White spots on calathea leaves can signal various underlying issues, ranging from common pests to environmental stressors or fungal developments. Understanding the cause of these spots is the first step toward effective treatment and maintaining your calathea’s health.
Pest-Related White Spots
Pests are a common reason for white spots on calathea leaves, often leaving other tell-tale signs. Inspection is key to identifying the culprit and applying the correct treatment.
Spider mites appear as tiny red, brown, or black dots on the undersides of leaves. Their feeding causes small, white or yellowish spots (stippling) on the leaf surface. Fine webbing may also be visible, particularly where the leaf meets the stem. To manage them, wipe leaves with a damp cloth, then apply insecticidal soap or neem oil every 5-7 days for several weeks. Increasing ambient humidity can also deter these pests.
Mealybugs are identified by their soft, oval bodies covered in white, cottony wax. They cluster in leaf axils, along veins, or on the undersides of leaves, appearing as fuzzy white masses. Their feeding results in sticky honeydew, which can lead to sooty mold. Small infestations can be treated by dabbing mealybugs with a cotton swab dipped in rubbing alcohol. For larger outbreaks, insecticidal soap or neem oil sprayed on all plant surfaces can be effective.
Thrips are slender, tiny insects that feed by rasping plant tissue and sucking sap. This damage causes silvery streaks or stippling on the leaves, which can then turn into pale or white spots as affected cells dry out. They are found on the undersides of leaves. Treatment includes regular applications of neem oil or insecticidal soap.
Scale insects appear as small, immobile bumps on plant stems and leaves. Some species are pale or translucent, appearing as white spots where they attach and feed. Their feeding can lead to yellowing of the leaf tissue around the attachment point, which may then dry out. Manual removal involves gently scraping them off with a fingernail or soft brush. Following removal, insecticidal soap or neem oil can be applied to address any remaining nymphs.
Environmental Factors Causing White Spots
Various environmental conditions can also cause white spots on calathea leaves. These issues often stem from improper care practices.
Mineral deposits from hard water are a common cause of white, powdery residue, especially after misting or overhead watering. As water evaporates, it leaves behind dissolved minerals. These spots are cosmetic but can impede photosynthesis. Using distilled, filtered, or rainwater for your calathea eliminates this issue. Regularly wiping the leaves with a soft, damp cloth also removes existing deposits.
Fertilizer residue or burn can appear as white or brownish crusty spots on the leaf surface or edges. This occurs due to over-fertilization, concentrated fertilizer, or splashing it onto foliage. Excess salts accumulate and crystallize on the leaf. To prevent this, always dilute liquid fertilizers according to package directions. If residue appears, flush the soil thoroughly with plain water to wash out excess salts.
Cold damage or drafts can cause sudden changes in leaf appearance, including pale or white spots. Calatheas are sensitive to temperature fluctuations and prefer consistent, warm conditions. Exposure to cold air can damage leaf cells, causing them to turn white. Moving the plant to a more stable environment, away from direct drafts and maintaining temperatures above 60°F (15°C), helps prevent this damage.
Fungal Issues and Other Concerns
Certain fungal conditions and dust can also cause white spots on calathea leaves. Recognizing these appearances helps in addressing them.
Powdery mildew appears as fuzzy, powdery white patches on the surface of leaves, often resembling a dusting of flour. This fungal disease thrives in conditions with poor air circulation and high humidity. Unlike mineral deposits, powdery mildew can be wiped off. Improving air circulation around the plant and reducing excessive leaf wetness helps prevent its spread. Applying neem oil or a specific fungicide can treat active infections.
Dust accumulation can be mistaken for white spots or a general white film. Over time, household dust settles on the leaves, creating a dull, whitish layer. This accumulation can hinder photosynthesis and obscure early signs of pests. Regularly wiping the leaves with a soft, damp cloth removes dust and allows for close inspection of the plant’s health.
Preventing Future White Spots
Proactive measures are important for maintaining your calathea’s health and preventing white spots. Consistent care practices create an environment where your plant can thrive.
Quarantining new plants for two to four weeks before introducing them to your collection prevents pest introduction. This isolation period allows you to observe the new plant for any signs of pests or diseases. Regular inspection of your calathea’s leaves and stems allows for early detection of any issues.
Calatheas prefer consistently moist soil but are susceptible to root rot if overwatered. Ensure pots have adequate drainage holes to prevent waterlogging, which can stress the plant. Calatheas thrive in bright, indirect light and high humidity. Providing these conditions helps deter pests and reduces plant stress.
Good air circulation around your calathea prevents stagnant, humid conditions that favor fungal growth, such as powdery mildew. Avoid placing plants too close together. Regularly wiping leaves removes dust, disrupts pest activity, and allows for close examination. If hard tap water is an issue, using filtered, distilled, or rainwater prevents mineral deposits.