Can somebody know what is happening with the new leaf that has black spots? This is a Persian lemon

Omg so is not a treatment for this disease

She has a general mineral deficiency (in this case, it could be iron, magnesium, molybdenum, or zinc.) but it's easily remedied with a few handfuls of kelp meal sprinkled around the base of your plant and by adding a few pinches of sea salt to each watering = ) If you want to go the extra mile, you could also try some organic fertilizer, (worm castings, fish supplements, anything from Espoma Organics, or nutrients from Kelp4Less (a good company) but the above two options are a sure fire way to get your plants in tip top shape and restore their mineral balances to optimum levels! = )

While it's hard to see without a close up, the above-mentioned will strengthen your plants naturally, and make them resistant and less appealing to critters 🌴