Agronomist notebook: Tackling early blight attack in tomato crop

Nairobi’s Moi Avenue Primary School pupils tend their tomatoes, grown using hydroponics technology in 2017.

Photo credit: File | Nation Media Group

What you need to know:

  • Early blight affects the leaves, stems and in severe cases, the fruits. The leaves develop brown lesions with concentric rings that are easily visible with the naked eye while some parts turn yellow.
  • The disease thrives during the heavy rain season as spores are easily washed away by raindrops or carried by wind hence spreading faster.
  • One should select certified seeds as the disease can easily survive on the seeds. By doing this, one minimises chances of disease infestation.
  • Early blight results in lower tomato production and increases the cost of production. It should not be confused with late blight, which affects tomatoes, especially during the late stage of the growing season.


Besides battling pests like Tuta absoluta as outlined last week, farmer Moses’s tomato plants have also been affected by diseases.

Early blight is one of them. It is a fungal disease that affects members of the Solanaceae family such as tomatoes, capsicum and potatoes, especially during the cold or rainy seasons. Both greenhouse and the open-field tomatoes are affected.

Early blight affects the leaves, stems and in severe cases, the fruits. The leaves develop brown lesions with concentric rings that are easily visible with the naked eye while some parts turn yellow. 

It first manifests on the older foliage. The leaves may turn yellow and fall off in severe cases. The stem turns yellow and dry. The fruits can easily be affected at any stage of growth.

The disease thrives during the heavy rain season as spores are easily washed away by raindrops or carried by wind hence spreading faster.

Select certified seeds

It can also be spread by human beings while carrying out management practices.

Moses had informed me how he had incurred losses in the previous crop as a result of early blight infestation, thus we needed to prevent a repeat.

In the current crop, only a few have been affected. We had discussed measures to control the disease as follows:

Land preparation must be properly done to remove all the plant residues that may harbour diseases. 

One should select certified seeds as the disease can easily survive on the seeds. By doing this, one minimises chances of disease infestation.

More severe spread

While pruning, we ensured the affected leaves were removed and disinfected the tools to prevent spreading the disease. 

The lower leaves were also pruned as they could be infected when they come into contact with infected soil.

It is vital to work from the unaffected to the infected parts as this prevents the spread of diseases.

In our case, Moses is using drip irrigation system as this provides water to the root zone, hence preventing splash erosion, which results in a more severe spread of the disease.

It’s also important to plant border crops that act as windbreakers around the farm since the spores are also spread by wind.

Copper-based chemicals

We ensured our field was free of weeds, which could also host  the disease.

Also, planting the tomatoes in raised beds helps in preventing the disease since it improves the drainage and prevents the infection from spreading.

We have been doing regular scouting to monitor the growth of the crops. This has helped us manage the diseases through timely interventions.

We sprayed copper-based chemicals to prevent the occurrence of the disease in our first spray. Currently, we are using chemicals with an active ingredient, Mancozeb metalaxyl, to control the disease.

The different active ingredients are used alternatively to prevent diseases from developing resistance.

I have, therefore, trained Moses on the importance of reading the ingredients’ label before using the chemicals.

Personal protective equipment

While spraying, one should wear personal protective equipment to protect themselves against the chemicals as they are poisonous.

Early blight results in lower tomato production and increases the cost of production. It should not be confused with late blight, which affects tomatoes, especially during the late stage of the growing season.

On Moses's farm, we have so far managed to contain the disease. 

This week, we shall be top-dressing with Ammonium sulphate as per the fertiliser programme.

In our next article, we shall discuss the irrigation regime in tomato production.

gianne254@gmail.com

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