I repotted my basil plant yesterday as it was in a small seedling bag. Today when I checked on my plant, all of the leaves even the small ones that are growing, had black dots all over. Please help I’m a newbie plant parent. I also live in a tropical country so frost is out of the question.
I had a similar issue with my basil, and from my research, I think it was a fungus. I also had aphids, though mostly on my neighboring cilantro plants. I cut off all leaves on my basil plants and sprayed with soapy water (read this could help get rid of aphids) every two days. Many of the next leaves that grew in did not have the black spots anymore, but not all.
Background: Also a fairly new gardener so my knowledge is very limited. My basil, which I didn’t use much so didn’t put a lot of effort into problem solving, was planted along with cilantro in a wood wine box outdoors. I also live in a warm climate so frost could not have been a culprit.
We note that the spots are tiny, circular and fairly widely spaced. We also know that basil has a soft leaf and is vulnerable to attack from both upper and lower leaf surfaces. If it was a fungus we would expect larger patches and some sort of residue on the leaf, so I think we can rule out this type of disease. Looking at insects we can note that some insect species take up residence on a plant that is useful to them, like aphids, mealybugs, scale, whitefly and so on but evidently there is no sign of patches of them here. This leaves insects that come and go, say flying adults that land on the leaf, nibble or pierce and drink and then leave. In this last group we can think of thrips and beetles.
You might want to keep a close eye for these insects on other plants in your neighbourhood/house and be sensitive to occasional visitors on your basil plants. The marks are not as dense as thrips are capable of producing, so at this point the problem is not severe but could quickly become so if there are no alternate food sources locally.