White Spots On Oregano Leaves – Causes And Solutions

Oregano is an herb that belongs to the mint family or Lamiaceae. In the past, it was very popular in every meal of people in the Mediterranean region. After that, marjoram became more and more popular and became one of the indispensable spices in cuisines around the world.

People often use oregano in their diet as a supplement and a balm. In particular, oregano also contains antioxidants such as thymol, carvacrol, limonene, terpinene, ocimene, and caryophyllene. They create a characteristic, unique flavor and bring many health benefits to humans.

Oregano is effective in treating diseases such as ulcers, asthma, diarrhea, indigestion, and strengthening resistance. In addition, oregano is also effective in reducing inflammation, fighting bacteria, regulating blood sugar and lipids, and preventing cancer.

So many gardeners love to grow oregano in the garden or in pots to use for daily meals. However, white spots on oregano leaves will be one of the most common problems you face when growing this herb. Let’s learn about the causes and prevention of white spot disease of oregano.

White Spots On Oregano Leaves – What Is The Cause?

The spots that appear on the leaves of oregano can be brown, black, or yellow, and white. There are many reasons why white spots on plant leaves appear such as caterpillar waste, too much nitrogen in the soil, and fungal and insect diseases.

Caterpillar Waste

White spots on the leaves of oregano can be caused by the droppings of the caterpillars. This reason is absolutely nothing to worry about the health of the plant. You only need to clean the leaves and disinfect them before consuming them to avoid affecting the digestive system.

To determine the cause, you can wash the leaves with water. If the white, brown, or black spots are small and raised on the leaf surface, they are most likely caterpillar waste. They will be cleaned with water when you wash the leaves a few times.

However, the leaves of oregano are very thin and weak, if you use high-pressure water, it will damage the leaves and affect the yield of this herb. Therefore, to prevent moth waste, you should use a net or a trellis to limit the contact between the caterpillar and the leaves of oregano.

white spots on oregano leaves

Too Much Nitrogen In The Soil

One of the other common causes for white or yellow spots to appear on the leaves of oregano is too much nitrogen in the soil. As you know, nitrogen is an essential mineral for the growth of plants, especially leaves. However, if you fertilize with too much nitrogen, the leaves will be damaged very easily.

The first sign that you may see is yellow or milky spots on the leaves. The color of the spot will blend and change with each degree. These spots will spread to the entire leaf and stem if the damage becomes more severe.

To remedy this situation, you need to stop fertilizing to remove excess nitrogen from the soil. Alternatively, you can also wash the soil with water to remove nitrogen from the soil. However, you need to make sure that the soil drains well, especially while you’re growing oregano in a pot. If the soil does not drain well, soil washing will cause waterlogging and root rot. After you remove excess nitrogen from the soil, oregano will need a short time to recover and become healthy again.

Fungal Diseases That Cause White Spots On Oregano Leaves

Fungal diseases are one of the most common causes of white, yellow, brown, or black spots on the leaves of oregano. Although fungal diseases are diverse and different, they share many similarities in terms of treatment and prevention.

Fungal diseases occur mainly due to humid environments, poorly drained soil, and poor air circulation. A humid environment is ideal for fungi to grow and attack plants. Overwatering will cause root rot, which causes the fungus to multiply faster under these conditions. In particular, fungal spores can also appear in the air and attach to leaves on contact or through open wounds on leaves.

Therefore, to eliminate and prevent fungal diseases, you should keep oregano in a dry environment. Some of the measures you can take are as follows:

  • Do not overwater to cause waterlogging.
  • The soil drains well, especially if you grow oregano in a pot.
  • Do not water the leaves at night.
  • Make sure the oregano is dry at night.
  • Use clean scissors to prune the branches, avoiding creating too many open wounds for the fungus to attack.
  • Water only when the ground is 1-2 inches dry.
  • Place the pot in a place that receives daily sun and good air circulation when you grow oregano in a pot.
  • Eliminate overhead foliage, vines, and weeds when growing marjoram in the garden.

Rust Causes Spots On Oregano Leaves

Oregano is very susceptible to rust and spots appear on the leaves. The color of these spots can range from white, brown, yellow, or orange. Orange spots are the most recognizable sign of this fungus because they do not appear in common mushrooms. Rust will spread very quickly and is difficult to treat. After the spots appear, the rest of the plant will wilt and die. The best thing you can do to prevent the spread of the fungus is to remove diseased plants or a surrounding clump.

Pests And Insects

Pests and insects are also another common cause of white, brown, or yellow spots on leaves. Oregano will face 3 common insects such as aphids, thrips, and spiders. These insects will attack the leaves directly and create holes in the leaves or spots because they inject toxins into the leaves of oregano.

Aphids are the biggest enemy of many gardeners and it is very difficult to completely destroy them. They are small yellow or green insects that love to eat oregano leaves. Aphids often cause yellowish-white or brown spots on the leaves. They can spread quickly and destroy the entire plant area if you do not detect and handle them in time. To get rid of this insect, you can set traps, use neem oil or orange oil to mist daily, and prevent eggs from hatching.

Thrips are also common insects that attack oregano and leave spots on the leaves. Not only do they attack, but they can also transmit oregano viruses. Therefore, you need to get rid of them by applying neem oil and cleaning the leaves. In particular, you should also avoid planting oregano near other plants that thrips love, such as onions and garlic.

Spider mites can also attack oregano and leave yellow spots on the leaves or white patches. They thrive in dry and dusty environments. So, to get rid of this insect, you need to maintain the ideal humidity with a humidifier, mist daily, or use a cobblestone tray. To kill Spider mites, you can use orange oil or peppermint spray to kill them and prevent the eggs from hatching.


The white spots that appear on the leaves of oregano can be related to various causes such as caterpillar waste, excess nitrogen in the soil, fungal diseases, rust, or insect attack.

The spots on the leaves can be a mixture of different colors because oregano suffers from many different diseases. However, if white spots appear on the leaves that can be washed off with water, you can still consume normal oregano. However, if the spots are milky white, yellowish white, or a mix of black and brown then you should not consume them.

To get rid of leaf spots, you need to pinpoint the exact cause and find an effective remedy. You can also use neem oil, orange oil, or peppermint oil to sanitize the leaves, kill insects, and prevent eggs from hatching.

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