Hello. The plants seem to be attacked by mites (small pests, hardly visible to the naked eye). Against them you can carry out 1-2 treatments, at 7 days intervals, using an insecticide-acaricide such as: , in a dose of 8 ml/10 L water, by foliar spraying.
It is important to prepare a volume of solution corresponding to a single treatment (respecting the mentioned dosage), because the already prepared mixture does not have a shelf life longer than 24 hours. It is also important to carry out treatments early in the morning, when temperatures are not very high.
At the same time as the treatment is carried out, in order to provide the plants with the necessary nutrients and to revitalize them, it is also advisable to regularly apply a fertilizer such as by watering, according to the instructions on the label.