Hello. From the photos you have inserted, the plant seems to be suffering from a thrips attack (Thrips - pest management). It also shows symptoms similar to those caused by a bacteriosis. Against these pests you can treat with the insecticide and the adjuvant (the leaves of Monstera plants are glossy and the solution slides off the leaves, so this adjuvant helps to fix the solution on the leaves). These products should be added to 10 l of water. 7 days after this treatment, a treatment with , 20 g/10 L water is recommended against the bacteriosis. It is advisable to spray the solutions as finely as possible, so as to achieve a uniform distribution on the plant, both on the underside and the topside of the leaves and on the stem. It is advisable to prepare a volume of solution corresponding to a single treatment (respecting the mentioned dosage), as the already prepared mixture has a shelf life of no more than 24 hours. The treatments can also be applied to the other plants in the premises (if any).
In order to help the plant to overcome the period of stress suffered, 7-10 days after the end of the treatments it is recommended to use a foliar fertilizer such as , applied according to the information on the product label. It is also important to remove the leaves that are severely affected, leaving a few on the plant to help it continue its processes (photosynthesis, transpiration, respiration), and after the appearance of new leaves, the rest of the affected leaves can be removed for a more aesthetically pleasing appearance of the plant. More information on the care of this species can be found in our article in the Armuro Community: Monstera, plant care and growing guide.