rain.	Mulch to block soil splash, prune lower leaves, rotate mancozeb/chlorothalonil on 7–10 day schedule.
Bacterial spot & speck	Warm days (≥75°F) with heavy rain (≥0.3″).	Fixed copper + mancozeb; never work wet foliage.
Powdery mildew	3+ days, 68–88°F, RH ≥ 70%, <0.1″ rain.	Potassium bicarbonate or sulfur (skip >90°F); thin canopy.
Heat stress / blossom drop	2+ days with highs ≥ 95°F.	Early-morning irrigation; 30% shade cloth over flowering plants.

Pepper

Risk	Weather trigger	First action
Bacterial spot	Warm days (≥75°F) with heavy rain (≥0.3″).	Fixed copper + mancozeb; stay out of wet fields.
Early blight / Septoria	2+ warm wet days with leaf wetness.	Prune for airflow, mulch, rotate protectant fungicides.
Powdery mildew	3+ days, 68–88°F, RH ≥ 70%, dry.	Potassium bicarbonate or biofungicide; open canopy.
Heat stress / pollen sterility	2+ days ≥ 95°F.	Shade cloth, deep morning irrigation; expect flower drop.
Aphids & thrips (TSWV vector)	4+ mild dry days, 65–82°F.	Scout undersides; insecticidal soap or spinosad, rotate modes.

Eggplant

Risk	Weather trigger	First action
Early blight / Phomopsis	2+ warm wet days (75–90°F) with leaf wetness.	Rotate mancozeb/chlorothalonil; remove infected fruit promptly.
Bacterial spot	Warm days ≥ 75°F with heavy rain.	Fixed copper; avoid overhead irrigation.
Flea beetles	4+ mild dry days after transplant.	Row cover until flowering; spinosad or pyrethrin at threshold.
Aphids & thrips	4+ mild dry days, 65–82°F, no rain.	Insecticidal soap; release lacewings; rotate MoA.

Cucurbits (cucumber, melon, squash, pumpkin)

Risk	Weather trigger	First action
Cucurbit downy mildew	Lows 50–70°F with 6+ hrs leaf wetness for 2+ days.	Check ipmPIPE forecast; preventive mefenoxam or oxathiapiprolin.
Powdery mildew	3+ days, 68–88°F, RH ≥ 70%, dry.	Potassium bicarbonate/sulfur (skip >90°F); thin canopy.
Bacterial wilt (cucumber beetle vector)	Warm days with cucumber beetle sightings.	Row cover until bloom; scout & treat beetles at 1/plant threshold.
Squash vine borer / squash bug	Warm dry stretch during bloom (summer squash).	Scout stems for frass; pyrethrin at base weekly during flight.
Heat stress / fruit abortion	2+ days ≥ 95°F during flowering.	Morning irrigation; keep bees active with shaded staging.

Greens (lettuce, spinach, kale, chard)

Risk	Weather trigger	First action
Downy mildew (lettuce/spinach)	Cool nights 50–70°F with 6+ hrs leaf wetness.	Resistant varieties; preventive phosphonate; harvest ahead of infection.
Bacterial leaf spot	Warm days (≥75°F) with heavy rain.	Fixed copper; wider spacing; drip instead of overhead.
Aphids & thrips	4+ mild dry days, 65–82°F.	Insecticidal soap or spinosad; row cover on tender greens.
Heat stress / bolting & tipburn	2+ days ≥ 95°F, or highs sustained >85°F.	30–50% shade cloth; irrigate at dawn; harvest before the peak.

Symptom photo guide

Use these photo references during scouting. Match what you see in the field against the sign, then check the weather trigger — if the trigger also fits, act on the first action from the checklist above.

Tomato

Concentric dark rings on lower leaves
Likely: Early blight / Septoria leaf spot
Trigger to confirm: Warm wet days with ≥0.1″ rain
Yellowing between veins, brown edges
Likely: Early blight advancing upward
Trigger to confirm: Repeated leaf-wetness windows
Small dark water-soaked spots
Likely: Bacterial spot / speck
Trigger to confirm: Warm days ≥75°F with heavy rain (≥0.3″)

Pepper

Sunken corky brown spots on fruit
Likely: Bacterial spot (fruit stage)
Trigger to confirm: Warm rain-driven splash events
Small angular leaf lesions
Likely: Bacterial spot (foliar)
Trigger to confirm: Warm wet days, working wet fields
Flower drop with no fruit set
Likely: Heat stress / pollen sterility
Trigger to confirm: 2+ days ≥ 95°F

Eggplant

Round shot-hole punctures across leaves
Likely: Flea beetle feeding
Trigger to confirm: 4+ mild dry days after transplant
Tiny black jumping beetles on foliage
Likely: Flea beetle adults active
Trigger to confirm: Warm dry stretch, no rain to knock down
Sunken dark spots on fruit
Likely: Phomopsis / early blight complex
Trigger to confirm: Warm wet days with leaf wetness

Cucurbits

White powdery coating on leaf surface
Likely: Powdery mildew
Trigger to confirm: 3+ days 68–88°F, RH ≥ 70%, dry
Angular yellow patches bounded by veins
Likely: Downy mildew
Trigger to confirm: Cool nights 50–70°F with 6+ hrs leaf wetness
Sudden wilt with intact green leaves
Likely: Bacterial wilt (cucumber beetle vector)
Trigger to confirm: Warm days with beetle sightings

Greens

Clustered insects on leaf underside
Likely: Aphid colony
Trigger to confirm: 4+ mild dry days, 65–82°F
Brown crispy leaf margins
Likely: Tipburn / heat stress
Trigger to confirm: Highs sustained > 85°F or 2+ days ≥ 95°F
Yellow patches with fuzzy underside
Likely: Downy mildew (lettuce/spinach)
Trigger to confirm: Cool nights + 6+ hrs leaf wetness

Photos are reference illustrations. For confirmed diagnosis on ambiguous cases, send a sample to your state extension plant disease clinic (NCSU, Clemson, UGA, UT, Auburn, UF).

Next 7-day action timeline

A worked example of how a typical Southeast summer week translates weather triggers into daily actions. Swap in your own forecast — the pattern (wet window → preventive spray → drying window → heat push → new wet window) repeats through the season.

Day 1 — Mon

High 88°F / low 68°F, RH 78%, 0.2″ rain overnight, 8 hrs leaf wetness.

Triggers firing

Early blight / Septoria window opens
Bacterial spot risk on tomato & pepper

Do today

Walk tomato & pepper blocks at dawn — flag lower-leaf lesions.
Tank-mix fixed copper + mancozeb on solanaceae before the next wet cycle.
Stay out of wet fields; postpone tying/pruning until foliage is dry.

Day 2 — Tue

High 84°F / low 66°F, RH 85%, 0.1″ rain, 10 hrs leaf wetness.

Triggers firing

Late blight (tomato) — 2nd consecutive wet day
Cucurbit downy mildew watch

Do today

Apply preventive chlorothalonil or copper on tomato before evening dew.
Check the ipmPIPE cucurbit downy mildew map; pre-treat cucumber & melon if a county alert is active.
Log applications with REI/PHI in the Chemical & Fertilizer Log.

Day 3 — Wed

High 90°F / low 70°F, RH 65%, no rain, drying wind.

Triggers firing

Drying window — safe for pruning & harvest

Do today

Prune tomato lower foliage and de-sucker for airflow.
Harvest ripe fruit and cool immediately — heat is climbing.
Refresh mulch on tomato/pepper rows to block soil splash before the next rain.

Day 4 — Thu

High 95°F / low 74°F, RH 55%, no rain.

Triggers firing

Heat stress day 1 — pollen sterility watch

Do today

Irrigate deeply at dawn on pepper, tomato, cucurbits.
Deploy 30% shade cloth on flowering pepper and tender greens.
Harvest greens before 11 a.m. and hydro-cool.

Day 5 — Fri

High 96°F / low 75°F, RH 58%, no rain.

Triggers firing

Heat stress day 2 — blossom drop likely
Aphid/thrips building in dry stretch

Do today

Expect flower drop on pepper — do not panic-spray; keep water on.
Scout greens & brassica undersides for aphids; release lacewings or apply insecticidal soap at threshold.
Skip sulfur on cucurbits — phytotoxic above 90°F.

Day 6 — Sat

High 87°F / low 70°F, RH 72%, 0.05″ scattered showers.

Triggers firing

Powdery mildew window (warm, humid, still mostly dry)

Do today

Apply potassium bicarbonate or a labeled biofungicide on cucurbits & squash.
Thin cucurbit canopy so leaves dry by midday.
Re-scout tomato for early blight progression from Day 1–2 wet cycle.

Day 7 — Sun

High 82°F / low 65°F, RH 90%, 0.4″ rain forecast overnight.

Triggers firing

Bacterial spot splash event
Late blight wet-window reopens

Do today

Pre-treat tomato & pepper with fixed copper before the evening front arrives.
Do NOT work fields tomorrow morning while foliage is wet — bacteria spread on hands & tools.
Plan Monday's scout route: tomato → pepper → cucurbits, lowest-elevation blocks first.

This is a reference week, not a forecast. Sign in to Pest Watch to generate the same day-by-day plan against your farm's live 7-day forecast and active plantings.

How BAU's Pest Watch automates this

Pest Watch pulls your farm's 7-day forecast (temperatures, precipitation, hourly humidity for a leaf-wetness proxy) and evaluates it against the rules above for the crops you have in the ground. You get a severity-ranked list of risks with the date window, the reason, and the recommended action — no manual scouting log needed to catch the pattern.

Pest Watch lives inside your BAU dashboard. Sign in and connect a farm location and at least one active planting to see live risk flags for your fields.

Open Pest Watch

Live 7-day risk flags for the crops you have in the ground.

What this guide is not

A weather-based risk model tells you when conditions favor a pathogen — it does not replace field scouting or a diagnostic lab. For confirmed identification, send samples to your state extension plant disease clinic (NCSU, Clemson, UGA, UT, Auburn, UF). Always follow the pesticide label — REI, PHI, and rate limits are legal requirements, not suggestions.

Pest & Disease Risk Guide for Southeast Specialty Crops

The seven risks we track

Late blight (Phytophthora infestans)

Early blight & Septoria leaf spot

Cucurbit downy mildew

Powdery mildew

Bacterial spot & speck

Heat stress (pollen sterility, blossom drop)

Aphid & thrips pressure

Crop-specific checklists

Tomato

Pepper

Eggplant

Cucurbits (cucumber, melon, squash, pumpkin)

Greens (lettuce, spinach, kale, chard)

Symptom photo guide

Tomato

Pepper

Eggplant

Cucurbits

Greens

Next 7-day action timeline

Day 1 — Mon

Day 2 — Tue

Day 3 — Wed

Day 4 — Thu

Day 5 — Fri

Day 6 — Sat

Day 7 — Sun

How BAU's Pest Watch automates this

Open Pest Watch

What this guide is not

Run this in BAU, not a spreadsheet