What Causes White Spots on Plant Leaves & How to Treat Them?

When growing plants, you may notice white spots on plant leaves. These tiny white spots on plant leaves can be frustrating, but don't worry, there may be white spots on plant leaves not mildew. 

They can be caused by a fungal or bacterial infection, poor nutrition, or small insects, and can be treated with some simple methods. In this comprehensive guide, we'll help you find what causes the white spots on plant leaves and how to get rid of white spots on plant leaves.

Main Content:

• 1. What Causes the White Spots on Plant Leaves?
• 2. How to Get Rid of White Spots on Plants
• 3. Conclusion
• 4. FAQ about White Spots on Plant Leaves

What Causes the White Spots on Plant Leaves?

White spots on plant leaves can be caused by pests, diseases, or nutritional deficiencies. This includes powdery mildew, spider mites, calcium or magnesium deficiencies, edema, chemical damage from pesticides or herbicides, and certain viral infections.

Timely diagnosis and treatment of white spots on plant leaves are essential for plant health and growth. So let’s move to the first main reason for white specks on plant leaves: plant disease.

Plant Disease

White spots on plant leaves can be caused by various diseases, including fungal and viral infections. Powdery mildew is the most common among them, due to its airborne fungal pathogens that can affect a wide range of plants.

Powdery Mildew

Powdery mildew is a common fungal disease characterized by white, powdery spots on leaves, stems, and buds, resembling flour dusted on the surface. The disease spreads quickly in warm (60-80°F) and dry environments.

Downy Mildew

Downy mildew is a fungal disease that thrives in cool (58-78°F) and humid (humidity >85%) conditions. It typically appears as white or grayish mold on the undersides of leaves, sometimes causing yellow spots on the upper surface of the leaves.

Compared to powdery mildew, downy mildew is more destructive. If left untreated, downy mildew can cause severe damage to crops and can kill all plants within a week. It is therefore necessary to remove the infected leaves immediately and carry out the treatment mentioned in the latter part of this article.

Whether it's powdery mildew, downy mildew, or other infections for white specks on plant leaves, prevention is key. Powdery mildew and downy mildew can be effectively prevented by maintaining good air circulation, proper humidity, and temperature with full-spectrum grow lights and grow fans.

Downy Mildew vs Powdery Mildew

Bacterial Infection

The primary bacterial infections that cause white spots on plant leaves are as follows:

Bacterial Leaf Spot

Bacterial leaf spot infections are caused by high humidity, warm temperatures, and dense planting. This disease results in water-soaked spots on the leaves, which initially appear dark green and then turn white or yellow. These spots may also be surrounded by yellow halos.

Bacterial Wilt

Bacterial Wilt infections occur due to warm and humid conditions, root or stem damage, and contaminated soil. Bacterial Wilt Symptoms include leaves starting to turn white or yellow-white from the edges, gradually spreading across the entire leaf, and eventually leading to wilting of the leaves and the whole plant.

Bacterial Streak

Bacterial Streak infections are primarily caused by high humidity, wind and rain spreading the bacteria, and infected seeds. The symptoms include the formation of white or light yellow streak-like spots on the leaves. These spots often merge, leading to large areas of discoloration and leaf wilting.

By being aware of these bacterial infections causing white specks on plant leaves, you can take preventative measures to protect your plants and maintain a healthy garden.

Pests

Plants are often attracted to white spots on plant leaves bugs due to factors like high humidity, warm temperatures, over-fertilization, and overcrowded planting. The appearance of these white spots on plant leaves bugs are listed below:

• Spider Mites: Spider mites are minuscule and difficult to spot, typically in red, yellow, or green colors. These tiny pests survive by extracting plant sap, which leads to yellow or white marks on the leaves and the frequent presence of delicate webs on the plants.
• Aphids: Aphids are small, soft-bodied insects in various colors such as green, yellow, black, red, or brown. They feed on plant sap, resulting in white spots or discoloration on the leaves. Their release of honeydew can attract other pests or lead to mold growth.
• Whiteflies: Whiteflies are small, white insects with wings covered in a white, powdery substance. These tiny white flying insects feed on plant sap, causing white spots or discolored areas on the leaves.
• Thrips: Thrips are slender and small, ranging in color from yellow to brown. They pierce the surface of leaves to feed on sap, resulting in white or silvery spots or streaks on the leaves.
• Leaf Miners: Leaf miners' larvae are tiny, maggot-like creatures, while the adults are usually small beetles. The larvae tunnel inside the leaves, creating white, winding, tunnel-like marks.

You can identify these pests by closely examining the spots, streaks, webbing, and the appearance of the pests on the plants. Using a magnifying glass can help you see these tiny pests more clearly.

Whiteflies on plants

Nutrient Deficiency

White spots on plant leaves may also be due to various nutrient deficiencies. Here are some possible nutrient deficiencies that can cause white marks on leaves:

• Calcium Deficiency: When calcium is deficient, new leaves and growth points develop white or yellow spots, and leaf tips and edges may start to wilt. In severe cases, the growth point of the plant may die. 
• Magnesium Deficiency: Magnesium deficiency causes leaf chlorosis in older leaves, with the veins remaining green. White spots or blotches may appear on the leaves, and eventually, the entire leaf may turn yellow-white.
• Sulfur Deficiency: Sulfur deficiency results in the entire leaf turning yellow, and in severe cases, new leaves may turn yellow-white with white spots or blotches.

These nutrient deficiencies can result from a lack of specific nutrients in the soil, inappropriate soil pH or unbalanced fertilization. Now that you know what are white spots on plant leaves, let's take some simple methods to help your plants recover their health quickly.

How to Get Rid of White Spots on Plants

Once infected with white spots on plant leaves, whether it's downy mildew, powdery mildew or white spots on plant leaves not mildew, it’s challenging to completely eradicate. Therefore, for gardeners, the focus should be on prevention rather than treatment, such as choosing disease-resistant plant seeds.

If unfortunately your plants are infected with white spots, follow the solution below and then quickly fix the diseased plant.

How to Get Rid of White Fungus on Plants?

If you find white specks on plant leaves caused by fungus like powdery mildew or downy mildew, start by removing the infected leaves, branches, flowers, or fruits to prevent the spread of the fungus. In severe cases, you may need to remove the entire plant to safeguard the rest of the garden.

Ensure good air circulation by supporting plants and/or selective pruning, and water in the early morning so plants dry out during the day. It's important to maintain relatively low humidity around the plants. 

Also, avoid overcrowding, overwatering, and poorly drained soil. For the same reasons, remove weeds. If you are growing indoor plants, use Medicgrow grow tent kits to maintain relatively low humidity and appropriate light intensity.

You can use fungicides targeted at downy mildew and powdery mildew. I recommend neem oil and copper or phosphorus-based fungicides as they are quite effective. White vinegar and a mixture of soap water and alcohol can also be used as a treatment. The key is to apply it every evening on the infected plants.

white spots on plants

How to Cure White Spots on Plant Leaves Not Mildew?

White spots on plant leaves not mildew could be due to pest infestations, nutrient deficiencies, or environmental factors. Common pests include spider mites, aphids, and thrips. 

Treatment methods include rinsing plants with water, using insecticidal soap or neem oil, and introducing beneficial predators like predatory mites, ladybugs, lacewings, and hoverflies.

Nutrient deficiencies such as a lack of calcium, magnesium, and zinc can also lead to white spots. These issues can be fixed by applying soil additives or foliar sprays with the corresponding nutrients and adjusting the soil pH.

Additionally, environmental factors like sunburn or water stress can cause white spots. Place the plant in a well-lit but not overly scorched location. Keep the soil evenly moist, increase watering during the growing season, and reduce watering during dormancy to prevent waterlogging.

For indoor plant growers, we suggest LED grow lights especially grow lights with timers like Medicgrow Spectrum-Y. These grow lights can control light duration and intensity to create the optimal environment for plant growth.

Conclusion

In conclusion, it's not difficult to deal with white spots on leaves, but the key is to prevent them. Sometimes it can be too late once the white spots on plant leaves appear. Adjusting the plant's growing environment we mentioned above using grow fans or UV grow lights can effectively keep plant leaves free of white spots.

FAQ about White Spots on Plant Leaves

1. What Are White Spots on Loropetalum Leaves?

White spots on Loropetalum leaves can be caused by various factors. Here are 3 common causes:

• Fungal Infections: Diseases like powdery mildew or leaf spot fungi can cause white spots on Loropetalum leaves. Powdery mildew appears as a white powdery coating on the leaves, while leaf spot fungi create small white spots that may enlarge over time.
• Pests: Insects such as spider mites or scale insects can feed on Loropetalum leaves, causing small white or yellow spots where they pierce the leaf surface and suck sap.
• Environmental Stress: Factors like excessive sun exposure, high temperatures, or poor air circulation can stress Loropetalum plants, leading to white spots on leaves as a symptom of stress or damage.

To properly diagnose and treat white spots on Loropetalum leaves, it's important to inspect the plants closely and identify the underlying cause. Treatment may involve improving growing conditions, and using appropriate fungicides or insecticides if necessary.

2. What Causes White Spots on Tomato Leaves?

White spots on tomato leaves can be attributed to various factors including fungal diseases like powdery mildew, bacterial infections such as bacterial spots, viral diseases, and pest infestations like whiteflies and spider mites.

In addition, improper irrigation practices, such as over-irrigation or poorly maintained drip irrigation systems, may result in tomato leaves remaining wet for long periods, creating favorable conditions for fungal and bacterial growth.

3. What Are White Spots on Cucumber Leaves?

White spots on cucumber leaves may be caused by low relative humidity, which favors the growth of powdery mildew and red spiders. For low relative humidity around cucumber, spraying devices can be installed to maintain high relative humidity while avoiding flooding cucumber roots.

In addition, fumigants should be applied to prepared soil seedbeds 2-4 weeks before cucumber planting. Use foil and other reflective mulches to repel virus-transmitting aphids in autumn-planted cucumbers.

Potassium also enhances disease resistance in cucumbers, and foliar sprays of potassium salt solutions have been shown to control powdery mildew on cucumber leaves.

Read also: Why Are My Cucumber Leaves Turning Yellow?