TopVeg has (inadvertently) demonstrated that potato blight spreads in warm wet weather.
When the weather was warm and wet, and for some reason a cloche had been put over half the potato row, so covering those potato leaves and keeping the rain off.
blight in uncovered potatoes
The covered potatoes were healthy,
healthy potato leaf
but those plants left out in the rain were decimated.
blighty potato row
This all happened in a week, and it demonstrates that blight flourishes in warm wet weather, and it is really worth applying a protective spray to potato crops.
Potato blight is caused by a fungus, (latin name – Phytophthora infestans), which spreads rapidly in warm, moist conditions.
blight on leaf tips
Dark brown patches and yellowing appear on the leaves, which turn black, before a white bloom develops on the underside as the foliage dies. The white bloom is made up of the fungal spores which are then blown by the wind and spread the infection. The leaves die off, and tuber growth stops. The spores drop onto the tubers in the ground and cause them to go brown and rot. The potatoes, and the whole area, smell rancid and rotten.
Vegetable gardeners should avoid, prevent and delay the onset of blight by:
- using good quality, blight-free potato seed
- growing blight resistant varieties
- aiming for early harvest, before blight becomes a problem
- chitting, to bring harvest forward
- planting as early as possible, to bring harvest early
- mixing varieties, as some are more prone to blight than others
- avoiding sheltered positions, as blight thrives in humid areas
- practising good vegetable garden hygiene – tidy away all waste potato haulm and tubers & burn. Do not leave on the compost heap. All tiny potatoes & damaged tubers must be lifted from the ground, & thoroughly harvested. If not, they will grow the following year
(volunteers) and act as a host for blight. All volunteers must be removed as soon as seen - watching neighbouring potato plots to make sure they have not got blight
- spray with a preventative fungicide every 14 days once the leaves have met in the row. Click this link for a spray that is available on Amazon (affiliate link):
blight on new shoots
- watch the weather and listen for blight warnings & Beaumont periods
- remove the leaves and burn them
- lift potatoes as soon as possible – but leave those which actually had blight for 14 days, to avoid spreading the spores onto the tubers and causing them to rot in store.
Some varieties are more susceptible than others.
- Varieties susceptible to potato blight include:
King Edward, Arran Comet, Arran Pilot, Desiree, Epicure, Foremost,
Golden Wonder, Home Guard, Kerr’s Pink, Majestic, Maris Bard, Maris
Peer, Maris Piper, Nicola, Rocket, Russet Burbank, Sharpe’s Express, and
Ulster Chieftain.
- Varieties with some resistance to potato blight include:
Cara, Estima, Kondor, Orla, Pentland Dell, Pentland Crown, Romano,
Sante, Valor, Mira, Eve Balfour, Axona and Remarka.
It is important to control potato blight as it can cause total crop failure.