How to Get Rid of White Spots on Mint (Causes and Treatment)


Indoor potted Mint plant leaves have white spots

Who doesn’t love the smell and the looks of a healthy mint? Sometimes that exterior can be ruined by white spots on leaves and stems.

White spots on Mint plant leaves can be caused by biotic and abiotic agents. Biotic agents include fungal diseases, viral diseases, and Pest infestations. Also, abiotic factors like Improper nutrition, hard water, dust on leaves can also be equally responsible for this issue.

If your mints are having this problem then you need to find out the causes to ensure correct treatment. I will discuss causes for these white spots, who’s at fault for creating them, and how to successfully get rid of them.

Causes of White Spots on Mint 

Fungal Diseases

I’ll start the list with fungal infections on mint. They’re one of the most common causes for white spots, at least in my experience. The majority of fungus have a similar mechanism. They penetrate the plant with hyphae, which are a needle-like fungus organ.

The primary purpose of hyphae is to stop all nutrition and water from coming to the plant and greedily transferring them to the fungus. I will feature two fungal diseases on this list, powdery mildew, sclerotium rot, and white mint rust.

Powdery Mildew

If you’re a long-time gardener, chances are you’re already familiar with this disease. Unfortunately, it’s frequent in high humidity and warm areas. The disease manifests on the leaves, and it’s easily recognizable. Small chlorotic, yellowish patches turn white after a while on the affected plant’s leaves.

It can even affect all foliage and cover it entirely in white-to-gray ash. The severity depends on how long the disease has been left untreated.

Powdery mildew affects lower leaves first and climbs its way up to the top. However, that doesn’t mean that the stem can’t be affected. If it’s left unchecked, it can cover up the entire plant. Wooly aphids, which we’ll discuss more later, can sometimes be vectors or transmitters of this disease.

Spores are formed in the presence of high humidity. Low humidity promotes quicker dispersal of these spores. These conditions are easily met in the spring and fall when the difference between the day and night temperature is considerable. Powdery mildew spores like average temperatures, between 70 and 80°F (21 to 26° C).

How to Treat It?

Conventional treatments include dusting with wettable sulfur or using copper-based fungicides. Wettable sulfur is also used as a fungicide. To apply it, you need to mix it with water according to the instructions on the package and spray it with a pressure sprayer.

Spray fungicide once every 7 to 14 days. The disease should be gone within 6 treatments. You can dust it over your mint in the early stages of disease development. They can be used preventively and curatively for powdery mildew.

Ecological treatments include using organic copper, and even milk! You can mix organic or whole milk mixed with water in a 1:1 ratio. It’s most effective when the infection first shows.

Organic copper is used the same way as sulfur, usually applied with a pressure sprayer. Important note: copper is toxic to fishes, so don’t use it near aquariums. Here are some copper-based fungicides that are safe to use:

Name of The FungicideAmountAmount of Water
Bonide 811 Copper 4E Fungicide1-4 tablespoons (.05-2.0 fl oz)1 gallon of water
Garden Safe Brand Fungicide32 tablespoons (1 fl oz) 1 gallon of water
Southern Ag – Liquid Copper Fungicide3-4 tablespoons1 gallon of water

White rust

Rust is another fungal disease that’s common when cultivating mint. As the name suggests, white rust has similar properties and symptoms to ordinary rust, except for the white spots. These spots grow in the subcuticular layer, meaning the fungi are hiding beneath the surface.

You can notice these bumpy, white spots in the early development of the disease. Overwatering and dense planting bolster white rust expansion. Both of these things have one thing in common, and that’s a high level of humidity.

How to Treat It

Firstly, don’t plant your mints too close to each other. I recommend at least one feet (29 cm) spacing between the plants.

Mint spreads its leaves horizontally, so it needs a lot of free space. Secondly, don’t overwater your mint. Make sure you keep track of the humidity. Chemical treatment involves fungicides, especially those based on azoxystrobin.

Chances to get rid of this disease skyrocket if you rotate it with a myclobutanil fungicide. Both products are great for treatment, and fungi are less liable to develop resistance to them.

Sclerotinia Rot

Chances are, you won’t meet this disease as often as the previous two. Sclerotinia rot or white mold stem rot has the exact mechanism as other fungi. It can infect your plant at any growth stage, although it prefers juvenile leaves and yummy stems. 

You can recognize it by its cotton-like mycelium mass that produces spores. It’s very active in the spring, so you’ll be quick to notice it.

In addition to the white dots, it penetrates your plant’s stem and leaves a sclerotium. This organ ensures survival throughout the winter, only to infect your plants in the upcoming spring.

How to Treat It

The main issue with sclerotinia is that it likes to wander from one plant to another. I know that growing tomatoes indoors is fun, but keep them away from your mint.

This fungus attacks various other vegetables (carrots, tomatoes, beans) and flowers (delphinium, dahlia), so check all other plants if you have them. As for the diseased plants, unfortunately, it’s best to get rid of them as soon as possible.

A study proved that spraying fungicides based on vinclozolin, copper, and thiophanate methyl were very effective in inhibiting further growth of sclerotinia rot.

These treatments are efficient to use when dealing with greenhouse cultivation. I still recommend the non-chemical treatment for the indoor cultivation of mint. In my humble opinion, it’s a simpler, cheaper, and eco-friendlier solution.

Viral Infections

Mint plants are prone to various viral infections. A unique group of viruses, called mosaic viruses, leave a recognizable pattern of leaf spots.

They can infect numerous plant species, and mint is not an exception. Mosaic comes as a palette of several colors, including dark-green, white, yellow, and bright green dots.

Discoloration of leaves leads to chloroplast disintegration. Chloroplasts are little green bodies on the surface of the leaves.

They enable your plant to convert sunlight into energy, making it grow strong and happy. By destroying these bodies, your mint loses its color and becomes pale.

Viral diseases don’t use the plant’s digestive system to take food and water. Their mission is to destroy cells and use their DNA to create more viruses.

There are many virus strains, and it’s hard to determine which one attacked your mint. Today, we know that the most common strains that leave white spots include the Tobacco ringspot virus (TRSV), Cucumber mosaic virus (CMV), and the Tomato aspermy virus (TAV).

Don’t let the names fool you! These names were given by the plant they were first discovered on, but they attack all kinds of vegetables, fruits, and flowers.

There are many distinct mosaic virus vectors (transmitters). Some of them include whiteflies, aphids, nematodes, thrips, etc.

Keep in mind that a mint root can be already diseased before you plant it. Humans can even accidentally transmit them via unclean tools or improper disposal of diseased plants.

How to Get Rid of Them

There is no cure for viral diseases. The best way to get rid of them is to cut off diseased leaves with gardening shears. Please disinfect your tools before and after using them to prevent further spreading of diseases.

Keep an eye on your other plants, if you have them, in your household. Chances are your mint will get infected if other plants are already attacked.

Sometimes, you’ll need to dispose of the entire plant if it’s severely damaged. My suggestion is to wrap the plant in a paper bag and throw it immediately into the garbage bin.

Don’t leave any remains. Also, get rid of the soil and disinfect the pot your diseased mint was growing in.

The best way to make sure that the virus is gone is to burn the infected plant. Still, this is only recommendable if you do it outside in an open space and if you’re sure of what you’re doing.  

Pest Infestation

Pesky pests can cause all sorts of damage to your mint. A portion of them leave white netting or silver stripes, while others are white and inhabit your plant’s surface.

Either way, they leave white dots behind. In my experience, white dotting produced by insects and spiders is much easier to recognize than when it comes to fungal or viral diseases.

A few insects, like a mint flea, produce white larvae that eat the root of your plant. Even though they’re white in appearance, they don’t cause any white-dotting symptoms, so they’ll be left out of this list.

Some of the most common pests are spider mites, whiteflies, and mealybugs.

Spider Mites

These arachnids are related to spiders, ticks, and scorpions. They love sucking the juice out of your mint’s leaf tissue and leave small holes in them.

By sucking the chlorophyll out, spider mites leave tiny white dots that resemble dust behind. This shouldn’t be alarming if you notice a small amount of them.

However, get ready to fight them with tooth and nail if you encounter a larger colony. Oh, and did I mention they leave web too? Because they do!

They leave a net of white trails all over your plant. They also use webbing to create bedding that protects their eggs. Aside from that, a large attack on your plant can be fatal.

How to Get Rid of Them

Pour a strong stream of water on your plant in case of a smaller infestation. Make sure first that your plant can handle it.

Oh, and wash the undersides of the leaves too because that’s where the spider mite party’s at. Prune the damaged leaves with shears and carefully lay them aside, preferably in your garbage bin.

Neem oil is an alternative solution, but make sure to dilute it in the water! Pure oil can damage your mint. Spray the entire plant with it early in the morning, about twice a week, for 3-4 weeks.

Ladybugs are a way to go if you want some additional friends. Mites are their favorite food and they’ll devour them in no time.

Whiteflies and Mealybugs

These sibling insects have a lot of things in common, so I’ve decided to put them together. They both cause white masses on the surface of your plant above the ground.

Like spider mites, they suck out bodily juices, which renders the plant too weak to undergo photosynthesis. The results are pale spots and dots on your once healthy plant.

Mealybugs leave a fluffy white mass that contains eggs underneath the leaves. Whiteflies do this too! You might not notice them at first, but they reproduce at an alarming rate. Before you know it, they will suck the life out of your mint and move to another green plant.

How to Get Rid of Them

The good thing about sibling pests is that you can use the same methods to get rid of them. You can wash them away with water. However, these insects prefer young plants, so they might not be strong enough to endure a water stream.

In that case, spray them with insecticidal soap. I recommend using it in the evening, when the temperature falls, to avoid stressing the plant out if it’s a hot day. Also, there’s less chance to spray any beneficial bugs.

To completely get rid of them, you’ll have to destroy adults, larvae, and eggs. Make sure to clean your plant with water after the treatment is done.

Oh yes, ladybugs too can fight them off. Remember when I told you to use ladybugs on spider mites? Well, maybe now you have some extra ladybugs to fight off whiteflies and mealybugs too! You can always send them back into nature when they’re done feasting.

Improper Nutrition

White spots on a mint can occur more often when it comes to nutrition deficit and inappropriate fertilization. Some elements and compounds are key to retain that luscious green color and lack of them causes the plant to turn white, dry out, and die.

Iron Chlorosis and Manganese Deficit

Iron is the boss when it comes to enzyme and chlorophyll production. Many processes in your mint depend on it. Lack of chlorophyll equals a lack of green color, which leads to chlorosis.

You can spot it easily if the main vein is green but the leaves turn pale-white. Correspondingly, manganese deficit comes hand in hand with lack of iron. This microelement is important in the process of photosynthesis.

The symptoms are more-or-less similar to the iron chlorosis, except the lack of manganese can be spotted more on the newer, upper leaves, due to its immobility through the plant.

Solution

Soil mismanagement leads to an iron deficit. Manganese deficit is mostly connected to iron problems. Try to improve the draining of the soil so the roots can absorb these metals easily.

Phosphorus-rich fertilizers tend to disrupt iron transmission too. When choosing a new fertilizer, make sure that P, the middle number in NPK (nitrogen, phosphorus, potassium) is low.

Magnesium deficit

Magnesium is needed to capture energy from the sunlight during photosynthesis. Therefore, the lack of this element causes the plant to wilt, and older leaves become white-dotted.

Solution

Parallel to iron and phosphorus, magnesium and potassium are antagonists. Try to fix your soil by feeding it with a fertilizer that’s lower in potassium (K). Sometimes fertilizers have the formulation N-P-K (Mg), so try using one of those or use ones rich in magnesium nitrate.

Hard Water and Overwatering

I’ve already explained overwatering because it passively causes white dots on the plants mostly due to nutrient deficiency. On the other hand, hard water is related to the low quality of your water.

Your mint intakes good and bad minerals through the water. Accumulation of white limescale is a result of using hard water. The term hard water means that the water is heavy in calcium, which deposits on top of the leaves surface after the water evaporates.

Solution

You can clean your plant with a vinegar solution. Mix 1 tablespoon of vinegar with 1 quart of rainwater and wash your plant gently with a sponge or a cloth.

Long term solution is to check your water quality and use rainwater or melted snow (if possible) whenever you can.

Dust on Leaves

Sometimes, plain dust can cause white dots on your mint. Not cleaning regularly, leaving home for some time, or placing your mint on a far-reaching spot can cause dust to accumulate. And after reading this article, you might think powdery mildew or spider mites went for your dear mint.

But in the end, it’s just some dust. Nevertheless, make sure to get rid of it. Dust can prevent the plant from getting enough sunlight, which leads to weakened growth.

Solution

Plants deserve a warm, bubbly bath every once in a while, too! Wipe its leaves clean with a damp cloth or spray it with a bit of lukewarm water. A dust brush can do the trick too if you promise to be gentle with it!

Can I Eat Mint Leaves with White Dots?

In most cases, the answer is yes. You can eat your mint, put it in a cocktail or additionally flavor a cup of tea with it. Before digesting it, check if the white color comes from spider webs, pests, or fungal infections.

In such cases, it’s best to heal your plant first and then eat it. You can eat it if you wash the insects and impurities off of leaves, but I prefer to rejuvenate my mint first.

Another tip is to smell your plant. Spoiled mint has a foul smell to it, mostly produces by fungi on it. Also, the taste will be a lot more bitter than usual.

Conclusion

Everyone loves the looks, the smell, and the taste of fresh mint. I mean, how can you not love it? Sometimes, these attributes are violated by exterior and interior factors.

White dots primarily show up on the leaves and sometimes also on the stems. There are many causes for this occurrence.

Fungal and viral diseases disrupt the plant’s digestion, pests suck the water and sap out of the leaves, imbalanced nutrition leads to discoloration whereas dust and limescale accumulate on top of it all.

Luckily, I’ve provided you with solutions to these problems so you can give your mint the treatment it truly deserves!

(Source: Institute of Agricultural Sciences, National Research Council, Spain)

Arifur Rahman

I'm the owner of gardenforindoor.com. After completing my bachelor of science in agriculture, I'm serving as a civil service officer at the Department of Agricultural Extension, Bangladesh. I started Garden For Indoor to make your indoor gardening journey easy and enjoyable.

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