5 Reasons Behind Brown Spots on Tomatoes’ Leaves

Many gardeners mistake brown spots on Tomatoes for leaves turning brown, but leaf spots are the early stages of pathogenic invasion.

The initial appearance of these spots may be the size of a dot, exactly like a pimple.

Later, they increase their size, spread, and destroy the whole plant in favorable conditions.

So, go through this article to find the causes and solutions before the brown spots on your Tomatoes spread to the entire vegetable garden.

What Causes Brown Spots On Tomato Leaves [Causes & Fixes]

Most of the pathogens, either fungal or bacterial, stay on the soil, being dormant in winter.

Later in the growing season, they produce spores and increase their number in the lower leaves. Diagnose the following causes to fix brown spots. 

1. Fungal Diseases

Tomato plants infected with Septoria leaf spots develop brown spots with dark margins on their lower leaves close to the ground.

Other possible fungal diseases may be Early Blight with irregular brown spots, and Buckeye rots with brown water-soaked marks caused by Alternaria solani.

Treatments and Preventive Measures

• Isolate the infected plant to prevent the spread and immediately trim off the infected parts.
• If the disease is severe, discard the whole plant.
• Remove the old debris and apply mulch with plastics, fabrics, or dried leaves.
• Use copper-based fungicides, but never apply them when the leaves are wet. 
• Mixing 1 tablespoon of baking soda in 1/4 liter of water, you can also use homemade fungicide.

2. Bacterial Leaf Spot

Bacterial Leaf Spot is a rapidly spreading disease that can infect your whole vegetable garden in a short time. 

Bacterial leaf spots transfer from one plant to another by means of air, wind, insects, or infected seeds during planting.

Moreover, overhead watering, infected gardening tools, and contaminated soil are also the reasons behind bacterial inoculation.

Solutions and Preventive Measures

• Use disinfected soil and healthy seeds or seedlings while planting Tomatoes.
• Remove old debris and weeds to prevent spreading.
• Always follow crop rotation to avoid frequent diseases.
• Use Neem oil & Copper spray to prevent the spread of Bacteria from infected plants.

3. Pests and Insects

Moreover, these pests leave disgusting marks on the plant’s foliage and other parts resulting in entire leaf curls and dropping.

Also, various worms and chewers, like snails, Hornworms, etc., consume whole leaves quickly, resulting in complete plant defoliation.

Solutions and Preventive Measures

• Apply biological control methods to prevent insects and pests naturally.
• Use pesticides or neem oil weekly to control the pests.
• Employ sticky traps and plant covers for extra protection.

4. Fertilizer Damage

Sometimes, you may see brown burn patches on your Tomato foliage after fertilizing them.

This may be because you applied fertilizer on the leaves instead of the plant’s base.

Moreover, improper fertilizing and overfertilization may cause brown spots, resulting in whole-leaf browning.

Root injuries due to excessive fertilizer also cause serious leaf burn starting from brown and crispy leaf edges with burnt brown spots.

Solution and Preventive Measures

• Always follow the experts’ prescription while applying fertilizers.
• Use a balanced liquid fertilizer with an NPK value of 10-10-10 every two weeks.
• Applying fertilizer only after watering the plants will help to prevent fertilizer burns.

5. Other Cultural Factors

Tomatoes thrive best in well-drained, fertile soil with a pH between 5.8-7 at 65-85°F temperature. 

Deprived of suitable growing conditions, the immune of your plants may be unable to defend against pathogens.

Solutions and Preventive Measures

• Provide your Tomatoes with eight hours of sunlight daily. Dappled sunlight will be perfect if the temperature is too high.
• Water your Tomatoes daily during the growing season only when the topsoil is dry.
• Use a moisture meter for proper watering. Ensure 80-90% humidity during the day and 65-75% at night. 
• Prune the infected parts with clean and sterilized pruners.
• Only use rainwater or distilled water, as tap water may contain chemicals like chlorine, fluorine, etc.