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If you notice white spots on your plant leaves, it could be powdery mildew. Learn what this disease is and how to treat it!

 Has your plant been having some trouble lately? Are you seeing white spots on the leaves? If so, you may be dealing with a case of powdery mildew. Powdery mildew is a common fungus that affects many types of plants, and it can cause serious damage if left untreated.

In this post, we'll discuss what powdery mildew is, how to identify it, and how to treat it. Keep reading to learn more!

White spots on plant leaves

White spots on plant leaves can be caused by a number of things, but one of the most common culprits is powdery mildew. Other causes include nutrient deficiencies, pests, diseases, etc. White spots are also common in plants that are stressed or have been damaged.

High humidity and poor air circulation are also causes of white spots. Planting your vegetation without adequate spacing where it cannot get proper air circulation, or overwatering your garden or potting soil can create prime conditions for white spots to grow.

Are white spots on plant leaves a sign of powdery mildew?

When you see white spots on plant leaves, it's usually a sign of powdery mildew. Powdery mildew is caused by a type of fungus that grows on the surface of the leaves. The fungus feeds on the juices in the leaves, and it can cause the leaves to turn yellow or brown. 

The fungus also produces a white, powdery substance that can be seen on the leaves. This is what gives powdery mildew its name.

What is powdery mildew?

 

 Powdery mildew is a fungal disease that affects plants. When the fungus takes hold of one of your plants, a layer of mildew made up of many spores develops over the leaves. The powdery mildew spores are then carried to other plants by the wind. Powdery mildew can stifle plant growth and, if severe enough, reduce fruit quantity and yield.

Powdery mildew has  different species, each of which attacks a variety of different plants in the garden, for example Cucurbits (squash, pumpkins, cucumbers, melons), nightshades (tomatoes, eggplants, peppers).

Causes of powdery mildew

Powdery mildew is typically caused by one of three different fungi: Sphaerotheca pannosa, Oidium neolycopersici, or Podosphaera xanthii.

  • Sphaerotheca pannosa is the most common type of powdery mildew. It attacks a wide range of plants in the cucurbit and nightshade families.
  • Oidium neolycopersici is a powdery mildew fungus that attacks tomato plants.
  • Podosphaera xanthii affects cucurbits, such as squash, pumpkins, and cucumbers.

How to identify powdery mildew

Powdery mildew can be tricky to identify because it often looks like other types of plant diseases. If you're not sure whether your plant has powdery mildew, take a close look at the following points:

  • Plants Affected by Powdery Mildew Appear to Have Been Dusted with Flour
  • Powdery mildew, like any other type of fungus, begins as circular, powdery white spots that may appear on leaves, stems, and occasionally fruit.
  • Powdery mildew may affect the entire leaf surface, but it typically affects the top half.
  • The most vulnerable stage is when the plant is young. The leaves become yellow and crispy.
  • The fungus may cause certain leaves to curl, break, or get damaged.
  • Powdery mildew will spread over the leaves or the afflicted regions of the plant, resulting in white spots that cover a large portion of them.
  • The leaves, buds, and budding tips will also suffer damage. These symptoms are most frequently observed in the late growing season.

How to control powdery mildew

When plants are severely infested with whiteflies it's impossible to cure them. Instead, concentrate on how to prevent powdery mildew from spreading. Remove and destroy any infected foliage, stems, and fruit; either by discarding them in the garbage or burning them. Any diseased plants or fruit trees should not be composted since the illness may be carried by the wind.

Never set pruning shears to contact healthy plants or leaves after trimming away portions of the heavily infected plant. Rubbing alcohol should be used to clean your scissors first.

Homemade prevention

Sulfur, lime-sulfur, neem oil, and potassium bicarbonate are all good organic fungicides to get rid of powdery mildew. These work best when used before the fungal diseases strikes or before you first notice any symptoms of it.

Many of these remedies include baking soda. Just be aware that baking soda can burn entire plant and it can build up in your soil, potentially causing deficiencies in calcium, magnesium, and iron. Potassium bicarbonate can be substituted for baking soda. Test these sprays on a small area first to make sure they do not damage your plants.

  • Mix 1 tablespoon baking soda with 1 tablespoon vegetable oil and 1 teaspoon liquid soap in 1 gallon of water.
  • Mix 4 tablespoons baking soda with 2 tablespoons of Murphy's oil soap in 1 gallon of water.
  • Mix 2 to 3 tablespoons of vinegar with 1 gallon of water. Be sure to test this first because vinegar can burn plants.
  • Neem is an organic fungicide. Follow instructions on the label.
  • Mix 1 part milk with 10 parts water.
  • Some folks swear by mouthwash as an effective fungicide but it is not organic. They recommend 1 cup mouthwash to 3 cups of water.

Treating powdery mildew can be a difficult task. However, another efficient house treatment is milk spray. Spray roses with diluted milk (typically 1:10) as a preventative measure or on the first sign of infection. Re-apply every seven to ten days as needed. Some gardeners use milk exclusively, while others mix it with other organic fungicides such as baking soda or vinegar.

Insects that cause white spots on plants

 

There are several types of insects that can cause white spots or other discoloration on plant leaves. These include mealybugs, scale, and aphids. All of these insect pests feed on plant sap, and they excrete a sticky substance called honeydew. This honeydew can attract sooty mold fungi, which then causes the leaves to appear black.

 

Mealybugs

Mealybugs are small, white insects that can be found in clusters on the undersides of leaves, stems, and flowers. They suck plant sap and excrete honeydew, which can lead to sooty mold growth.

Scale

Scales are small, hard-bodied insects that attach themselves to plant stems and leaves. They also suck plant sap and excrete honeydew, which can lead to sooty mold growth.

Aphids

Aphids are small, soft-bodied insects that feed on plant sap. They come in a variety of colors, but they are often green or black. Aphids also excrete honeydew, which can lead to sooty mold growth.

Other potential causes of white spots on leaves

1. Sunburn

Leaves can get sunburned if they are exposed to too much direct sunlight. The leaves will turn white or yellow and may eventually brown and die.

If the spots are on the side of the leaves that face the sun, it's likely due to sunburn. You can try moving the plant to a shadier spot or providing some shading for it. If the damage is severe, you may need to remove and dispose of the affected leaves.

2. Chemical Burn

Leaves can also get chemical burns from herbicides, pesticides, or other chemicals. These burns will typically appear as white or yellow spots on the leaves.

If you recently applied any herbicides, pesticides, or other chemicals to your indoor plants or outdoor plants, it's possible that they were damaged by a chemical burn. You can try washing the leaves with water to remove the chemicals. If the damage is severe, you may need to remove and dispose of the affected leaves.

3. Water stress

Plants can also develop white spots when they don't get enough water. The leaves will turn white or yellow and may eventually turn brown and die.

If the spots are on the tips or edges of the leaves, it's likely due to water stress. You can try watering the plant more frequently or deeply. If the damage is severe, you may need to remove and dispose of the affected leaves.

4. Nutrient deficiency

Plants can also develop white spots when they're lacking in nutrients, such as nitrogen, phosphorus, or potassium. The affected leaves will typically be small and pale green or yellow in color. As the deficiency worsens, the leaves will turn brown and die.

If the spots are on new growth or on the tips and edges of leaves, it's likely due to a nutrient deficiency. The affected leaves will typically be small and pale green or yellow in color.

You can try fertilizing the plant with a nitrogen-rich fertilizer. If the damage is severe, you may need to remove and dispose of the affected leaves.

5. Bacterial leaf spot

Bacterial leaf spot is a type of plant disease that can cause white spots on leaves. The bacteria infect the plant through wounds in the leaves, and they multiply rapidly in warm, wet conditions. The spots can eventually turn brown and kill the leaves.

If the spots are circular or irregular in shape, it's likely due to bacterial leaf spot. The spots can also have a yellow or brown halo around them.

You should remove and dispose of the affected leaves immediately. You can also try spraying the plant with a copper-based fungicide or bactericide. However, it's important to note that these products may not be effective against all types of bacteria.

6. Diseases

There are many different types of plant diseases that can cause white spots on leaves. Some common examples include powdery mildew, leaf spot, and rust. These diseases are caused by fungi, bacteria, or viruses, and they can spread quickly in warm, wet conditions.

If the spots are irregular in shape or have a fuzzy appearance, it's likely due to a disease. The affected leaves may also be discolored or have raised bumps.

If you suspect that the white spots on your plants are due to a disease, you should remove and dispose of the affected leaves immediately. You can also try spraying the plant with a spray bottle. However, it's important to note that these products may not be effective against all types of diseases.

Takeaway

As you can see, there are many different causes of white spots on plants. If you're unsure what is causing the spots on your plants, it's best to consult with a professional. A professional can help you identify the cause and determine the best course of treatment. Thanks for reading!

1 comment

  • My honeysuckle trumpet vine develops white spot every year on leaves as well as the buds. Before attempting to bloom, it is covered in a fuzzy white matter and a black substance. I have done everything that I have researched to do, but it happens every year. Help!
    Thanks!

    Vicki

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