A healthy mint is fresh and green to look at. However, you might notice your mint covered with white spots. A lot of factors are responsible for causing white spots on your mint leaves.
Let us look at each of them below with the treatment required.
Fungal diseases are one of the most common causes of white spots on mint leaves. Most of the fungi have a similar mechanism.
Powdery mildew develops when a biotrophic fungus starts to feed on the mint leaves of your plant. It causes white spots with a texture not unlike sprinkled flour.
It is often mistaken for dirt or dust, more so when it is still greyish in colour in the early stages.
Powdery mildew develops when the mint is in a place with a dry condition. Spores are formed in high humidity, while low humidity propels the spread of these spores.
Once the leaves of the mint dry out, this fungus begins to form on the surface of the leaves, known as powdery mildew.
This disease is easy to recognize. The affected leaves turn yellow and then white with the powdery substance. This disease can cover the entire plant in mildew.
The severity will depend on how long the disease has been left untreated.
Powdery mildew attacks the lower leaves first and then makes it’s way up. If not treated at the earliest, it can cover the entire plant.
Rust is a common disease for the mint plant. White rust is very similar to rust with respect to its properties, except for the white colour of the spots.
The bumpy, white spots develop early on. White rust usually happens because of high humidity. The causes of the development of white rust include overwatering and dense planting of the plants.
A lot of fungicides are available in the market to treat the fungus on your plants. Different fungi will have different requirements.
Don’t plant your plants too close together. Make sure there is enough space between the plants for proper aeration.
Do not overwater your plant. Humidity is one of the main causes of fungal infections.
Fungus is usually contagious, so make sure you isolate the plant as soon as you spot any signs of fungus.
Mint plants are prone to a lot of viral infections.
A group of viruses called the mosaic viruses to leave a pattern of leaf spots on plants. These viruses attack a lot of plants species. They are a mosaic of several colours, such as green, yellow, white, etc.
This discolouration of leaves can lead to chloroplast disintegration. Chloroplasts are tiny, green bodies present in the leaves that help to convert sunlight into energy that helps the plant grow well.
Chloroplast disintegration leads to the leaves losing their colour and turning pale.
There are many virus strains present in the atmosphere, and it is difficult to know exactly which one attacked your plant.
Some of the most common virus strains that leave white spots are Tobacco Ringspot Virus (TRSV), Cucumber Mosaic Virus (CMV), and the Tomato Aspermy Virus (TAV).
Some of the pests that transmit these viruses include aphids, whiteflies, nematodes, and thrips.
A mint root can already be infected with a virus even before it has been planted. Viruses can also be easily transmitted by using unclean tools or improperly disposing of diseased plants.
There is no treatment for viral diseases. The best way to get rid of them is to cut off the affected parts with pruning shears. Make sure you clean the tools thoroughly before and after using them.
Check all the other plants to see if they are safe. Your mint might have been affected by some other plant, or your affected mint might have spread the virus to the other plants.
If your plant is severely damaged, you will need to dispose of the entire plant. Wrap it in a paper bag and throw it into the garbage bin immediately. You can also burn the infected plant outside the house.
Make sure you do not leave any remains. Get rid of the soil your plant was growing in, as well as the container it was planted in.
It is not just the fungal or viral infections, your mint can be infected by pests as well that can cause the white spots. Let us look at a few of them below.
Spider mites get their name from spiders, owing to the eight legs and a waxy abdomen that helps them move around better. They belong to the arachnid family and are related to spiders, scorpions and ticks.
Spider mites suck the juice out of your leaves and leave little holes all over. Female spider mites breed on the underside of the leaves, making them hard to spot. They also hide along the veins of the leaves.
As the spider mites suck out the chlorophyll, they leave white spots that resemble dust. They also make webs on the leaves, leaving a white trail all over the plant.
It is not a huge cause of concern if you find a small number of spider mites. However, if it is a large colony, you will need to get rid of them as soon as possible, as an attack by a large colony can result in the death of the plant.
Spider mites thrive during the warmer months, breeding in high temperatures and humidity. Your plant is usually safe during winters.
Whiteflies and mealybugs
Whiteflies and mealybugs have a lot in common. Both these pests of the mint plant, create white matter on your plant. Whiteflies and mealybugs suck out the juices out of the mint, just like spider mites.
Without chlorophyll, the plant becomes too weak and cannot process photosynthesis. This results in pale spots all over the mint plant.
Mealybugs and whiteflies leave a mass of white fluff on the underside of leaves, containing their eggs. They reproduce at a very quick rate, making them a nuisance for mint plants.
If the pest infestation is on a small scale, you can wash it off with water. Make sure your plant can handle a strong stream of water. Some pests tend to feed on the younger plants, which are too fragile to withstand a strong jet of water.
In that case, you can use insecticidal soap on the plant.
Neem oil is a great alternative to get rid of most pests. Dilute your oil with water and spray the entire plant early in the morning about twice a week for 3 to 4 weeks.
To get rid of mites, you can introduce favourable insects like ladybugs which feed on them.
Lack of nutrition is also sometimes responsible for white spots on mint leaves.
Iron chlorosis and manganese deficit
Iron is very important for the production of chlorophyll and enzymes. Without chlorophyll, there will be no green colour in the plants, which results in chlorosis. A lot of processes that happen in the mint plant depend on this.
If the main vein of the leaf is green, but the rest of the leaf is white in colour, your plant is clearly suffering from iron chlorosis.
A deficit of manganese is also related to a lack of iron. Manganese is important in the process of photosynthesis.
Lack of manganese can be spotted in newer growth because of its immobility through the plant.
The iron deficit is usually caused due to mismanagement of soil, and the manganese deficit is connected to the iron deficit.
Magnesium is necessary to capture energy from the sun for the process of photosynthesis. If magnesium is lacking in plants, the plant will wilt and the older leaves become dotted with white.
Improving the drainage of your soil can help with the iron deficit. When the soil has good drainage, the roots can absorb the metals easily.
Iron transmissions can be disturbed because of phosphorous-rich fertilizers as well. Make sure that the phosphorous in an NPK fertilizer is low while dealing with an iron deficit.
If you want to fix the magnesium deficit in the soil, get an NPK fertilizer that is lower in potassium, and one that is rich in magnesium nitrate.
Hard water and overwatering
Overwatering a mint plant can cause a nutrient deficiency in the soil. This leads to white spots all over the leaves of the mint.
Hard water relates to the quality of the water used on your plants. The mint intakes all the minerals from the water, the good and the bad.
Using hard water can result in the accumulation of white limescale.
Hard water means water that is heavy in calcium. Therefore, when the water evaporates, deposits of calcium are left on the surface of the leaves.
Clean your plant with a solution of vinegar and rainwater by washing the leaves gently with a sponge or a soft cloth.
As a long-term solution, get better quality of water. Try to use rainwater or melted snow, if possible, to water your plant.
Dust on leaves
Sometimes, it is just dust that has been gathered on your mint leaves.
Not cleaning regularly or not paying attention to your plant for a while can cause dust to settle on the mint leaves, looking like white spots.
While dust is the most harmless reason that causes white spots on your mint, do make sure to clean it quickly, as it can prevent the plant from getting enough sunlight and cause weakened growth.
Wipe the leaves of your plant clean with a damp cloth or spray it with lukewarm water. You can also use a dust brush if you can be gentle.
Is it safe to eat mint leaves with white spots on them?
It might not seem like it, but most of the time, it is safe to eat mint leaves with white spots on them.
If the white spots are due to bug damage, the mint leaves might be lacking in flavour, but as long as there aren’t any bugs currently on the leaves, they are edible.
In case, you do not want to lose on the flavour, you will need to wait for the plant to completely heal first.
If your leaves have white spots due to powdery mildew, the mildew should be cleaned off first. There won’t be any problems like feeling sick or the risk of dying from the consumption of such leaves.
The most that can happen is a mild stomach ache, but that is also avoidable if you clean off the leaves properly using the mentioned methods.
Just like due to bugs, mint will lose flavour because of powdery mildew as well.