Mealybugs

Photo is a bit distant so cannot see the details of the infestation, but are the white markings on the left side of the plant mealybugs, especially if they have a cottony, fuzzy appearance and feel sticky? Mealybugs suck the nutrients out of the plant and will eventually kill it if left untreated. Consult your local garden center for confirmation of the problem and remedies. If they are mealybugs, you can hand remove them with a cotton swab dipped in alcohol and then rinsed off, but if there are a lot, you may want to wash them off with a strong stream of water, followed by a spray with insecticidal soap or pyrethrin product. If this is just a reflection, then the yellowing of the leaves may be due to irregular watering or possibly it is a plant that is sensitive to salts in the water.