Mary Jane has some blotchy patches

[gin_tonic]

my brother called me up today in a panic. He's got a Mary Jane plant (one out of four) that looks totally fine one minute and weird the next.
He just found these weird blotchy patches on some of the leaves, like something's been taking little bites out of them.

He checked for bugs with his jeweller's loop, but he's a total newbie and couldn't see anything.
Has anyone seen this before? Any ideas what's going on?

 

[HydroG33k]

Those spots might mean your plant isn't getting the right food, or it could be spider mites. Take a look for any bugs or webs. You might also want to test your soil to see if it needs different nutrients. If you do find pests, neem oil or a fungicide could be useful.

 

[HELYAB]

Those blotchy patches could be caused by a few things. Even if you didn't see bugs it can be tough to spot tiny critters like thrips or spider mites since they often hide on the underside of leaves. A bright light and magnification help. If it's pests wiping the leaves gently and using neem oil or insecticidal soap can help. If no pests appear consider nutrient imbalance, sometimes calcium or magnesium deficiency or pH swings produce mottled leaves. Check your nutrient solution or soil pH and adjust within the recommended range. Make sure there are no water droplets burning leaves under intense light. Removing the worst leaves and monitoring new growth is often the best way to tell if your adjustments are working.

 

[wingit88]

Those blotchy patches could be caused by a few things. Even if you didn't see bugs it can be tough to spot tiny critters like thrips or spider mites since they often hide on the underside of leaves. A bright light and magnification help. If it's pests wiping the leaves gently and using neem oil or insecticidal soap can help. If no pests appear consider nutrient imbalance, sometimes calcium or magnesium deficiency or pH swings produce mottled leaves. Check your nutrient solution or soil pH and adjust within the recommended range. Make sure there are no water droplets burning leaves under intense light. Removing the worst leaves and monitoring new growth is often the best way to tell if your adjustments are working.

Appreciate this! I’ve got a few chili plants on my balcony and just saw some blotchy leaves. Never used neem oil. how often do you apply it if pests are the issue?