Causes and Treatments of Black Spots on Basil Leaves

Causes and Treatments of Black Spots on Basil Leaves

Fungal or bacterial infections may cause brown or black spots on basil leaves. Plants’ constant exposure to frost or nutrient deficiency also develop these spots. If you have just observed such spots on summertime basil, figure out the cause for proper treatment. The article suggests ways to circumvent basil leaves-related diseases.

There could be a number of interpretations when black spots on basil leaves begin to appear. We have collected possible research-based reasons for the bug:

Nutrient Deficiency

Basil leaves become yellow or curled if they have nutrient deficiency. Later on, the yellow leaves turn black. It may be the least possible cause yet can’t be ruled out while counting the culprits.

How to Improve Nutrient Deficiency

The addition of balanced and organic compost infuses a soul in basil herb. Keep soil well-drained and moist to flourish plants. Moreover, kelp seven to ten days a month ensures a balance of potassium, phosphorus, and nitrogen. Make sure that soil contains pH levels 6.0 and 7.0 before plantation.


Spider mites, thrips, whiteflies, and aphids are pests that get nourishment from basil leaves. Treatment of their infestation is imperative. Otherwise, black spots take place overall leaves and punctured leaves will begin to fall off. Pests always target leaves having vulnerable and weakened positions. Leaves contain numerous tiny black dots if these are affected by pests.

How to Observe Thrips on Basil

Hold affected leaves in hand and shake them. If there is thrips infestation, micro specks will fall down. Thrips have long and oval shapes. Take into account the soft tissues of Basil as thrips lay eggs here.

How to Observe Aphids on Basil

Aphids leave honeydew that attracts ants. The presence of ants on basil leaves is an obvious symptom of Aphids.

What are Spider Mites?

Spider mites are 1 mm long, in fact, the smallest of pests that affect basil herb. They are unable to fly.

How to Recognize Whiteflies?

Hold a basil plant in hand, shake it, and notice flying insects. Moreover, these pests lay eggs underside of the herb.

Solutions to Getting Rid of Pests

Solutions to Getting Rid of Pests

Remove Infected Parts of the Herb

Follow the suggested solutions for removing black spots on basil leaves.

Removing the infected parts is necessary to nip the evil in the bud. Secondly, harmful pathogens require to be prevented by sterilized shears.

Remove Eggs

Removing eggs from basil leaves is a practical solution. Use soapy water for three to four days. Insecticides can also be used to wipe undesired eggs.

Neem Oil

The application of Neem oil can be very effective to purify basil herb from pests.

Sticky Traps

Sticky traps are very helpful to catch these damaging pests.

Row Covers

Get row covers that are designed to protect plants from pests’ invasion. These covers are breathable so the herb may fulfill its requirement of inhaling and exhaling carbon dioxide/oxygen.

Fungal and Bacterial Infections

Splashing water on basil leaves, as well as insects, can transmit specific disease pathogens that result in brown or black patches. Similarly, Cercospora, Septoria, Colletotrichum leaf spot are fungal infections. The Basil plant is also infected by these infections and causes a brown or black spot on leaves.

Moreover, a bacterial disease like Pseudomonas Cichorii can affect stem and leaves by developing brown patches. The infection also looks like mold.

Treatment of Fungal and Bacterial Infections

A number of fungicides are available on the market. Use a recommended fungicide having potassium bicarbonate. You can also trim the affected parts of an herb. If some sections are highly infected, destroying and removing them is good for the overall health of a basil herb. Plants should receive sunlight regularly.

The usage of natural fertilizers can be an effective treatment of bacterial infections. Changing soil to alter the environment is a very beneficial tactic. Eliminate and terminate affected leaves when the plant is completely arid. Remember, don’t use the seeds of infected plants for the next crop.

Exposure to Frost

Basil herb is found in subtropical, tropical, and hot climates so it cannot bear coldness or frost. Keeping the growing basil plant container overnight in an open atmosphere will be a shock for the herb. Resultantly, its leaves either blacken or die respectively.


The plant may survive and regrow if a few leaves have been damaged. However, trimming the damaged leaves can save the rest of the plants from further damage. Next thing, ensure a moderate temperature for the plant to thrive. Besides it, use hoops or jars to cover the basil plant. This method will protect an herb from frost damage. Moving the plant to a covered location is also a practical step to keep the basil plant warm.


A great number of people don’t know the adequate amount of water that basil plants require. Black spots on basil leaves are the result of overwatering.  


Take basil plant from one place and adjust it into another pot. The pot should have drained and breathable soil for plants.

Recommendations to Keep Plants Healthy

Proper air circulation among plants is necessary for their healthy development. Humid environments do the damage so keep plants out of it. Fungal diseases may flourish due to humidity. If there isn’t sufficient space in plants, lower leave may not get dry out. The phenomenon could be ideal for fungal and bacterial diseases to grow.

Don’t water the basil plant at noon or evening. Morning is an ideal time for this purpose. Always throw water at the basil herb base. Furthermore, soil used for planting should have a healthy volume of phosphorus, potassium and nitrogen. There shouldn’t be a blockage in its drainage. Choose a moveable container or pot which can be moved from one place to another to keep the plant at a balanced temperature.

Observe plants a couple of times within seven days to detect any disease at an early stage. Timely preventive measures can save a plant from black spots on basil leaves and bigger damage.