Hello, calathea (Calathea, plant care and growing guide) seems to be attacked by mites (Mites in ornamental plants - pest management). Thus, for control, it is recommended to carry out 1-2 treatments, 7-10 days apart with an insecticide such as , in a dose of 5 ml/10 L water, applied by foliar spray (on the upper and lower part of the leaves, as well as on the stem). In order to increase the effectiveness of the insecticide, it is indicated to add an adjuvant such as , in a dose of 2 ml/10 L to the spraying solution. It is important to prepare a volume of solution corresponding to a single treatment (respecting the mentioned dosage), as the mixture already prepared does not have a valability longer than 24 hours. Spray () the solution as finely as possible, so as to achieve a more uniform distribution of the solution on the plant.
10-14 days after applying the insecticide treatment, it is advisable to apply a foliar fertilizer that supports the plants in overcoming periods of stress and contributes to maintaining their health, such as or , applied directly by spraying, according to the recommendations on the label, depending on the product chosen.