Hello. The deterioration of plants can be caused by a combination of biotic and abiotic factors, but the nature of the disease cannot be accurately determined from the photos and information provided (Indoor plants - symptoms, causes, solutions). Some of the symptoms on the leaves resemble those caused by a bacterial infection (especially the yellow spots on the leaves of Alocasia).
For the time being, you can consider removing the affected leaves (with a disinfected tool) and carrying out two treatments (at 7-10 day intervals) with a fungicide such as , by foliar spraying, in a dose of 20 g/10 L water. Spray the solution as finely as possible, so as to achieve an even distribution on the plants, both on the underside and topside of the leaves and on the stems (). It is advisable to prepare a volume of solution corresponding to a single treatment (respecting the mentioned dosage), as the already prepared mixture does not have a shelf life longer than 24 hours.
Subsequently, 7-10 days after the completion of the foliar treatments, you can consider a treatment with a biological fungicide such as , by watering at the roots, in a dose of 10 g/ 10 L water. In this case as well, it is important to prepare a volume of solution corresponding to a single treatment (respecting the mentioned dosage), as the already prepared mixture does not have a shelf life longer than 24 hours.
Also, 7-10 days after the completion of the foliar treatments, you can consider applying a fertilizer that stimulates the regeneration of plants after certain stress conditions, such as , according to the instructions in the product description.
It is not possible to specify exactly how the plants will develop in the future. For more detailed information on the care of these plants, please consult the following articles: Alocasia, plant care and growing guide, Ficus, plant care and growing guide, Philodendron, plant care and growing guide.