I think it may be aphids so have a look and see if you can spot them. As PF says, remove all affected leaves and destroy them. You may be able to rinse off any eggs or aphids left o the rest of the plant and then you need to keep an eye out every day and squish any that return with your fingers.
Vendée - 20kms from Atlantic coast.
"The price good men (and women) pay for indifference to public affairs is to be ruled by evil men (and women)."
Could it be due to lack of light? They are on a south facing window but only get maybe 1 or 2hrs if sunlight a day since the sun is so low. They have all died since I removed some leaves.
Basil comes from Thailand, so for it to grow well you want lots of light and warmth - not easy in December in the UK. If you try with them again, keep them in a sunny position in the day, and keep them warm when the sun is down and not too much water. I just grow basil in the summer months in my greenhouse but if I need fresh in the winter I buy it.
Billericay - Essex
Knowledge is knowing that a tomato is a fruit. Wisdom is not putting it in a fruit salad.
I'd agree with Pete - it's nigh on impossible to grow it here in the winter. If you wannt to have fresh basil through winter, another way of doing it is to grow loads more in summer, then freeze it. It's not so good for sprinkling on anything, as it breaks down when defrosted, but it's ideal for stirring into a dish at the end of cooking.
It's a place where beautiful isn't enough of a word....
I live in west central Scotland - not where that photo is...
I agree with Philippa, it grows so easy from seed it’s not worth keeping it over winter. Sow seeds in succession. probably white fly in the OP’s photo.
Gardening on the wild, windy west side of Dartmoor.
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If you try with them again, keep them in a sunny position in the day, and keep them warm when the sun is down and not too much water.
I just grow basil in the summer months in my greenhouse but if I need fresh in the winter I buy it.
Billericay - Essex
Knowledge is knowing that a tomato is a fruit.
Wisdom is not putting it in a fruit salad.
If you wannt to have fresh basil through winter, another way of doing it is to grow loads more in summer, then freeze it. It's not so good for sprinkling on anything, as it breaks down when defrosted, but it's ideal for stirring into a dish at the end of cooking.
I live in west central Scotland - not where that photo is...
probably white fly in the OP’s photo.