The Pro Farmer

Combatting Early Blight: Understanding and Treating Alternaria Leaf Spot in Tomatoes

Alternaria alternata

This is a fungus attacking many different crops.

In tomatoes it is called early blight.

Concentric spots of Alternaria on a tomato leaf

Its symptoms are round concentric leaf spots that look like dark, water-soaked lesions on the leaves.

These lesions may expand and become brown or black, with a concentric ring pattern.

In severe cases, the lesions can merge and cause the entire leaf to become yellow, die and fall off.

Concentric spots of Alternaria
Concentric spots of Alternaria
Concentric spot of Alternaria
Multiple concentric spots of Alternaria

These symptoms may also transfer to the stems and to the fruits.

Alternaria on a tomato plant’s stem
Tomato fruit infested with Alternaria

Septoria leaf spot, Bacterial leaf spot and Gray Leaf Spot are also common leaf diseases and their symptoms also look the same.

Alternaria leaf spot can be caused by a variety of factors, including high humidity, warm temperatures, and poor air circulation.

The fungus can spread through water splashes, wind, or insect vectors.

It is recommended to use at least 3 kinds of different pesticides,

and alternate between them every 4 days,

in order to overcome pest’s resistance, and completely exterminate them.

For further information about this, read this post , and this post also.

There are 2 ways to eliminate Alternaria leaf spot: Chemical, and organic.


Best pesticides for Alternaria leaf spot / Early blight,

Polyoxin Al


Copper Hydroxide

It helps prevent the germination of fungal spores.

It is proven and reliable to be powerful while ensuring plants’ safety.

This OMRI-listed product comes in a dry powder formula that is easy and convenient to apply.

Features excellent plant tenacity and delivers maximum bioavailability.

Mineral oil

Covers the egg, larvae, nymph and adult stages, causing suffocation.

It leaves no toxic residue on plants.

Bacillus Subtilis

A biological fungicide containing a strain of the bacterium Bacillus subtilis.

The bacterial spores occupy space on the plant surface, and compete with the pathogens; then active compounds called lipopeptides, produced by the bacterium, disrupt the germination, and growth of invading pathogens.

Due to this action, resistance is not likely to develop.

Neem oil

A naturally occurring pesticide, found in seeds from the neem tree.               

Azadirachtin is the most active component here.                                                         

It reduces insect feeding and acts as a repellent.

It also interferes with insect hormone systems, making it harder for insects to grow and lay eggs.

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