White Spots on Mint Leaves: 7 Causes & Effective Treatments
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Mint has a reputation for being an extremely hardy plant- and I’ve certainly found that to be true in my own garden. But that doesn’t mean that it’s immune from problems- and mint leaves with white spots are one of the more common issues.
White spots on mint leaves are usually due to one of seven reasons:
- Powdery mildew
- Pest infestations
- Mosaic virus
- Salt built-up
- Nutrient deficiencies
- Leaf sunscald
- Lack of water
In this post, I’ll explain each of these issues, how they can come about and what you can do to help your mint regain its lush green color.
Let’s get started!
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7 Causes for White Spots on Mint Leaves
The reason behind the white spots determines the proper treatment for your plant. I’ll address each cause/treatment in this post, but if you need a quick breakdown, here’s an overview:
Cause | How to Recognize | How to Treat |
Powdery Mildew | Powdery or fuzzy white spots on leaves | Spray with homemade baking soda or milk solution, or use commercial fungicide |
Pest Infestation | Scattered whtie spots, visible pests | Remove severely affected leaves, spray plant with water, use a safe insecticide if needed |
Mosaic Virus | White to light-yellow discoloration between leaf veins | Remove plant and disose of it in the trash. Clean all tools used, and wash hands thoroughly |
Salt Build-Up | Crystalline white deposits on leaf surface | Add a hard-water filter to water source, flush soil with fresh water, avoid over-fertilizing |
Nutrient Deficiencies | Scattered white spots, white leaf edges, stunted growth, yellow/brown leaves | Confirm nutrient deificiency with a soil test; supplement according to the test results |
Leaf Sunscald | Blotchy white spots in leaf areas exposed to sun | Provide shade |
Lack of Water | White leaf tips and edges | Provide water whenever soil feels dry 1 inch deep |
Let’s get down to the details:
1. Powdery Mildew
Powdery mildew is a very common fungal infection to find in your garden. It starts as small white patches that resemble a dusting of white powder or flour- hence the name. Powdery mildew strikes a variety of garden plants, including mint.
I’ve dealt with powdery mildew before, particularly on squash.
Some species of powdery mildew are host specific, meaning that one fungus cannot infect another plant. However, some species can cross over into other hosts. Powdery mildew thrives in warm, moist conditions, and spores typically travel on the breeze.
How to Treat Powdery Mildew on Mint
If any of your mint leaves are severely affected by powdery mildew, cut them off and dispose of them in the trash. Then treat the rest of the plant with simple homemade mixture of either baking soda or milk:
- Baking soda: Mix 1 teaspoon of baking soda, 1 teaspoon vegetable oil and 1/2 teaspoon dishwashing liquid with 4 cups of water
- Milk: Mix milk with water in a 1:10 ratio
I’ve personally used the baking soda recipe with good results.
Whichever treatment you choose, pour your mixture into a spray bottle and spray it on the affected areas several times per week.
Another option is to spray the plant’s soil with a commercial anti-fungal treatment, such as a copper fungicide. Make sure to choose a formula that’s safe for edible plants and follow all the package directions carefully.
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2. Pest Infestations
White spots on leaves are often caused by pest infections, including:
- Aphids
- Whiteflies
- Spider mites
- Thrips
- Mealybugs
These pests feed on plant juices and cause leaf discoloration.
How to Treat Pest Infestations on Mint
Spray your mint plant(s) with the garden hose to knock off as many pests as possible, and prune off any severely damaged leaves. If your plant is indoors and you don’t have a garden hose, use the shower instead.
Keep a close eye on your plant for more signs of pests, and you may need to repeat the spray-down a few more times. If the infestation is in its early stages, this may be enough to successfully treat the problem.
If the bug problems persist, pesticides can be effective- but you need to do it carefully.
I recommend a homemade solution as a first option:
- 1-2 tablespoons of neem oil
- 1 gallon of warm water
- 1-2 tablespoons of dish soap
Spray the mint plant down generously, and check back daily for signs of pests.
If you want to use a commercial pesticide, read the label instructions thoroughly before applying- not every formula is safe for edible plants. Follow the directions exactly, and wear protective clothing and gloves while handling pesticides. And be sure to wash your hands immediately after spraying.
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3. Mosaic Virus
Mosaic virus attacks a wide variety of plants, it’s one of the most common viruses found on mint plants. It gets its name from the white/yellow discoloration between the leaf veins- giving the leaf a mosaic-like appearance.
The virus spreads through contaminated soil, contact with infected plants and some insects.
How to Treat Mosaic Virus on Mint
Unfortunately, there is no treatment for mosaic virus. Once your mint has been infected, you’ll have to pull the plant and dispose of it.
After uprooting the plant, do not put it in the compost or on a waste heap- this could allow the virus to spread to other plants. Instead, place the mint plant in a plastic bag, seal the bag and dispose of it in the garbage.
Make sure to thoroughly clean any tools you use to take the plant out. Also, avoid touching the leaves directly and wash your hands after handling them. Do not replant mint in the same area for at least 2 years to avoid infecting new plants.
4. Salt Built-Up
Excessively high mineral content can show up as white spots on the leaves. Salt is the most common mineral to build up on mint plant’s roots, and it can lead to crusty white spots on the leaves, stunted growth, wilting or even death.
Excessive salt in your mint plants can happen in a couple of different ways.
- Hard water
- Over-fertilizing
How to Treat Salt Buildup on Mint
If your salt build-up problems are from hard water, try adding a filter to your garden hose. For indoor mint plants, I like to use an inexpensive water filtration pitcher to remove excess minerals.
You can also leach the salt away with fresh water. Drench your mint plants a few times to wash away the built-up salt. If your mint is in a pot, make sure the water runs freely from the drainage holes.
Mint typically doesn’t need much, if any, extra fertilizer- it’s an incredible grower all on its own! So if you suspect you’ve been heavy-handed with fertilizing, flush the excess out by drenching the soil several times in a row. Then, go more sparingly on the fertilizer in the future.
5. Nutrient Deficiencies
There are 16 essential nutrients that plants require for heathy growth. A nutrient deficiency means that one or more of these essential nutrients isn’t available for your plant to absorb.
When a mint plant lacks the right nutrients, you can expect to see discoloration on leaves, browning or yellowing on the edges of leaves, inter-veinal chlorosis, younger leaves looking paler than older ones, and spotting.
A deficiency in either potassium or manganese is the most likely culprit behind white spots on mint. A soil test can confirm a deficiency.
How to Treat Mint Nutrient Deficiencies
If you find that your soil is lacking in potassium or manganese, here’s what you can do to fix the situation:
- Potassium – Wood ash, seaweed, kelp, potash, potassium nitrate, or potassium hydroxide
- Manganese – Manganese sulfate/chelate
6. Leaf Sunscald
This happens when your mint plant has been exposed to too much sun. The harsh sun kills off the cells in affected leaf areas, causing the loss of green color.
In prolonged or very severe sun exposure, the leaves become scorched, and they will turn brown and die. But those that have only been mildly scalded will have patchy white or light-yellow spots.
How to Treat Mint Leaf Sunscald
Once the leaf gets scalded, the white markings are permanent. However, it’s pretty simple to prevent further sunscald damage.
Use shade cloth to give your mint some relief during especially harsh weather. This video from The Secret Garden demonstrates how to build a simple structure yourself:
7. Lack of Water
All plants need water, and when there’s not enough moisture to go around, plant cells begin to die. White spots from under-watering often show up first on the outer leaf edges, where the plant tissue is thinnest and most vulnerable.
While mint growing in the ground can get dried out, potted mint plants are at a higher risk for under-watering since they’re in more constricted space.
How to Treat Under-Watered Mint
This one’s pretty simple- make it a point to water your mint plant either more frequently or more deeply.
Mint does best with consistently moist soil, and it’s ready for a drink when the top 1 inch of soil feels dry to the touch. You may need to water your mint plant daily or every few days- it just depends on the environmental factors and how fast your plant is processing moisture.
When to Pull a Mint Plant with White Spots
In instances where the mint plant has been infected by a virus, such as the mosaic virus, or when it is no longer responding to treatment, it’s time to pull it.
If the problem was a plant disease or severe pest infestation, the soil could have been affected as well. So avoid planting mint in that location again for at least one growing season.
Frequently Asked Questions about White Spots on Mint
Final Thoughts
I hope that this article has provided some insight into how to take care of your mint plant when it starts to show white spots and how you can save it so you can keep enjoying your mint.
White spots on mint leaves can be worrying, but in my experience, mint is a hardy plant that can usually bounce back from most of the trouble it may come up against. It’s a survivor, so don’t throw in the towel if you see a few white areas spring up.
I’d love to hear what you think! Whether it’s a question you’re wondering about or a helpful tip you’ve discovered, there’s no better place to learn than from each other. So please feel free to share in the comments!
