I have a yellow chilli that is 40 days old. It appears healthy but as of the last couple days the leaves towards the bottom have been turning yellowing and getting spots that are darker on the edges and grey in the middle. In the underside are all kinds of these very tiny black dots. Any clues what’s wrong? A couple leaves Have fallen off
I’m so sorry, but your chili is infested with thrips. Those pale areas and black spots show that the damage is already done by thrips.
One option is to remove the affected leaves asap and monitor the plants carefully and all the other plants around it. If the thrips have not spread yet around the plants and the infestation is fresh it is possible you get rid of those by removing affected leaves.
If they spread they are quite impossible to get rid off and all plants need to be thrown out.