I like to grow basil as part of my fragrant and flavorful herb garden. But I found some white spots on the basil leaves and wanted to know what it is. This post contains my research on this problem and how you can solve it.
There are white spots on basil leaves because of powdery mildew. This is a fungal disease that deposits white spores on the leaves. It does not harm the plant but affects the aesthetics and flavor of basil. You can use milk, insecticidal soap, neem oil, white vinegar to get rid of powdery mildew.
I’ve written a lot more details about each of these issues that can cause white spots on the leaves. You’ll also find some preventive measures and solutions that will help you get your basil plant and leaves healthy again.
1. Basil plant is infected with powdery mildew
Powdery mildew is a common fungal disease that can affect the basil leaves. You will find white powder-like material on the basil leaves which is a sign of powdery mildew.
Your basil plant will suffer from powdery mildew if it faces a humid environment. This usually happens because water is splashing on the foliage as you water the plant. This may also happen because the foliage has grown dense and suffers from poor air circulation.
In small amounts, the powdery mildew is not harmful to the basil leaves. However, it will keep spreading and cover the entire leaf. This will impair the photosynthesis and the plant won’t be able to produce enough food.
This will cause stress to the basil plant that will attract more pests and diseases and even end up killing the plant because of a lack of nutrients.
You can use a baking soda spray, neem oil spray, or milk spray to get rid of the powdery mildew. Test the spray on a few leaves so there is no adverse reaction. Leave it on the leaves for 24 hours to check this.
Prepare your own baking soda solution by mixing 1 tablespoon of baking soda, 1 tablespoon of vegetable oil and 1 teaspoon of dish soap into a gallon of water.
I prefer using diluted neem oil as it’s organic, gentle on the plant, and works on many pests and fungal diseases. I mix 1 teaspoon neem oil and a few drops of dish soap in 1 gallon of water.
Spray the solution on all the basil leaves, making sure to also cover the undersides. I recommend spraying this early in the morning because the scorching sun can burn the leaves.
You can prevent fungal diseases like powdery mildew by keeping moisture away from the foliage. Make sure to only water the soil near the base of the plant. Avoid splashing water on the leaves and stem.
You can use a watering can, soaker hose, or drip-irrigation to water the plant. Avoid using a garden hose or a sprinkler system that sprays water all over the plant.
I suggest harvesting the basil leaves often, so you prevent the foliage from getting too dense to create a humid environment. Use scissors or pruners that are clean and sterilized with rubbing alcohol.
You can consider growing varieties of basil that are resistant to some of the fungal, bacterial, and viral diseases. If you find some of the basil leaves are infected, the best solution is to cut these leaves from the plant and dispose of them.
White spots on basil leaves can be caused by a variety of issues, including fungal or bacterial infections, insect infestations, or mineral deficiencies. One common cause of white spots on basil leaves is powdery mildew, a fungal infection that appears as a white, powdery coating on the leaves. This can be treated with a fungicide or by increasing air circulation around the plants. – Em Jones, Gardener & Tomato lover, Tomato Mentor
2. Basil plant is infested with sap-sucking pests
Basil can develop white spots because of infestations from aphids, thrips, whiteflies, leafhoppers, mealybugs, and spider mites.
The pests, like aphids, thrips, whiteflies will feed on the leaves by sucking sap out of them and causing the white spots. Pests like spider mites will leave white webbing on the leaves as well.
Some of these pests, like aphids and whiteflies, could be white and appear as spots on the leaves, especially the undersides. Pests like mealybugs and whiteflies also deposit their eggs and those may be covered with powdery, white material.
You can get rid of pests such as aphids, thrips, whiteflies, spider mites, and mealybugs using a spray of water to dislodge them. I also use diluted neem oil spray to get rid of them and keep them away. I mix 1 teaspoon neem oil and a few drops of dish soap in 1 gallon of water.
Spray the solution on all the basil leaves, making sure to also cover the undersides. I recommend spraying this early in the morning because the scorching sun can burn the leaves if neem oil is present.
Insecticidal soap is another option that is beneficial to get rid of pests. You can make some of your own by mixing a cup of vegetable oil with a tablespoon of dishwashing soap.
You can mix two teaspoons of this insecticidal soap with 2 cups of water and spray the mixture on the basil leaves to get rid of the pests.
You need to keep using the spray of water, neem oil, or insecticidal soap until the pests are no longer visible on your basil plant.
It’s best to avoid humid conditions on the basil plant that can attract pests. Avoid splashing water on the foliage when watering the plant. Use a watering can to only water the soil at the base of the plant. Harvest the basil leaves so there is good air circulation through the plant.
I recommend checking on your basil plant every morning for signs and symptoms of pests. Take action as soon as you recognize that pests have infested the plant.
If your basil leaves are often affected by pests, I would suggest spraying diluted neem oil every couple of weeks as a preventive measure.
There are two common reasons for why your basil might have white spots developing on its leaves. The first is either an insect infestation (more commonly seen if your basil is outdoors), or a fungal disease is growing. If insects are your issue, it helps to plant other plants and flowers that they typically don’t like, around your basil. Planting chives, garlic and onions can help to keep them at bay, as well as avoiding too much fertilizer as many insects like the nitrogen it gives off. – Steve Eakin, Founder of Love My Bonsai.
3. Basil plant is suffering from nutrient deficiency
If the basil plant does not get the required nutrients from the soil, this may show up in the leaves as white spots because of a lack of chlorophyll development.
Nutrient deficiency can occur because of several reasons. The soil itself may lack nutrients. The roots may have got damaged due to overwatering and fungal issues like root rot. So they cannot absorb the required nutrients from the soil.
If you forget to water the basil plant often, the lack of water will cause nutrient deficiency because the roots can’t absorb and supply nutrients from the soil to the foliage.
You need to find the root cause of the nutrient deficiency before you can deal with it. Check the condition of the soil with a soil test to find if it lacks required nutrients. You can provide organic fertilizer and supplements to the soil to enrich it if that’s the case.
Check the condition of the roots for signs of overwatering and root rot. Healthy roots appear white and dry. If you find the roots are blackened, soggy, and smell, that’s a sign of fungal issues. You need to trim the decaying roots and prevent watering until the plant can recover.
If the soil is parched and hard, it can be a sign of underwatering causing the issue. You can turn the layer of soil using a trowel or garden fork to encourage loose soil. Then give the soil a good watering several times so it gets back the moisture-absorbing capacity.
I suggest adding compost or organic fertilizer every month to the soil, so the basil plant always has a good source of nutrients.
I would recommend using either a slow-release fertilizer or a liquid fertilizer for the basil plant. You can use a balanced fertilizer when growing the plant. But once it’s grown, you can use a nitrogen-rich fertilizer that will encourage the growth of the basil leaves.
The other option is to use a liquid fertilizer that you spray on the soil and the leaves. This is a fast-acting fertilizer that is quickly absorbed into the plant. I would suggest spraying the liquid fertilizer once every couple of weeks.
You can spray the liquid fertilizer every day if you dilute it a lot with water. This would be like diluting 1 tablespoon in a gallon of water. Then you can add it to the watering can when watering the basil plant.
Some other options you can use include compost tea that is a very diluted version of compost that you can spray regularly on your basil leaves to provide them with nutrients.
Spray the liquid fertilizer in the morning. If you use after the sun comes out, the liquid can heat and burn the basil leaves.
I would recommend following the instructions provided by the fertilizer manufacturer to figure out how much fertilizer you need to use and how often you need to use it.
Avoid the problem of overwatering or underwatering the basil plant. You should check the soil before thinking about watering it. Stick your finger 2-4 inches into the soil to check this.
You should water the soil only if the finger comes out dry with no soil sticking to it. Give the soil a good watering when you do water.
A lack of certain minerals such as magnesium, sulfur, or zinc can cause white spots to appear on basil leaves. If the spots appear to be caused by a mineral deficiency, the plant should be fertilized with a balanced fertilizer that contains the necessary nutrients. It’s important to inspect the plant closely and look for other symptoms and environmental factors to determine the cause of the white spots. – John Ehrling, President & co-founder of Gardensavvy.com
4. Basil leaves have salt deposits
I use tap water to water my plants and it works just fine. The problem is if the water contains a lot of minerals and salts, that will deposit into the soil and the basil leaves when water splashing on it.
The salt deposits on the leaves are harmless unless there’s a lot of it causing the leaves problems in photosynthesis. But the buildup in soil will cause dehydration in the plant. It cannot absorb nutrients, causing deficiency and further plant problems.
If you already see salt deposits on the leaves and soil, you can use water to spray it off. You’ll need to use distilled water or rainwater to get rid of the excess minerals and salts from the soil. You need to water the soil several times so the excess minerals and salts will leach out from the soil.
If possible, use rainwater or distilled water for the basil plant. It may be expensive to buy distilled water, so it’s better to get a distiller or make one yourself.
The rainwater is the best water you can use as it’s pure but contains the minerals and nutrients that are beneficial for the plants. If you use distilled water, you need to use a good fertilizer that will provide some nutrients to the basil plant.
You can continue to use tap water if you have no choice. But rinse out the excess minerals and salts from the soil every few months using the rainwater or distilled water.
5. Basil plant faces environmental stress
The basil leaves will turn yellow when there is environmental stress as it leads to a lack of nutrients reaching them.
The plant can suffer from environmental stress because of extreme heat, cold, wind, transplant shock, or heavy pruning.
When the basil plant is stressed, it’s trying to protect itself as much as possible. So the nutrient intake of the plant is reduced.
The basil leaves will curl when the temperature is too hot, too cold, or there is a lot of wind. This happens so it can conserve as much moisture as possible. But because of the curling, the leaves can develop white spots as there is less sunlight on the inside.
If these environmental changes are temporary, the basil leaves will recover and get back to their healthy state. You can help the leaves by placing a windbreaker or a row cover that protects them from the intense heat or strong winds.
If you’re growing the basil plant in a container, you can move the container to a location that is protected from these environmental conditions. You can even move them indoors for a short period.
I suggest growing the basil plant in a location that gets 6-8 hours of direct sunlight, but not more than that.
You can protect the basil plant from strong wind by using a windbreaker or growing the plant near a fence or screen.
You can directly grow the basil plant by starting seeds in the right location. If you’re using a transplant, harden the basil plant before moving them outdoors.
This means you get the plant used to the outdoors by placing it outside for a couple of hours every day. The plant will be ready to move outdoors after a week.
6. Basil plant is of a variegated variety
There are basil variegated varieties that have natural white spots or marks on them. One such variety is the Pesto Perpetuo.
These spots are completely natural, and there is nothing to worry about them. So make sure you know what variety you’re growing, especially when starting seeds.
You don’t want to misdiagnose the variety as having an issue and applying solutions that cause unwanted stress to the plant.