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Leaf Spot [Fungus Symptoms & Treatments]

Do you know fungal leaf spot is a widespread problem for many plants, leading to significant economic and ornamental losses for the growers?

Leaf spot is caused by harmful fungi that invite irregular-shaped spots, yellowing, browning, and leaf lesions, which are effectively treated by pruning and sanitation, cultural or biological control, and fungicides.

Find out how susceptible your plants are to fungal leaf spots and ways to identify and mitigate them.

Fungal Leaf Spot Symptoms

Fungal leaf spot is a type of plant disease that is caused by various kinds of naturally-deriving fungi that are typically favored by warm, moist conditions.

Each fungal infection may invite various problematic appearances, such as circular or irregular-shaped spots, leaf discoloration, and a dark or necrotic center surrounded by a yellow halo.

The naturally-deriving fungi, including Alternia, Cerspora, Septoria, Phyllosticta, Fusarium, Colletotrichum, etc., will infect a severely weak plant or those grown in poor conditions.

Fungal Leaf Spot Symptoms
You can identify different fungal leaf spot through this chart.

However, do not confuse it for leaf blight, which is caused by fungal pathogens and exhibits similar signs, and sometimes may even cause plant death.

Although leaf spots can quickly progress and affect many leaves, they may not necessarily cause plant death.

  1. Small, circular spots: It typically causes small, circular spots to form on leaves that are tan, brown, black, or yellow in the shade and may have a dark margin.
  2. Darkened veins: In some cases, the leaf veins may also become discolored, turning brown or black.
  3. Yellowing or browning: The affected leaves may turn yellow or brown and drop. In severe cases, entire leaves or branches may die back.
  4. Premature leaf drop: The severity may cause infected leaves to drop prematurely.
  5. Distorted growth: Fungla spot causes the affected leaves to become distorted or misshapen.
  6. Powdery or fuzzy growth: Some fungal leaf spots invite powdery or downy growth on the leaf surface, often a sign of a fungal pathogen.
  7. Lesions on stems or fruit: Some types of fungal leaf spot causes lesions on stems or fruit, often indicating a more advanced infection.

Bacterial vs. Fungal Leaf Spot

Determining whether your plant is suffering from fungal or bacterial infection is handy to find an appropriate treatment.

Here are some stark differences between bacterial vs. fungal leaf spots and ways to identify them.

Identifying FactorsFungal Leaf SpotBacterial Spot
DefinitionA type of plant disease that is caused by various types of fungi that infect the leaves of plantsA plant disease caused by various types of bacteria that infect the leaves of plants
ExamplesAnthracnose, powdery mildew, septoria leaf spot, didymosporina leaf spot, and cercosporaXanthomonas leaf spot, Pseudomonas syringae leaf spot, Erwinia amylovora, and acidovorax avenae
Shape of the lesionsIt typically produce circular or irregularly-shaped lesions on leavesIt often produce angular or straight-edged lesions
Color of the lesionsFungal leaf spots are typically brown, black, or yellowBacterial leaf spots are often dark brown, black, or dark green
Discoloration of veinsIt does not usually cause discoloration of veinsIt often cause veins to turn yellow or brown
Spread of the diseaseFungal leaf spots tend to spread slowly over timeIt can spread rapidly under moist conditions
Host rangeSome fungal pathogens that cause leaf spots may be specific to certain plant species or generaIt infect a wide range of plant hosts (for example, the Xanthomonas campestris causes leaf spots on many species, including tomatoes, peppers, and cabbage

Although the fungal spot is more common in plants, bacterial leaf spot diseases can cause severe damage to crops.

If your Orchid has developed black spots on leaves, find the causes and solutions immediately.

Fungal Leaf Spot Treatment Measures

Treating fungal leaf spots is essential to prevent the spread of the spot fungal disease and reduce its impact on plant health and yield.

If left untreated, it can cause significant damage to leaves and plant yields.

In severe cases, defoliation and leaves falling off may weaken the plant, making them more susceptible to other diseases and pests.

Here are some proven measures to treat fungal leaf spots.

1. Apply Fungicides

Fungicides effectively inhibit the growth of fungal pathogens and help prevent further spread.

You can apply fungicides in two different ways.

  • Contact fungicides – Fungicides remain on the plant’s surface and are more appropriate for immediate treatment.
  • Systemic fungicides -Fungicides get absorbed into the plant tissue and provide longer-lasting protection appropriate for treatment and prevention.

Always use copper-based fungicides, including chlorothalonil and azoxystrobin.

  • Timing of application: Time it to coincide with the early stages of the disease. A fungicide application may be less effective if the condition is already well established.
  • Application frequency: Remember to apply them according to the label instructions and in the appropriate dose for the specific crop and pathogen to prevent reduced efficacy.

2. Cultural controls

Cultural control is a treatment and preventive practice to reduce the incidence and severity of fungal leaf spots.

It helps creates conditions less favorable for fungal growth and development, for example:

  • Pruning: Pruning infected leaves and branches helps prevent the spread of the disease, especially in spring and summer.
  • Sanitation: Regularly trim and destroy infected plant debris to reduce the inoculum in the field.
  • Irrigation management: Avoid overhead irrigation or wetting the foliage. Use drip irrigation to reduce the amount of moisture on the leaves instead.
  • Crop rotation: Rotating crops help reduce the build-up of fungal pathogens in the soil. Check out this video to learn more.

3. Biological controls

Biological controls involve using beneficial microorganisms or natural enemies to control fungal pathogens.

Here are a few examples:

  • Biofungicides: Microorganisms compete with the pathogen for nutrients or produce toxic substances that inhibit pathogen growth, such as Bacillus subtilis and Trichoderma spp.)
  • Antagonistic microorganisms: They actively suppress the growth of fungal pathogens by inhibiting fungal growth, such as Pseudomonas fluorescens and Streptomyces spp.
  • Plant extracts: Apply antifungal elements like neem, garlic, and onion extracts on infected leaves.
  • Beneficial insects: Introduce predatory mites and beetles that control powdery mildew and other fungal diseases.
  • Soil amendments: Improving the soil with compost and biochar helps promote the growth of beneficial microorganisms to suppress the growth of fungal pathogens in the ground.
Here are some ways to identify and treat pest infestation on leaves.

Fungal Leaf Spot Preventive Measures

Here are some proven measures to prevent the onset of fungal leaf spots.

  1. Cleanliness and Sanitation: Trim tall grasses and clear leaf debris in fall and winter to prevent the pathogen from collecting in the ground.
  2. Avoid overhead irrigation: Avoid overhead irrigation to prevent foliage from staying wet for an extended period. Instead, use drip irrigation by applying water directly to the soil.
  3. Proper plant spacing: Avoid outdoor and indoor overcrowding, which might create conditions conducive to fungal growth.
  4. Disease-free seed: Always buy certified disease-free seeds.
  5. Fertilization and irrigation: Proper fertilization and irrigation help ward off the risk of pests, making them less susceptible to fungal infections.
  6. Scouting: Regular scouting of plants help detect fungal leaf spot early, allowing for prompt treatment and reducing the likelihood of severe infections.
  7. Nutritional management: Appropriate fertilization is the key, as excessive nitrogen can make plants more susceptible to fungal infections.
  8. Resistant varieties: Choose plant or crop varieties resistant to fungal pathogens to reduce the incidence and severity of fungal leaf spots.

One way to prevent fungal infestation on plants is by applying camphor solution.

From Editorial Team


Fungal leaf spots can weaken the plant by reducing its ability to photosynthesize, leading to reduced plant growth, and yield.

Therefore, you should always keep preventive measures in check to ward off the risk of fungal infection.

Practice crop rotation, proper irrigation, regular sanitation, and plant monitoring to catch the early signs of fungal spread.