I have a basil plant in my flat which has recently developed some light patchy areas with small black spots. Can anyone tell me what is causing it?

I occasionally use some left over Tomorite to feed it and the plant is in the window where it gets lots of sun, but is generally kept watered.

I'm wondering if it may be caused by small flies that I occasionally see around the bottom of the plant.


basil leaf with spots basil plant with spots underside of basil leaf

  • Small flies down near soil are often fungus gnats: ext.colostate.edu/pubs/insect/05584.html How often are you watering? Commented Aug 24, 2015 at 13:56
  • 1
    @leeb: Have you found the cause of the problem and how to fix it?
    – Thanh Bui
    Commented Aug 28, 2020 at 7:10
  • @ThanhBui I fixed it by buying a new basil plant ;) Don't think there's an easy way of curing this :(
    – leeb
    Commented Jan 30, 2021 at 14:13

2 Answers 2


Leaf Miner damage and controlLooks like a leaf-miner of some sort...the light colored wiggly lines is what was eaten and the black is fracas...poop. Gotta see the insect itself, really to suggest how to treat. Is this plant outdoors or indoors? Please send pictures of the undersides of the leaves. Some leaf miners actually live IN the leaf. If you could turn the leaf over, look for slight bumps. Use a razor blade and carefully cut the bump to shave leaf and see if you can find insect. It'll probably look like a tiny worm...investigate while leaves are warmed from the sun and also while night. If you can't see anymore damage happening it might be because the insect has matured and flown away leaving eggs inside the leaf. Just use leaves that are new and undamaged for now.

In this article I've attached there is a paragraph on how to find the insect...if it is still possible. Putting a few leaves in a ziploc so that when larvae are matured they can't fly away. Those tiny flies WERE probably the adult leaf miners! Are these basil plants planted in garden soil or sterilized potting soil?? And the article talks about using NEEM. They said it was NATURAL. Hey 'Natural' can be VERY TOXIC. I've used NEEM and it works very well on ornamentals but I wouldn't use it on my basil!! Heck, take nicotine! Very natural, but it has got one of the most toxic LD50 (lethal dose for half the population so lower the number, higher the lethality)!! When did you first see this damage? Using garden soil in pots is a possible reason your plant got this insect. Big no-no! Always use sterilized potting soil (infused with bacteria and mycorrhizae) to plant anything in pots! Basil is an annual and does have a very short useable life. Next batch scrub those pots and use potting soil. No rocks or gravel in the bottom...actually inhibits drainage!! I am just trying to cover bases by making lots of assumptions!! Let us know what you find and send a few more pictures!!

  • Thanks, this does seem like it is probably the cause. It's an indoor plant which I have had for a good few months now. I have edited the original post and added another picture of the underside of a leaf, though it's difficult to get a good close up. I can just about see some very small brown lumps, which I guess is the larvae?
    – leeb
    Commented Aug 24, 2015 at 21:11
  • Did you try to operate with a razor? Grin!! Where did your soil come from? It is unusual to get insects like this for indoor plants...probably came from the nursery...or did you plant from seed?
    – stormy
    Commented Aug 25, 2015 at 23:42
  • Neem oil is not toxic. They consume it in India for birth control. People apply it to their skin, etc. Neem is very very safe.
    – Spencer
    Commented Sep 24, 2015 at 22:33
  • Hi Spencer...Neem oil differs greatly with manufacturers. Have you read any of their MSDS sheets? Of manufacturers in this country. It might and must be different between US and India, yeah? There are 'brands' that say their neem oil is safe for bees for instance and then there are others that warn to not use during the day to avoid bees. I would NEVER call anything manufactured by someone else SAFE. Never. Even food...grins.
    – stormy
    Commented Sep 24, 2015 at 22:39
  • @stormy Ok well you can be crazy pants all you like, but 100% pure Neem oil is non-toxic and safe to consume. If you're going to argue that pesticides mixed with Neem oil is not safe to consume, then well, yeah, you're right. But Neem oil itself is completely safe. If you want to talk about bees, sure, if you spray a bee in the face with this stuff it is toxic to them. Here's an msds sheet from where I got mine: dyna-gro.com/Website%20pdf%20Files/MSDS%20Neem%20Oil.pdf Safe to consume for humans.
    – Spencer
    Commented Sep 25, 2015 at 0:10

Thrips. 100% for sure. I have fought the thrips battle for many years in my indoor farm. That is a classic picture of thrips infestation. Best thing i’ve found yet to fight them is predatory mites.

I recommend using Neoseiulus Cucumeris (Amblyseius cucumeris) which you can also order from online sellers.

  • I have the same problem, and found at least one of the insects. It looks like Thrips.
    – Wimateeka
    Commented Sep 11, 2020 at 11:56

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.