Calathea is a beautiful houseplant but finicky and prone to yellow spots on leaves.
If your Calathea leaves have yellow spots, don’t worry. I’ll break down the steps for restoring your attractiveness and keeping it that way.
Pest infestations and leaf spot diseases are the most common causes of yellow spots on Calathea foliage.
Yellow spots between veins usually indicate an excess of light, a lack of water, low humidity, and nutritional deficiencies.
Maintain 60% humidity, cut back on severely infected plants, and treat them as needed.
Why Do Leaves on My Calathea Have Yellow Spots?
[1] Pseudomonas Leaf Spot
The bacterial disease Pseudomonas leaf spot affects Calathea plants. Pseudomonas cichorii is the most common bacterial pathogen.
Long periods of wet leaves and highly humid environments promote the growth and spread of bacterial infection.
The bacterial leaf spot disease causes relatively large wet or soggy spots that start dark green and eventually turn black.
These water-soaked areas may have a yellow halo, giving the appearance of yellow concentric zones on the leaves.
Calathea makoyana, Calathea vittata, and Maranta leuconeura are among the Calathea species and cultivars resistant to Pseudomonas leaf blight.
Stromanthe amabilis ‘Burle Marx,’ Calathea roseo-picta, and Calathea ornata, on the other hand, are susceptible to bacterial infection, and yellow-ringed spots can grow to be an inch wide.
There are rarely more than two Pseudomonas spots on the same leaf. This is because most bacterial pathogen-infected leaves fall off before they are completely covered.
Treatment, Control, and Prevention of Pseudomonas Leaf Spot in Calatheas
- Because Pseudomonas Leaf Spot is a systemic infection, controlling it is difficult.
- Overwatering, leaf wetting, and overhead irrigation are all standard control methods. Accepting these care changes will reduce the conditions for bacterium spread and infection.
- As a preventive measure, copper-based bactericides can be used.
- Water your Calatheas from the bottom to avoid splashing water on the leaves.
- To improve airflow and reduce humidity around your Calathea, space your plants, vent, and use a fan.
- When the leaves of your Calathea plants are wet, avoid touching them.
[2] Bacterial Leaf Spot
Numerous other bacterial leaf spot diseases can also cause yellow spots on the leaves of your Calathea, not just Pseudomonas leaf spot.
If your Calathea plant is sick, it will likely have water-soaked spots. They can appear as dark brown spots with yellow borders or watery lesions with black edges.
Additionally, the bacterial disease can cause the appearance of contrasting dark and light patches on the plant’s leaves.
However, bacterial leaf spots are frequently asymmetrical, can be as large as half an inch in diameter, and sometimes secrete a sticky substance from their centers.
They may grow or stay the same size depending on the environment.
For example, wet, dark brown spots with yellow halos grow and merge into larger blotches when humid air is humid.
However, these yellow rings around spots won’t grow under drier conditions.
So the spots won’t spread but will dry out and turn brownish red, giving your Calathea a spotted, yellow appearance.
The tips and edges of infected leaves may turn brownish yellow, dry out, and fall off. It makes the tips and edges of the leaves feel papery and frail.
The bacterial leaf spot disease spreads quickly from plant to plant.
Most of the time, the bacteria that cause disease overwinter in dead plant parts and splash onto wet leaves when watering. Cool and wet conditions aid their spread.
Treatment and Prevention of Calathea Bacterial Leaf Spot
If you find a bacterial leaf spot, act quickly to prevent the infection from spreading.
Remove and discard infected foliage as soon as possible to prevent it from spreading.
In the early stages of infection, use a copper-based bactericide.
Prevention is a multi-pronged approach:
- Avoid watering from above.
- Water your Calatheas early in the morning to reduce leaf wetting.
- When the leaves are wet, avoid handling them.
- Use sanitary gardening techniques.
- Remove any dead plant matter and debris as soon as possible.
[3] Anthracnose of Calathea
Anthracnose is a common fungal disease that causes Calathea leaf spots. This infection appears on the lower sides of foliage as smudges of slight tan, yellow, or brown spots.
Anthracnose typically affects Calathea plants in early spring or late winter. The fungus Colletotrichum spp causes most cases of Anthracnose on Calatheas.
The fungus usually lives and overwinters in the soil. As a result, it spreads via soil splashes. It thrives in cool, moist environments.
Anthracnose is most common in overwatered Calatheas and specimens damaged by frost or cold. Typical symptoms include:
- Yellowing along the edges of the leaves – the yellow edges usually turn tan, then dark brown.
- Water-soaked brown spots with yellow halos appear on young foliage.
- Calathea stems may develop large cankers or lesions.
Treatment and Prevention of Anthracnose in Calatheas
Fortunately, Anthracnose is rarely fatal to Calathea plants. Still, avoid injuring or repotting your Calathea at this time.
- Remove severely infected foliage and dispose of it safely.
- Warm, arid conditions will slow infection spread. You can keep them dry by not misting, wetting, or splashing the leaves. Avoiding overhead watering can also be beneficial.
- Reduce the spread by increasing airflow through the leaves.
- Keep your Calathea healthy by spraying it with a copper-based fungicide once a week.
[4] Septoria Leaf Spot of Calatheas
The fungus septoria causes yellow spots on leaves and first appears as tiny wet light gray or tan marks on the undersides of your Calathea’s lowest and oldest leaves.
As the disease advances, the water-soaked patches typically turn brown. As with other leaf spot diseases, there are usually many spots rather than just a few lesions per leaf.
Both black and yellow outlines can be seen around the brown spots.
Additionally, because of the negative effect on photosynthesis that leaf damage has, the affected leaves typically turn yellow.
Septoria leaf spots develop and spread until they reach a critical size and kill the plant’s leaves.
Treatment and Prevention
Septoria spores typically spend the winter in the soil, debris, or dead plant matter. That is why proper sanitation and hygiene are critical.
Never handle your plant when it is wet, and permanently remove debris.
Improving air circulation and lowering humidity is critical to halting or slowing the spread of the Septoria fungus.
Fungicide sprays with copper are usually used to treat it. Spray your Calathea every week to ten days as needed.
[5] Powdery Mildew
Powdery mildew is a disease caused by fungi that makes the leaves of your Calathea look white and dusty.
Powdery mildew has arrived on your Calathea if you see white, powdery growths on new shoots, leaves, and other parts of the plant.
You may first notice the fungal problem on your Calathea plant when small, pale yellow spots appear on the leaves. Small spherical dusty spots will eventually form from the tiny spots.
White, fussy fungal growths will cover nearly all leaves as the disease progresses.
In addition, fungal spores can quickly jump from one healthy leaf or plant to the next if left untreated.
Calatheas severely infected by powdery mildew are often sluggish, develop abnormally short leaves, and may die.
Treatment and Control of Powdery Mildew in Calatheas
- Clean up your Calathea – Snip off infected leaves immediately and discard the debris. Always prune back to healthy tissues.
- Reduce humidity and improve airflow – Space, thin, and prune your Calathea accordingly to increase light penetration and air circulation. Remember, poor ventilation and high humidity favor this wind-borne pathogen.
- Chemical controls – I highly recommend spraying your Calathea with a sulfur-based fungicide (Amazon link) against powdery mildew.
[6] Nutrient Deficiency
Chlorosis, which results from nutrient deficiencies, is the most common cause of Calatheas’ yellowing and yellow spots.
It’s the time of year when leaves lose their green pigmentation and can no longer perform photosynthesis.
Insufficient magnesium, nitrogen, zinc, and iron levels are frequently observed in Calathea plants. Yellow spots on leaves are a typical result.
Water shortages often occur in tandem with nutrient deficiencies. For one thing, plants can’t take in soil nutrients without water.
A magnesium or zinc deficiency may be to blame if the leaves of your Calathea are clustered near the plant’s main stem or base.
Solution
- Feed your Calathea a well-balanced houseplant fertilizer that indicates your target nutrients on the label. For instance, you can apply Epsom salt (Amazon link) to correct magnesium deficiency.
- You can use compost to rejuvenate the soil.
- Relocate your Calathea to a brighter spot to boost nitrogen levels.
- Repotting your Calathea is an all-in-one solution for most nutrient deficiencies.
[7] Edema
Calatheas edema is typically caused by excessive moisture and low light conditions. A bacterial or fungal infection does not cause it.
Edema has an impact on the overall health of your Calathea. Wilting, drooping, and browning or yellowing of the leaves are all symptoms.
Calathea plants suffering from edema will also develop corky brownish-yellow or black spots on their leaves.
In addition, brown spots with a yellow halo will appear on infected leaves caused by burst tissue.
Solution
Overwatering is the cause of all edema cases. However, it is fixable by changing the cultural conditions and environment.
- Any infected leaves should be removed and discarded.
- Consider repotting your Calathea to provide the roots with a dry, water-free environment.
- Put your Calathea in a warm spot with bright, indirect light.
[8] Excess Light or Leaf Scorching
Calatheas, like all green plants, have chlorophyll, which is responsible for green pigmentation and photosynthesis.
When your Calathea receives too much light, it will develop leaf scorch. Typically, the chloroplasts (cells that produce chlorophyll) are damaged.
As a result, affected leaves turned yellow or were dotted with yellow spots.
Because of the magnifying effect of water droplets, chlorosis (loss of green pigment) is quite aggressive on wet leaves.
Solution
- Gradually introduce more light to your Calathea because the sudden movement can cause leaf scorch.
- Move your Calathea to a partially shaded location.
[9] Pest Infestation
Calathea plants are especially prone to getting spider mites. Mealybugs, thrips, aphids, white flies, and scale insects can also attack them.
Pest infestations can cause feeding areas to have stunted leaves and yellow spots.
The problem is usually terrible if your Calathea has been overwatered, weak, or not fed well.
How to Get Rid of Pests
- Mist your plant to prevent spider mites from reproducing.
- Use a strong jet of water to eliminate mealybugs and other bugs.
- It is also possible to use insecticidal soaps, neem oil, and horticultural oils. However, you must re-spray weekly until the infestation is eradicated.
[10] Low Humidity
Calathea plants like high humidity, just like most tropical plants. In low moisture, they will become stressed and develop yellow spots.
Low humidity is also indicated by drooping, wilting, and browning of leaf tips.
Solution
Calatheas evolved to live in areas with a humidity of 90% or higher. However, your houseplant can tolerate humidity of 50-70%.
You can boost humidity levels by:
- Using a humidifier.
- Misting (I don’t recommend this if your Calathea appears sickly)
- Making a humidity tray.
- Putting your plants in a group.
[11] Frost Damage
Calatheas are not frost-hardy. They will suffer cold damage if exposed to frost, cold drafts, or temperatures below 60°F (15°C).
Frost damage allows for fungal and bacterial infection. It also exacerbates the effects of poor lighting, edema, nutrient deficiencies, and overwatering.
The result is stunted growth, wilting, and yellow or brown spots on the leaves. Another symptom is leaf drop.
Solution
- Do not expose your Calathea to frost, cold drafts, or temperatures below 60°F (15°C).
- Water frost or cold-shocked Calatheas sparingly.
- Place a blanket or a steam vaporizer next to your Calathea.
[12] Inconsistent Watering
Allowing the soil to dry out and overwatering your Calathea will result in various problems, including root rot.
In addition, soggy soil conditions foster the growth of bacterial and fungal pathogens that cause yellow spots on leaves.
Inadequate watering exacerbates the effects of frost damage, edema, pest infestations, and light problems. These issues will cause yellow spots and a variety of other symptoms.
Solution
Water your Calatheas regularly to keep the soil evenly moist (but not wet). They dislike having wet feet.
[13] Fertilizer Burn
Calathea plants do not require a lot of fertilizer. However, too much fertilizer will result in brown or yellow spots, yellowing, and other problems.
In addition, fertilizer salts in excess will burn the roots, reducing water and nutrient absorption.
Solution
To remove excess fertilizer salts, flush the soil.
Apply a light dose of a well-balanced fertilizer at half the recommended strength as a preventative measure.
I only use it during the spring and summer growing seasons.
How to Prevent Yellow Spots on Calathea
- Maintain ideal temperatures between 70 and 90 degrees Fahrenheit (21-32 degrees Celsius).
- You can ensure adequate air circulation by spacing your plants, pruning some leaves, and using a small fan.
- Maintain consistent watering practices, keeping the soil moist but not soggy. Also, avoid wetting the leaves, overhead watering, and splashing.
- Adopt good hygiene and cultural practices – Remove plant debris immediately, avoid handling wet Calatheas, and sterilize cutting tools.
- With proper feeding and care, you can always keep your Calathea healthy.
- Provide a high humidity level of 50% to 100% (preferably 70%).
- Provide plenty of indirect, bright light.
- Ensure proper drainage.