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What Causes Spots on Leaves? [Tips to Manage]

Have you ever found patches or marks on your plant’s leaves? Those visible damages on the leaves are spots, and these infections can be so destructive that your plant may even die if severe.

Generally, leaf spots vary based on color and their causes, including pathogens, insects, nutrition, or environmental factors. So, choose healthy seeds, use disease-resistant plants, prune, and apply fungicides if the symptoms prolong.

Leaf spots are relatively easy to notice if you closely observe your infected plants. If you are in a hurry to get rid of plants with leaf spots, this article will change your mind!

What Type of Disease is Leaf Spot? 

Any leaf spot starts from pathogens invading the older leaves, penetrating the leaf tissue, and establishing themselves.

Those pathogens are transferred from different mediums, such as wind, water, soil, or debris.

Eventually, the invasion will result in small spots that grow bigger and gradually spread to whole plants.

The spots on leaves can recur with the shade of black, brown, gray, yellow, red, white, orange, rust, and green. 

bacterial spots on leaf
Ornamental plants are mostly affected by bacterial infections leading to spots.

In the case of trees, most leaf spots affect only a small area of trees and cause minor stress, but if it recurs annually or 2-4 years in a row, it might be a serious issue. 

The most crucial thing is those spots weaken the trees by disturbing their photosynthetic activities.

Additionally, the annual occurrence results in complete leaf loss and may be prone to many pathogenic diseases. 

Comparatively, herbs and houseplants are weaker than trees and shrubs. So, if the spots heavily occur, annual plants and houseplants may result in death.

But, you must be careful with small and newly planted trees as the damage may be destructive.

What Causes Spots on Leaves? [Causes & Solutions]

Leaf spots occur due to many environmental factors, such as low or high humidity, unsuitable temperature, excessive rainfall, and extreme sunlight.

Besides, human care errors, including overwatering or underwatering, are frequent activities from which many plant diseases may arise.

Nevertheless, the major causes of leaf spots are pathogens that develop and invade your plants.

1. Main Pathogens 

Generally, there are three types of pathogens; Fungal, Bacterial, and Viral. If you observe their spots minutely, you can see all of them producing their unique lesions. 

Spots in Leaves due to Fungi

Fungal leaf spots arise mainly on fallen leaves and produce spores in rainy seasons. After that, Wind, water, or insects transfer those spores and discharge them to fresh leaves.

A necrotic lesion with a dark rim and a reddish, brown, or black center develops when the spores germinate in a favorable environment and infect leaves.

Fungal spots on leaves
If the fungal spots arise on the plant’s new leaves, it will lose its growing point.

Usually, fungal spots are irregular and vary from 0.5 to 1.5cm. After that, the size and number of spots gradually increase and spread to whole plants.

If you have a vegetable garden, keep your vegetables such as cabbage, broccoli, turnips, lettuce and sprouts safe, as fungal pathogens are likely to catch these vegetables. 
Treatment Methods
  • Isolate the affected plant as soon as possible.
  • Prune the affected leaves as they cannot be revived.
  • Use the right fungicide for your plants.
  • Spray fungicide with sulfur or copper octanoate, or Neem oil
  • Or apply a mild baking soda solution, using 1/2 teaspoon per gallon of water.

Spots in Leaves due to Virus 

You may encounter chlorosis on the leaves of your plants, turning them freckled yellow-green with necrotic rings. If so, it’s due to viral infection, which may cause wilting foliage.

Viral leaf spots occur due to the transmission of viruses into fresh plants from different mediums such as insects, seeds, vegetative propagation, etc.

However, the infected leaves will not exhibit any infections to the naked eye. Since they are microbes, they are visible only under a microscope.

Unfortunately, there is no treatment for viral spots. You can only prevent the plant from viral pathogens if it faces them.
Viral pathogens infect the vegetables such as beans, peppers, tomatoes, etc. 

Spots in Leaves Due To Bacteria

You can easily recognize bacterial leaf spots from their angular, light necrotic lesions, which often darken with age.

These spots may be 5mm to 1cm wide and irregular, often bordered by leaf veins. 

Eventually, those lesions, dry and become delicately thin. The spots may also appear on the dorsal or ventral side of the leaves and kill the tissue section after they cluster. 

You must be careful when the surrounding environment is cool and wet because the spots mostly become apparent under such conditions.

Moreover, bacterial leaf spots on the older leaves are obvious, but eventually, they may appear on the newer ones too.

Bacterial pathogens may infect tomatoes and pepper crops, strawberries, and other annual and perennial plants in the garden.
Treatment Methods
  • Isolate the plant and monitor it daily.
  • Remove all the heavily affected leaves, as they can’t be green again.
  • Apply sulfur sprays or antibiotics with copper on leaves weekly at the first sign of disease.

2. Pest Vectors

If you are into gardening, you may have seen the insects and mites feeding upon the foliage of your plants.

These vectors not only injure the leaves, but they also leave their feces on the leaf’s surface, which leads to infection. These infections may arise from excreta and injuries, leading to spots. 

Spots in leaves vary according to insects. Spider mites leave yellow or brown spots, whereas thrips cause silvery spots.

Similarly, White spots on your houseplants may be due to mealy bugs or other pests.

Insects or mites not only feed upon leaves but also carries different pathogens and discharge them into the surface of leaves.

Treatment Methods
Treatment method for spots
If the heavily infected plants do not recover, destroy them to prevent spreading.

3. Nutrition Deficiencies

Insufficient nutrition is the main hindrance to plant development. If your plant grows slowly, it’s likely to be attacked by many diseases.

Eventually, diseases are the main cause of the spots. Here is a list of some nutrients that can cause spots with treatments upon deficiencies.

NutritionsSymptoms Solutions
PhosphorousBrown spotsUse bone meal or phosphate rock.
PotassiumPurple spots on underside of the leaves.Try sulphate or potash on your plants.
ZincBronzed spots of necrosis.Foliar spray of zinc sulphate will help.
BoronRust spots Dilute borax or boric acid and add to the fertilizer.
Copper Necrotic spotsTry foliar spray containing copper sulphate.
ManganeseDark necrotic spotsUse diluted foliar spray of manganese sulphate.
If the leaf spots are from nutrition deficiencies, they eventually fade under proper fertilization. But you can’t remove the spots caused due to pathogenic diseases.

How to Prevent Plants from Leaf Spots?

You can prevent your plant leaves from spots by monitoring and managing your plants’ surroundings daily. 

Always grow disease-resistant plants to prevent spots in leaves due to pathogens. However, it won’t work for the spots due to other reasons. 

  • Ensure that your plants have the right amount of sunlight, humidity, and moisture. 
  • Avoid overwatering the plant, as wet conditions help disease flourish. Try to keep the foliage dry and dust free. 
  • If possible, try to cleanse the big leaves with soapy water. 
  • Choose the best compost for your plants to provide them with sufficient nutrients.
  • Clean old plant debris from your garden to protect your plants from bacterial infection.
  • Make sure you choose healthy seeds from spot-free plants.
  • Do not overcrowd plants; they lack space for growth as they mature.
  • You must prune indoor and outdoor plants in the spring or summer to remove dead foliage and improve new growth.
  • Whenever symptoms begin visible, apply fungicides and bactericides once every 10–14 days. 

FAQs Regarding Leaf Spots

What kills leaf spot fungus?

To eliminate fungal leaf spots, fungicides such as Iprodione, Mancozeb, Fludioxonil, Azoxystrobin, or Penthiopyrad will be effective.

Can plants recover from leaf spots?

Once the plant is infected with leaf spots, it’s difficult to revive it completely. All you can do is remove the infected part to protect the whole plant.

Make sure to prune the infected leaves from the node and avoid removing the foliage entirely. 

What antibiotic treats bacterial infections in plants?

Streptomycin and Oxytetracycline are the only two antibiotics that can be applied to leaves to prevent bacterial infection. Remember that they can be applied before infection to prevent it.

Wrapping Up

Never experiment with any chemicals or solutions on your plants. You may lose your plants if the liquid can be harmful.

Keep in mind that viral infection can be prevented, but no treatment exists.

If your plant has spots due to viral infection entirely, it’s better to destroy the plant, or else it will spread to other healthy plants.