Mint is one of the most popular herbs in the world. Its distinct taste and medicinal qualities make it revered in health, beauty and catering. It is extremely hardy and from a single seed, you could end up with a vegetable patch full of delicious mint keeping you in a summer-long supply of mojitos!
But this does not make it immune from issues and white spots on mint leaves are one of the more common problems that crop up. Let’s investigate why they occur, what can cause them and how to treat and prevent them.
What Are The White Spots on Mint Leaves
White spots appearing on your mint leaves can indicate several issues and it is important to properly identify the cause to be sure you are treating the right problem effectively. Pest attacks, fungal diseases and viral infections are the three most common concerns.
1. Powdery Mildew Disease
Little white patches that appear on the healthy leaves of the mint plant are almost certainly a sign of powdery mildew. It is a common fungal disease that finds its way into the garden through the soil or on the wind and whilst not a killer, it is not something you want on your plants as it can spread through your garden rapidly. It will put your plants under strain and slow down growth.
2. Spider Mites or Thrips
Although no relation to spiders, these mites have 8 legs hence the name! They have a waxy abdomen that helps them to move around with little resistance. They thrive in warm and humid conditions.
When mint is attacked by spider mites you will notice clustered white discolouration on the leaves. You can double-check it is spider mites by turning over the leaf where you will likely find the mites burrowing.
Thrips also enjoy dining on mint. These can be identified through silvery patches on the leaves. They lay eggs on the leaves and multiply quickly draining the leaves of nutrients. They can also trigger virus growth.
3. Viral Infections
Mint plants are prone to a lot of viral infections. The mosaic virus is one of the most problematic and common. It can be identified through a mosaic-style pattern of white, yellow and green on the leaves.
Other lesser observed virus strains present in the atmosphere that can leave white spots include Tobacco Ringspot Virus, Cucumber Mosaic Virus, and the Tomato Aspermy Virus. Some of these can be transmitted by pests, such as aphids, whiteflies and thrips.
Reasons Mint Plants Get White Spot
Over or Underwatering
Overwatering a mint plant can cause a nutrient deficiency in the soil as it washes the goodness away. This can lead to white spots all over the leaves of the mint. Letting your plant dry out and then adding some feed to the water should remedy this.
Using hard water can also cause white spots to appear which are just limescale deposits. Hard water is heavy in calcium so when the water evaporates deposits of this are left on the surface of the leaves. You should consider using collected rainwater if you know you live in a hard water area.
Although very hardy, mint plants still need a solid watering schedule, especially in the warmer months. If you notice the plant starting to wilt and going crispy around the edges, it is highly likely to need more hydration.
Temperature and Humidity Issues
Mint prefers a mild temperate climate so I find if we have a spell of very humid weather it can cause issues. For example, the fungal spores responsible for powdery mildew and other diseases are formed in the presence of high humidity. Powdery mildew spores thrive when average temperatures rise above 70F.
Lack of Nutrients
There are 3 main nutrient deficiencies that can lead to white spots: iron chlorosis, manganese deficit and a magnesium deficit.
Iron is very important to produce chlorophyll and enzymes. Without chlorophyll, there will be no green colour in the plants, which results in chlorosis. If the main vein of the leaf is green, but the rest of the leaf is white in colour your plant is likely suffering from iron chlorosis.
If the plant is deficient in iron this will also impact its manganese levels. This can lead to further discoloured leaves as manganese is important in the process of photosynthesis.
A simple feed may remedy this in the new growth of the plant. Improving the drainage of your soil will also help.
Magnesium is also key for mint as it captures energy from the sun for the process of photosynthesis. A deficiency will cause the older leaves to be dotted with white spots. Magnesium is often lacking in acidic soils so treating this before planting is key.
Pests, viral infections and fungal problems can all spread between plants in a garden. Proper spacing and the removal or treatment of any contaminated plant in your garden will help stop the spread.
How To Prevent Mint Leaves from Getting White Spots
Prevention is better than cure when it comes to white spots on mint leaves. If you spot a single mint plant that has become infected with a fungus or viral issue it is often best to try and discard that plant to save the rest.
The best way to prevent pests is by spraying your plant with water. Spider mites and thrips are not fond of harsh jets of water so this will wash them away and make them think twice about returning!
A solid feed and watering schedule will also help your plant thrive and prevent any white spots that may be caused by over-watering.
The application of a nutrient-rich fertilizer will help prevent any deficiency-based issues later in the season.
How To Get Rid of White Spots on Mint Leaves
If the white spots are embedded within the leaf from pest infestation, watering or soil issues then the easiest solution is to pick off the spoiled leaves, treat the issue and then allow the plant to recuperate and produce fresh green mint leaves for you.
If the white spots are actually fungus or spores, it is possible to remove them with a small plastic knife or toothbrush. Simply scrape the white mould off the leaves with the tip of the blade or brush being careful not to scrape off any of the green parts of the leaf.
Treatment for White Spots
It depends largely on the cause of the white spots but here are a few of my tried and tested treatments.
Neem oil is my go-to treatment for pests as it is non-toxic. You can apply neem oil directly to the leaves or use a gentle cloth to spread it.
For powdery mildew, my top tip is to make a concoction of 3 parts baking soda and 1 part water, mix it together and spray onto your leaves.
Remove Affected Leaves
Strategic trimming of infected leaves is always wise whatever the cause and the removal (plus treatment for the underlying cause) should help to deter further white patches from appearing. Within 3-4 weeks you should find yourself with a luscious green mint plant free from white spots and ready to use.
If your plant has been overtaken by white patches or you have a severe pest or viral issue it may be wise to just discard that plant to stop further spread around your garden and start again.
Stopping The Spread of White Spots
Proper spacing in your garden or opting to keep your mint in a contained pot away from your vegetable garden (which also stops it from rambling out of control!) will stop the spread of white spots.
If you do have your mint in the garden, discarding any plants badly impacted will halt the spread and good plant hygiene and husbandry will also help.
Can you Eat Mint Leaves With White Spots?
In short, yes, but it is perhaps not advisable. As mint is used in most recipes for its distinct flavour it is always wise to rejuvenate your plant first to maximise this taste from the leaves and ensure the plant is free of pests, mould, fungus or any mineral deficits.
If the leaf is in an otherwise good condition and you are certain you will not be ingesting anything untoward, then it is fine to eat a slightly dis-coloured leaf that otherwise looks edible and has been washed thoroughly.
However, if the plant has a foul smell alongside the white spots then you will find it will also taste bitter. A plant in this condition is best discarded.
Verdict: Mint Leaves With White Spots
There are many causes for white spots appearing on mint, some more sinister than others.
Always err on the side of caution but in most instances if you remove the impacted leaves from the plant, treat the underlying cause and let the plant rejuvenate for 3 to 4 weeks you should soon be enjoying homegrown mint once again.
Powdery mildew is essentially spores sitting on the leaves so it should rub off using a soft toothbrush or a plastic or blunt knife. You should still treat the underlying cause but it is possible to scrape off the spores.