After a busy year in the garden, July is usually the month by which growers can finally start to enjoy their bounties. It’s a good time to pick courgettes before they turn into marrows, get those glorious tomatoes off the vine, and harvest some early stone fruits, like nectarines and plums.
But in his gardening blog’s July entry, Monty Don said that a veg-ruining fungus can “develop very fast when the temperature is high and the air humid for 23 hours, and these conditions are becoming increasingly common in July”.
Potato blight, which has become more common in the UK as summer temperatures trend upwards, can be prevented if spotted early.
What is potato blight?
It includes fungi and fungus-like organisms that start on potato leaves and stems and then quickly spread to the tuber (the part we eat).
Blight makes potatoes decay and collapse. It’s the plant’s “most serious and damaging disease,” the Royal Horticultural Society said.
For Monty Don, increasingly hot weather has made the risk of blight so great that he now only grows “first earlies”, sometimes known as new potatoes.
These are ready for harvest before peak blight season begins, so they’re less likely to suffer from the disease.
What are the signs of potato blight?
Signs of potato blight include:
Brown, watery-looking leaf rot which spreads quickly and leads to shrivelling and rot,
Sometimes, brown patches on stems,
Discoloured patches on potatoes,
Red-brown rot beneath the tubers’ skin.
Sometimes, affected potatoes don’t seem all that affected by blight – in fact the damage might not even be visible – but a “secondary rot” can kick in once they’re stored and affect other spuds.
How can I prevent potato blight?
“The crop can be saved if… foliage is removed [as soon as blight’s] tell-tale chocolate-coloured circular areas of the leaves are noticed,” Monty Don suggested.
But this has to be caught very early as blight spreads fast.
“Remove all foliage and compost it (the fungi do not survive the composting process) and make sure that there is a good soil covering over the tubers. Then wait for a dry day and harvest the crop,” the gardener continued.
He generally digs his first potatoes on 8 July – his birthday. But the RHS says we should “lift as soon as possible if blight appears in the crop and tubers are of useable size”.
Don’t place potatoes that you think have blight in storage, and check regularly on those you’re stashing away, as secondary rot can be very sly.
If planting potatoes, choose a reputable seller, choose a site with good airflow, and leave space between plants.
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