Every single vegetable species is associated with common plant diseases. You know when your plant has a disease when you notice any abnormality in its plant parts. This signs of abnormality vary from the color of leafy parts, stunted growth of stem, discoloration of the stem, rotting of leaves, leaf wilts, root rots and so on. The same can be said about the basil plant varieties.

Basil plant has been a popular herb used for its ornamental, medicinal and culinary purpose comes with quite a handful of diseases. Basil leaves are usually prone to diseases mostly during the wet season which is the period in which they are quite sensitive. Disease type can be fungus or bacterial type depending on the condition in which they are grown, care received, and level of exposure.

However, because few chemicals (fungicides, pesticides) were specifically designed for use on basil. A lot need to be known about the Common Basil Diseases and the ample or native ways in which it can be prevented to ensure their proper quality and marketability.

This article is meant to orientate you on the knowledge of basil diseases and ways to prevent or treat them.

Do follow through;

Here are a few diseases specifically associated with Basil plants

1. Fusarium Wilt

The Fusarium wilt is of the fungus disease type and occurs as a result of a pathogen known as Fusarium oxysporum. Fusarium oxysporum is a common saprophytic pathogen that feeds on dead decaying matter, survives in soil debris and can be spread easily by water splash, air, and soil. Sometimes, the cause is when the plant is seed borne. The disease usually thrives in a warm, humid condition.

Once your Basil plant is infected with Fusarium wilt, you notice signs such as:

  • Presence of dark brown stem.
  • Curling of leaves.
  • Asymmetric growth of Leafy parts.
  • Blackening of leafy parts.

Sometimes the affected plant suffers stunted growth, twisting of stems, occasional leaf drop is among a few of the many symptoms.  It is usually a disaster whenever basil seedlings get infected with this disease as rot of the stem gradually occurs which may cause their death in no more than 5-7 days. There is no apparent cure for Fusarium wilt. Therefore, more attention must be paid to prevention and control rather than cure.

2. Downy Mildew

The basil Downy Mildew is a fungus type disease and is usually caused by a pathogen known as Peronospora belbahrii. It is introduced mainly through disease borne seeds, infected leaf parts, wind-dispersed spores from another infected basil plant. 

Once the disease is infected by the named pathogen, the plant will appear as one suffering from nutritional deficiencies as it starts with yellowing of leaves. In its initial stage, the yellowing of leaf occurs starting at the middle vein before spreading over the leaf. The disease thrives typically in humid conditions. 

On first sight, this disease is not recognized as Downy Mildew, and it usually takes a while before adverse symptoms appear. The adverse signs observed are:

  • Chlorotic Yellowing of leaves on the top surface of the leaf.
  • The occurrence of dark brown patches on the plant
  • Grey growths on the bottom surface of the leaves

3. Bacterial Leaf Spot

The bacterial leaf spot in basil can also be termed as Basil shoot Blight. It is a disease of the Bacterial type and it is typically infected by a pathogen known as Psedomonas cichorii. Bacterial leaf spot usually affects plants of the ornamental type and basil derivatives like the Purple basil, African Blue Basil, Christmas basil, Holy Basil. This type of disease also thrives well in moistened soil. Therefore they are more easily spread through the infected soil by means such as water splashing to plant parts. 

Also, overhead watering of the basil plant causes the spread of this disease. Likewise, the high spread of the disease also occurs in a field or gardening location with no regular spacing.

Now, like other common basil diseases, this common basil disease thrives well during warm and humid condition. To know if your basil plant is suffering from this disease type you will observe the following symptoms:

  • Presence of streaks on stem region
  • Presence of scattered water-soaked leaf spots delineated by small veins on leaves.

How To Control Common Basil Diseases

Many a gardener gets disheartened by the occurrence of disease on plants. Mainly, because disease makes the basil plants to be of low quality and renders them unmarketable. Also, there are no specified chemicals actually to curb this disease but only the ones to contain them. However, there is no cause to worry as you can take some active steps to control, prevent, and treat any of the common basil disease types.

Controlling Fusarium Wilt

  • Knowing fully well that Fusarium Wilt is a fungus type disease that thrives in damp, warm condition. Best way to prevent is to deny the disease the form of condition it can easily adapt to.
  • Closely inspect your basil garden. In case you observe any form of the disease infested plant or plant parts pluck/remove from the garden to prevent spread.
  • Give the soil ample time to recover once basil plants have been cultivated.
  • Grow more basil plant derivatives resistant to Fusarium wilt.
  • Ensure you procure viable, non-infested seeds or seedlings for planting on your garden.
  • Avoid overhead wetting basil plants, instead of wet the soil.

Controlling Downy Mildew

  • In wetting the plant, it is advisable to make use of the drip from of irrigation and avoid overhead wetting of the plant leaves.
  • Ensure you practice proper sanitation whenever you are growing Basil plants
  • Management strategies such as the use of Drip irrigation
  • In the field or garden, to practice appropriate sanitation to minimize inoculum levels.
  • Best way to prevent is by growing the basil from the dormant seed stage rather than from seedling.
  • Grow basil in potted soils rather than on direct ground soil.

Controlling Bacterial Leaf Spot

  • Use disease free/viable seed or transplants
  • Ensure there is free air circulation by ensuring a wide field spacing which goes a long way to prevent plant contact with the disease.
  • Do not hesitate to remove diseased leaves from plants and soil surface immediately.
  • Avoid spraying of water to keep the basil leaves dry.

Why Is There Color Variance Of Basil Leaf From Black, Brown, White And Yellow?

1. The Black Color Of Basil Leaves


Usually, the variance in color of basil plants occurs as a result of deficiencies, excessive plant treatments and much more. Here we will examine what causes the black color of basil leaves. Often the apparent sign or symptom of over-fertilizing or infection of leaves is that leaves will appear black under bright light. The main causes of the Black color of Basil leaves are as follows:

♦ Soil Care: Many variables arise whenever the soil where basil plants are cultivated are not well taken care of. An overfertilized soil could give rise to blackening of basil plants. Although, Basil needs a soil rich in nutrients such as Nitrogen. However, because they can still strive in poorly nourished soils, they tend to be highly sensitive to overfertilized ones making them black or discolored. The overfertilized soil also goes a long way to reduce the necessary essential oils in basil plants.

♦ Sudden wilting of leafy parts: A common fungus disease known as fusarium wilt is known through common symptoms such as the blackening and browning of leaves. This disease type infects the basil type by attacking the tissues responsible for the transport of water through basil plant parts.

Spots and Splotches: Many a fungus disease usually causes prevalence of roundish black spots along the leaves of basil. An example is the downy mildew disease in which black spots appear on the undersides of basil leaves.

♦ Insects: We can tag insects as agents of pollination in that they help plants reproduce or label them as vampires since some of their types feed off and damage plants. Insects that suck sap from basil plants cause damage to plant by turning the leafy parts to black.

How to Prevent

♦ Minimize excessive application of artificial Fertilizers.

♦ Fertilize soil using the natural Organic matter.

♦ Avoid overhead watering of basil plants and water at the base of the plant using the Drip irrigation type.

♦ Ensure proper hygiene or sanitation in the garden.

♦ Ensure proper drainage of the soil.

How to Handle

♦ Remove leaves that are either spotted black or colored black.

2. The Brown Color Of Basil Leaves


♦ Pests and Diseases: Most pests usually insects suck up the sap of plants thereby causing the browning and curling of green foliage. Such insect types are in the form of mites, aphids, and thrips. Also, whenever basil leaves come in contact with a fungus disease such as Fusarium wilt (Damping-off disease) also cause leaves to change color to brown.

♦ Water and Sunlight: Excessive addition of water and lack of adequate sunlight to aid proper growth of basil plants may result in symptoms such as the browning of leaves. A normal basil plant requires no less than 7 hours of sunlight daily. Anything less than that could lead to damages to basil plant.

♦ Soil and fertilizer: As much as Fertilizer is quite essential for the growth of plants. Basil plants do not require much application of fertilizers. Therefore any form of excessive or improper fertilization could cause leaves to turn brown. Also, the soil type that favors the growth of basil plants must be neutral or slightly acidic. A highly acidic soil could cause burns, wilting, leaf curling and most especially browning.

How to Prevent

♦ Minimization in the use of Artificial Fertilizers and the increase in the use of Organic fertilizers.

♦ Ensure Basil receives enough water mainly from the soil.

♦ Ensure the basil plants abides with the recommended spacing.

♦ Spray Horticultural oil or insecticidal soap when weather is cool to eradicate insect pests.

How to Handle

♦ Plucking off of affected plant parts or eliminating highly infected plants from the garden

3. The White Color Of Basil Leaves


The underlying reasons why Leaves of Basil change colors to white occurs as a result of:

♦ Sunburn or Scorching of basil leaves: This happens typically during the summer wherein the annual basil plants experience an excessive exposure to sunlight. The effect on the basil leaves appears as rough white patches on the leafy parts. Most plants likely to fall victim of these are those recently transplanted to a new environment where they are not adapted to.

♦ Powdery Mildew: This form of mildew is quite common, and it occurs for many plant types including the basil plant. The powdery mildew appears as a white coating over the surface of leaves and usually spread fast. Powdery mildew appears in the garden that there isn’t enough spacing, excess Shading and low air circulation.

♦ White Insects: Colonies of white insect present on basil leaves usually creates whitish spots on the leaves. This type of white insects is known as Thrips that often find folding the basil leaves over themselves from predators.

How to Prevent

♦ Basil plants grown together in gardens should be well spaced to ensure proper air circulation.

♦ Protect plants by covering with transparent white covering.

♦ Apply insecticides to the plants to kill off white insects.

How to Handle

♦ Treatment of plants from powdery mildew is done by the use of fungicides such as Neem oil. It is done by thoroughly mixing two tablespoons of neem oil with a gallon of water in a hand sprayer. Apply the spray mixture to all sides of the plants including the undersides.

4. Yellow Colour Of Basil Leaves


Yellowing of basil leaves occur as a result of the following;

♦ Improper Irrigation: Yellowing of leafy parts could occur as a result of Root Rot, and root rot is a fungus disease that arises and thrives due to overwatering of soil. The Root Rot at its later stages results to a condition known as Chlorosis which is also known as the Yellowing of leaves. This yellowing of leaves occurs because Root rot has interfered with the ability of the root to absorb water and nutrients from the soil.

♦ Fungal Disease: Much Common basil plant disease usually results in Yellowing of leaves. But one major one is the Downy Mildew is a fast-growing Fungus that associates with yellowing of the basil leaves.

♦ Pests: Many pests when attracted to basil plants feed excessively on the green foliage. An example of such pest is Aphids found at the undersides of leaves and on stem joints. Aphids affect plants by sucking out the plant sap causing Yellowing of leaves.

♦ Nutrients Deficiency: Although Basil plants have been known to survive well even on poorly nourished soils all basil plant varieties generally require more intake of Nitrogen as a nutritional supplement as Nitrogen deficiency can lead to Yellowing of leafy parts.

♦ Growth conditions: Basil plants thrive best at temperatures above 210C during daytime and temperatures above 10oC during the night. Any temperature variations below this could lead to yellowing of leaves. Basil plants also prefer a lot of sunlight for optimum growth. Lack of proper sunlight could also confer yellowing of leaves for basil plants.

How to Prevent

♦ Compliment basil nutritional supplement with the occasional addition of Fertilizers (such as Nitrogen, phosphate fertilizer).

♦ Ensure plant parts receive enough sunlight for there growth.

How to Handle

♦ Pluck off yellow leaves from plants, so it does not affect other plant parts.

Why Is My Basil Wilting And Why Are There Holes In The Leaves?

Causes of Basil Wilting

The causes of basil plant wilting are as follows;

♦ Wilting occurs when the soil is dry

♦ Overhead watering on plant leaves causes basil to wilt on time.

♦ Basil wilting also arises due to fungus diseases such as leaf spots and fusarium wilt.

♦ Wilting of basil leaves also occur whenever the basil plant is allowed to flower, and it is not well pruned.

♦ Cold, freezing conditions also cause basil leaves to wilt.

♦ Basil wilting also occurs due to the common activity of pests such as grasshoppers, slugs, Japanese beetles which causes the weakened leaf to wilt.

How to Prevent

♦ One of the best ways to prevent basil wilting is constantly pruning the flowers.

♦ Since basil plants wilt due to dryness of the soil, measures must be taken to ensure that the soil is moist and well-drained but with a moderate amount of water. The Drip form of irrigation is preferred.

♦ Basil plants should be well spaced to ensure even air circulation.

♦ Planting operations such as Mulching should be done to retain moisture in the soil and prevent the prevalence of wilt.

How to Handle

♦ Once leaf wilt is observed cut or prune off the affected part to prevent spread.

♦ Disease control measures such as the application of fertilizers to contain fungi growth should be practiced.

What Causes The Presence Of Holes On Basil Leaves?

Basil plants are quite versatile as they have a wide range of applications. They are majorly used for the culinary purpose (due to their sweet aroma) and ornamental purpose (well positioned and beautiful flowers). They are quite viable and sun-loving plants. However, the leaves of basil plants develop holes on their leafy part. The presence of holes on basil leaves is usually due to the common activity of pests such as Aphids, Caterpillars Grasshopper, Beetles and slugs. These pests are usually attracted to basil plants due to their sweet, savory scent. These pests have their various means of destroying leaf parts.

Slugs: This forms of pests are attracted to the sweet scent of basil plants. They usually leverage of basil leafy parts, and they carry out their dangerous activity usually during night time. They damage the plant by creating ragged holes on the plant leaves.

Beetles: Typical of this category is the Japanese beetles. They are mostly during summer time. They only feed on tender leaves but spare leaves with the larger vein. They damage basil plant leaves by creating holes resembling a lacy skeleton.

How to Prevent

♦ Cover mulch with diatomaceous earth to prevent the prevalence of slugs or snails.

♦ Grow basil plants in a well-spaced manner.

♦ Spray garden with Pesticides to curb pest occurrence in the garden.

♦ Ensure proper sanitation or hygiene.

How to Handle

Best way to handle the presence of holes is to eradicate these types of pests. This can be done through the following:

♦ Handpicking: pests such as snails and beetles can be handpicked form basil plants.

♦ Cropping practices such as soil rotation should be practiced.

♦ Spraying of insecticidal soaps helps curbs pest such as Aphids that cause yellowing and curling of leaves.

Root Rot In Basil And How To Fix?

Root Rot disease in basil is a disease of fungus type. Root Rot occurs once the root of the annual and perennial basil plant gets infected with fungi. Root rot also occurs when the basil plant is overwatered. 

Root Rot caused by fungus include fungi in the genera Rhizoctonia, Alternaria, and Pythium. This plant condition, if left untreated eventually leads to the death of plants. It can only be detected at an advanced stage because initial infection occurs below the soil. 

For timely detection, you can gently shake the soil from the roots and inspect for rot. Root rot occurs in plant planted in soils that are not well-drained or extremely low porosity. The plant gets contaminated through small roots and spread in a matter 7-10 days. Another major source of infection of Basil plants with Root rot is through infected soil.

Symptoms of Root Rot

As the root is the means where plant derives their nutritional supplements. Root rot interferes with root function and prevents the adsorption of water, nutrients into the plant system. Thereby, generating the symptoms (some of which are of plant nutrient deficiencies. Some of those symptoms are:

♦ Chlorosis (yellowing of Leaves) then browning of leaves of basil plant at it later stage.

♦ At an advanced stage of root rot, the root appears brownish, soft and mushy.

♦ The plant begins to experience leaf drops.

♦ The stem of the basil plant begins to soften, and the entire plant eventually falls.

♦ Wilting of leaves also occurs

♦ Stunted growth.

Ways To Avoid Root Rot

Plant Root rot can stunt plant growth and decrease its viability. Measures must be taken to avoid or prevent it from occurring. The measures are:

♦ Ensure the area of plantation has a proper Temperature. Not too hot or too cold.

♦ Ensure you disinfect all garden tools to prevent contamination

♦ Ensure proper air circulation

♦ Monitor the activities of pests and curb them.

♦ Always prune back the roots of basil plants.

How To Fix Plants Infected With Root Rot

Whatever the source of infection is. Trying out a couple of these how to fix tips helps contain Root Rot.

♦ Start treating Root Rot by washing the roots in running water.

♦ The next thing to do is getting a sharp, clean pair of shears to trim away affected parts of Root

♦ Then dip the remaining Healthy roots in a fungicidal solution.

♦ When replanting in a pot, pour away the infected soil and refill with soil that has good drainage.

♦ Replant into the soil but do not water soil except when dry.


Having a herb garden involve a whole lot of things. More times than often you will be faced with cases of common diseases and insect pests as a gardener who grows plant varieties such as Basil plants. Caring for their varieties requires some mechanical approach. The common plant disease affecting basil plants has been itemized in this article along with preventive approach and solutions on how to fix so that your basil plants do not fall prey to such common plant diseases. We hope this guide helps you to raise healthy basil plants indoors and outdoors!