Have you ever wondered why there are brown spots on your basil leaves? If so, you’re not alone. While it can be frustrating to see brown spots on your basil plants, there are several ways you can follow to address the problem.
This article will discuss the common causes of these brown spots and how to fix them. Keep reading to learn how to keep your basil plants healthy and thriving.
1. Fungal Leaf Spot
How To Fix:
Apply organic fungicide.
The Colletotrichum fungus causes fungal leaf spots. They leave round brown spots on the basil leaves that cause them to dry out and eventually drop to the ground.
This disease results in holes in basil leaves as if drilled through or shot. If the infection is severe, fungal leaf spots can affect the plant entirely, leading to its imminent death.
Fungal leaf spots thrive in moist, humid environments. They can quickly spread to nearby plants when their spores enter water.
Solution: Apply organic fungicide.
| Difficulty | Average ●●●○○ |
| Speed | Fast-acting |
| Things You Need | Fungicide (neem oil or baking soda) Spray bottle Water Protective gloves and eyewear |
How To Do:
1. Wear protective gear like gloves and eyewear.
2. Prepare the fungicide solution following the product label or recipe.
3. Pour the fungicide solution into a clean spray bottle or container.
4. Sprinkle the solution onto all surfaces of basil plants, including the leaves, undersides, and stems.
5. Allow the solution to dry completely.
6. Repeat the process every 7-10 days until the fungal leaf spot symptoms disappear.
2. Fusarium Wilt
How To Fix:
Remove infected plants and practice crop rotation.
Fusarium wilt is a common yet deadly basil disease caused by the fungus Fusarium oxysporum. This is the most common basil disease, especially for the Genovese sweet basil variety.
Fusarium wilt is a notoriously difficult problem to treat as its infection can last for years once its soil becomes infected.
More so, the surface of infected basil plants can infect nearby plants. That’s why it’s essential to remove infected plants as quickly as possible.
Solution: Remove infected plants and practice crop rotation.
| Difficulty | Average ●●●○○ |
| Speed | Fast-acting |
| Things You Need | Shovel Garbage bags Disinfectant (bleach solution or rubbing alcohol) |
How To Do:
1. Wear gloves and protective eyewear.
2. Dig up the infected basil plant, including its roots.
3. Put the infected plant in a garbage bag and seal it tightly.
4. Dispose of the infected plant in the trash or burn it in a designated area.
5. Disinfect all gardening tools and equipment that came into contact with the infected plant.
6. Follow the preventive measures listed above to protect your remaining basil plants.
7. Plant basil elsewhere than where it has grown, as fusarium wilt spores can survive in the soil for up to 10 years.
3. Downy Mildew
How To Fix:
Apply organic fungicide.
The yellowing or browning of the basil leaves with a fuzzy, powder-like grey substance on the leaf undersides are telltale signs of downy mildew.
Infected seeds cause this problem, affecting the plant entirely if left unchecked. The key symptom of this disease is yellowing and browning, which begins from the middle vein of the plant and spreads outward to cover the entirety of the leaf.
Spores can spread quickly through the wind, so the abrupt removal of these infected leaves or plants immediately. If the humidity stays high, the disease will continue to spread, and these lesions will turn brown.
Solution: Apply organic fungicide.
| Difficulty | Average ●●●○○ |
| Speed | Fast-acting |
| Things You Need | Fungicide (copper fungicide or neem oil) Spray bottle Water Protective gloves and eyewear |
How To Do:
1. Wear protective gloves and eyewear.
2. Prepare the fungicide solution following the product label or recipe.
3. Pour the fungicide solution into a clean spray bottle or container.
4. Sprinkle the solution onto all surfaces of basil plants, including the leaves, undersides, and stems. Make sure the solution dries entirely before handling the plant.
5. Repeat the application process every 7-10 days until the downy mildew symptoms disappear.
4. Botrytis
How To Fix:
Apply baking soda or neem oil solution.
Botrytis, commonly identified as gray mold, is another fungal disease that attacks basil in hot and humid climates. You can locate this pathogen by looking for fuzzy gray-to-brown fungal growth on the leaves and stems of basil plants.
Botrytis is seemingly fluffier than downy mildew, making it more noticeable. Infected leaves will quickly disintegrate and fall off, and if lesions take hold of the stem, it could result in the death of the plant.
Solution: Apply baking soda or neem oil solution.
| Difficulty | Average ●●●○○ |
| Speed | Fast-acting |
| Things You Need | Fungicide (baking soda or neem oil) Spray bottle Water Protective gloves and eyewear |
How To Do:
1. Wear protective gloves and eyewear.
2. Prepare the fungicide solution following the product label or recipe.
3. Pour the fungicide solution into a clean spray bottle or container.
4. Sprinkle the solution onto all surfaces of basil plants, including the leaves, stems, and flowers.
5. Make sure the solution dries entirely before handling the plants.
6. Repeat the application process every 7-10 days until the botrytis symptoms disappear.
5. Frost Damage
How To Fix:
Remove affected leaves and provide warmth to the plant.
Cold snaps are among the underlying reasons behind the browning of areas of the basil plant leaves.
Basil plants are easily distressed by cold temperatures because they are warm-weather crops. If exposed to temperatures below 35°F, the leaves at the plant’s surface will generally darken and eventually die.
Frost-damaged leaves can be addressed by buffering against temperature extremes. For convenience, it’s best to grow basil plants during spring and summer unless there’s a greenhouse or low tunnel to protect the basil as it grows.
Solution: Remove affected leaves and provide warmth to the plant.
| Difficulty | Average ●●●○○ |
| Speed | Fast-acting |
| Things You Need | Frost blanket, cloche, or row cover Water Fertilizer Bucket or watering can |
How To Do:
1. Separate the leaves that are black, brown, or yellow. This will help to prevent the spread of disease and facilitate new growth.
2. Place the basil plants in a warm, sunny spot to help them recover from the cold.
3. Water your basil plants regularly and fertilize them every few weeks.
4. Be patient, and make sure to take care of your plants. It may take several weeks for your basil plants to recover from frost damage fully.
6. Nutrient Deficiency
How To Fix:
Amend the soil.
The most common nutrient deficiencies in basil are potassium and magnesium. The lack of these nutrients causes chlorotic regions and brown areas on the leaves between their veins.
Potassium deficiency in basil results in impaired plant growth, yellow and brown leaves that generally start from the edges, poor flower development, and low fruit yield.
On the other hand, magnesium deficiency can lead to the yellowing of the area between the veins of the leaves, its veins turning purple or red, and the basil leaves distorting or curling up.
Solution: Amend the soil.
| Difficulty | Average ●●●○○ |
| Speed | Fast-acting |
| Things You Need | Potassium or magnesium-rich fertilizer Epsom salt |
Providing a fertilizer rich in potassium or magnesium to your basil plants is much needed to address potassium deficiency. A foliar spray made from Epsom salts can also be used, as these salts are a good source of potassium.
7. Sunburn
How To Fix:
Provide shade to the basil plant.
While basil plants are warm-weather crops, they can still get sunburn. This often happens when water on the basil leaves, attracting heat like a magnifying glass.
Sunburn appears when you see dull or seemingly brown dead spots on the surface of the leaves. This is precisely why you must water basil only from the base and do away with overhead watering.
Solution: Provide shade to the basil plant.
| Difficulty | Average ●●●○○ |
| Speed | Fast-acting |
| Things You Need | Watering can Pruning shears |
How To Do:
1. Relocate your basil plants to a partially shaded place to protect them from further sun exposure and direct light.
2. Water your basil plants regularly to help them recover their lost moisture.
3. Prune off leaves that are critically damaged by sunburn. This will help to prevent the spread of disease and facilitate healthy growth.
4. Be patient, and make sure to take care of your plants. It may take several weeks for your basil plants to recover.
8. Cercospora Leaf Spot
How To Fix:
Apply copper fungicide.
Another fungal infection related to overhead watering is the Cercospora Leaf Spot. This stressor leaves water droplets on the basil leaves, producing too much moisture.
Fungal infections are likely to happen as a result of these moist leaves. With that, you must water the basil near the base of its stem and keep the leaves always dry.
This disease can spread through water, wind, and contaminated soil. To prevent this, you must observe proper watering habits, provide enough space for your plants, monitor their growth and quickly remove the infected.
Solution: Apply copper fungicide.
| Difficulty | Average ●●●○○ |
| Speed | Fast-acting |
| Things You Need | Copper-based fungicide Spray bottle Water Protective gloves and eyewear |
How To Do:
1. Wear protective gear and prepare the fungicide solution following the product label.
2. Pour the solution into a spray bottle.
3. Sprinkle the solution onto all surfaces of basil plants, including the leaves, undersides, and stems.
4. Make sure the solution dries entirely before handling the plants.
5. Repeat the process every 7 to 10 days until the Cercospora leaf spot symptoms disappear.
9. Bacterial Leaf Spot
How To Fix:
Remove the infected plant and practice crop rotation.
The appearance of brown or black spots on your leaves that dry out and become holes indicates that your plant has bacterial leaf spots caused by Pseudomonas cichorii. This pathogen can also be seen on the stems if it has brownish streaks.
An overabundance of nitrogen in the soil is one condition for Bacterial Leaf Spot to appear and infect your basil.
The Pseudomonas cichorii bacteria often exist from seeds or transplants that are contaminated. These bacterial leaf spots typically appear irregular or angular and are separated by small veins.
Solution: Remove the infected plant and practice crop rotation.
| Difficulty | Average ●●●○○ |
| Speed | Fast-acting |
| Things You Need | Shovel Garbage bags Disinfectant (bleach solution or rubbing alcohol) |
How To Do:
1. Wear gloves and protective eyewear.
2. Dig up the infected basil plant, including its roots.
3. Put the infected plant in a garbage bag and seal it tightly.
4. Dispose of the infected plant in the trash or burn it in a designated area.
5. Disinfect all gardening tools and equipment that came into contact with the infected plant.
6. Refrain from planting basil in the exact location where it has grown in previous years, as bacterial leaf spots can survive in the soil for up to 4 years.
10. Aphids
How To Fix:
Apply neem oil solution and attract natural predators.
Aphids are tiny sap-sucking pests with white, soft textures and oval-shaped figures. If you notice curled, spotted leaves on your plant or a black, sticky sap on its leaves, that’s a clear sign of aphids damaging your plant.
Aphids are causing problems as they suck the sugars out of the plant and leave a sticky substance afterward. This can cause yellowing of the leaves and the development of brown spots, or the leaves may curl and eventually fall off.
Solution: Apply neem oil solution and attract natural predators.
| Difficulty | Average ●●●○○ |
| Speed | Fast-acting |
| Things You Need | Mild dish soap Water Spray bottle Neem oil Ladybugs |
How To Do:
1. If the aphids are relatively few, you can remove them by hand. You can mash them with your fingers or knock them off the plant with a strong stream of water.
2. Make a soap and water spray by mixing one tablespoon of mild dish soap with 1 gallon of water.
3. Pour the soap and water solution into a clean spray bottle or container.
4. Spray the solution onto all surfaces of the basil plants, including the leaves, undersides, and stems. Allow the solution to dry completely.
5. Repeat the process every 7 to 10 days until the aphids are gone.
6. If the aphids are many, neem oil can be used to control them.
7. Mix one tablespoon of neem oil with one gallon of water.
8. Spray the solution onto all surfaces of the basil plants, including the leaves, their undersides, and stems. Let the neem oil solution dry completely.
9. Repeat the process every 7 to 10 days until the aphids are gone.
10 . You can also place ladybugs in your garden to control the aphids.
11. Slugs
How To Fix:
Apply diatomaceous earth around the base of the plant.
Appearing frequently in moist conditions, slugs are another pest that damages your basil plant. They leave gross slime trails and noticeable average-sized holes that could turn brown or result in dull spots on the plant’s surface.
Aside from appearing in moist conditions, slugs are most active at nighttime. They can easily damage a basil plant if left unchecked.
Solution: Apply diatomaceous earth around the base of the plant.
| Difficulty | Average ●●●○○ |
| Speed | Fast-acting |
| Things You Need | diatomaceous earth Dusting wand or shaker Gloves |
How To Do:
1. Take off any debris surrounding the basil plants, as these may serve as hiding shelters for slugs.
2. In the evening, when slugs are most active, generously apply diatomaceous earth over the soil around the basil plants, ensuring it covers the base of the stems and the undersides of the leaves.
3. Use a dusting wand or any material that can be used to distribute diatomaceous earth over the soil evenly.
4. Diatomaceous earth loses its effectiveness when wet, so it’s crucial to reapply it afterward should there be rainfall or thorough watering.
5. Reapply it every few weeks to maintain its efficacy.
6. To prevent slugs from damaging your basil plants, build a blockade by creating a continuous line of diatomaceous earth around the perimeter of the plants.
7. Inspect and observe your basil plants consistently for signs of slug activity.
8. Repeat applying diatomaceous earth if you notice slugs returning to your plants.
FAQs on Brown Spots on Basil Leaves
You cannot eat brown basil leaves if the browning is due to a disease or pest infestation. However, the leaves are still edible if the browning is due to other factors, such as sunburn or nutrient deficiency.
Genovese, lemon and Thai basil are some of the best basil varieties resistant to diseases.
A basil is overwatered if it has wilted, yellow leaves that may also be drooping. The stems may also be brown and mushy.
Basil plants should be watered deeply, but only sometimes. You must allow the soil to dry out between waterings, but you may need to water them daily during hot and humid weather.
Addressing leaf spot disease requires time and effort, as it will not go away independently. Treating the affected plants with a fungicide is necessary to control the disease.
If the brown spots are due to an infection, it may take several weeks or months before these spots disappear. However, if the browning results from a nutrient deficiency, the spots may disappear only once the deficiency is addressed in a few weeks.
