Late blight's original host. A potato crop can go from first lesion to total loss in ten days, so protectant spraying starts before symptoms appear, not after.
- Grown in
- India, China, Kenya, Russia, Germany, Peru
- Season
- Cool season, 90–120 days
- Soil & pH
- Loose, well-drained sandy loam, pH 5.0–6.0
What to scout for on Potato
- Water-soaked dark blotches with white sporulation underneath
- Firm brown rot when a tuber is cut open
- Rolled, leathery upper leaves — leafroll virus
- Blackleg softening at the stem base after wet weather
Diseases that attack Potato
Late Blight
Phytophthora infestans
Bacterial Wilt
Ralstonia solanacearum / Erwinia tracheiphila
Aphid Infestation
Aphidoidea
Products you can buy for Potato
Typical registered products for the diseases above, with active ingredient, mixing rate, spray interval and pre-harvest interval. Rotate FRAC/IRAC groups to avoid resistance.
Mancozeb 80% WP
Active ingredient: Mancozeb
- Dose:
- 2.0–2.5 g per litre of water (2.0–2.5 kg/ha in 800–1000 L)
- Interval:
- Every 7 days during cool, wet weather
- PHI:
- 7 days
Protectant only — it must be on the leaf before spores land. Re-apply after 20 mm of rain.
Copper oxychloride 50% WP
Active ingredient: Copper oxychloride
- Dose:
- 3 g per litre (2.5–3 kg/ha)
- Interval:
- Every 7–10 days
- PHI:
- 3–5 days
Approved for most organic programmes. Do not spray in full midday sun on young foliage — copper can scorch.
Ridomil Gold MZ (metalaxyl-M + mancozeb)
Active ingredient: Metalaxyl-M 4% + Mancozeb 64%
- Dose:
- 2.5 g per litre (2.5 kg/ha)
- Interval:
- Every 10–14 days, maximum 3 applications per season
- PHI:
- 14 days
Curative for 2–3 days after infection. Never use alone or more than 3 times — Phytophthora develops metalaxyl resistance quickly.
Cymoxanil + famoxadone
Active ingredient: Cymoxanil 30% + Famoxadone 22.5%
- Dose:
- 0.4 g per litre (400 g/ha)
- Interval:
- Every 10 days
- PHI:
- 7 days
Excellent rotation partner with mancozeb; alternate FRAC groups on every second spray.
Copper hydroxide 77% WP
Active ingredient: Copper hydroxide
- Dose:
- 2–3 g per litre as a soil drench and foliar spray
- Interval:
- Every 10 days as suppression only
- PHI:
- 1–3 days
Copper suppresses surface spread — it cannot cure a vascular infection. Roguing is still mandatory.
Bleaching powder / calcium hypochlorite
Active ingredient: Calcium hypochlorite 33%
- Dose:
- 10–15 kg/ha broadcast into infested beds, or 1% solution for tool dipping
- Interval:
- Once before planting; dip tools between every plant
- PHI:
- Not applicable (pre-plant)
The single most effective intervention: Ralstonia survives in soil and moves on unsanitised knives.
Doses shown are typical registered field rates. Always read the product label, confirm the product is registered for your crop and country, respect the pre-harvest interval (PHI), and wear the protective equipment the label specifies. PlantWatch AI provides agronomic guidance, not a legal spray recommendation.
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