What Causes Yellow Leaves on Prayer Plants
Environmental Stress
By far the most common Maranta prayer plant problems are caused by incorrect care. Bright lighting or excessive phosphate or fluoride can cause leaf tips and margins to burn, leaving a band of yellow tissue between the healthy and dead tissues. Chlorosis causes yellow prayer plant foliage, especially on younger leaves. Move your plant to a location with indirect light and begin watering with purified water. A dose of liquid iron fertilizer mixed per package directions can help correct chlorosis, provided the pH of your medium is around 6.0. A soil test may be in order, or it could be time to repot.
Fungal Disease
Helminthosporium leaf spot is a fungal disease that causes small, water-soaked spots to appear on prayer plant leaves. These spots soon yellow and spread, eventually becoming tan areas with yellow halos. This fungus takes hold when plants are chronically over-irrigated and leaves frequently are covered in standing water. Correct the irrigation problem to eliminate future risk of disease and water only at the base of the plant in the morning, so that water evaporates from splashed surfaces quickly. An application of neem oil or the fungicide chlorothalonil can kill active disease, but prevention of future outbreaks is vital.
Cucumber Mosaic Virus
The cucumber mosaic virus may be responsible for yellowing leaves on Maranta, especially if the yellowing alternates with otherwise healthy green tissue. New leaves may emerge small and distorted, older leaves develop yellow line patterns across their surfaces. Unfortunately, there’s nothing you can do for plant viruses. It’s best to destroy your plant to prevent other houseplants from contracting the virus.