Pests & diseases › Potato Blight
Potato Blight
Same pathogen as tomato blight (Phytophthora infestans). Wrecks the foliage, then rots the tubers.
Symptoms
- Dark patches on leaves spreading rapidly in humid weather
- Whole plant collapsing within days
- Tubers with reddish-brown rot under the skin
- Stored potatoes turning slimy
Lifecycle
July to September is peak season. Spreads fastest in warm wet weather.
What to do
- Cut off all haulms (foliage) at the very first sign — do not compost
- Wait 2–3 weeks before lifting tubers so spores die off on the soil surface
- Lift on a dry day and dry skins thoroughly before storing
If it's bad
- Copper fungicide as a preventative — never as a cure
Stop it coming back
- First and second earlies are usually safe — they're out of the ground before blight strikes
- Choose resistant maincrop varieties (Sarpo range, Carolus, Cara)
- Earth up well to protect tubers from spores washing down
- Three-year rotation
Crops it goes for
Plan the plot, track every sowing, cook the harvest
Sowing reminders and harvest forecasts for your own frost dates, the Seed Tin, Scan Centre for any label or packet, and the Potty Mouth Garden Club. Free to start.