Early Blight in Tomato and Potato

Al Ardh Alkhadra > Blog > Agriculture > Early Blight in Tomato and Potato

early blight

Do you know that Early Blight is a common problem in tomato and potato plants?

Early blight occurs due to a fungus: Alternaria Solania.

Moreover, the first symptoms of this disease appear on lower, older leaves as small brown spots with concentric rings that form a bull’s eye pattern.

As the disease matures, it tends to spread outward on the leaf surface causing it to turn yellow, wither, and then die.

Eventually, the stem, fruit, and upper portion of the plant will also become infected.

Furthermore, the disease can severely damage tomato and potato plants.

Early blight overwinters on infected plant tissue and spreads by splashing rain, irrigation, and garden tools.

However, the disease is also carried on tomato seeds and in potato tubers.

Keep on reading to learn more about early blight.

Quick Facts about Early Blight

Early blight is one of the most common diseases in potato and tomato plants, occurring nearly in every season.

It affects leaves fruits and stems and can be severely yield-limiting when susceptible tomato cultivators are used and the weather is favorable.

early blight 1

Moreover, severe defoliation can also take place.

While in tomatoes, this disease can damage the fruits due to the sun.

Identifying Early Blight

In order to identify early blight, keep an eye out for the following:

Initially, small dark spots will form on older foliage near the ground and these leaf spots tend to be:

  • round
  • brown

Moreover, they can grow to about 1/2 inch in diameter.

Larger spots, however, have target-like concentric rings. The tissue around the spots will often turn yellow.

In case there is a severe infection in the plant, the leaves with beginning to turn yellow and fall off, or dead, dried leaves may cling to the stem.

Furthermore, saddling stems are infected or just above the soil line.

The stem turns brown, sunken, and dry, with collar rot.

However, if the infection girdles the stem, the seedling will wilt and die.

Stem infection on older plants tends to be oval to irregular in shape, while dry brown areas with dark brown spots with concentric rings are also present.

It is important to note that this disease can also infect the fruits of the plant at any stage of maturity.

Fruit spots tend to be leathery and black. These are raised and concentric ridges and generally occur near the stem.

Infected fruit may drop from the plant as well.

Learn more about What Do Yellow Leaves Mean: Common Causes here.

Biology of Early Blight

It is important to note that early blight can be due to two related species: Alternaria tomatophila and Alternaria solani.

Both pathogens can infect plants like:

  • tomatoes
  • potatoes
  • peppers
  • several weeds in the Solanaceae family including black nightshade Solanum ptycanthum
  • hairy nightshade, i.e. Solanum physalifolium

Moreover, the disease develops at moderate to warn at about 59 to 80F temperatures, while 82 to 86F is its optimum temperature range.


The pathogen is most likely to spread with any weather or heavy dew or when the relative humidity tends to be about 90% or greater.

Furthermore, the early blight pathogens both overwinter in infected plant debris and soil.

Also, the patholso tends to survive on tomato seeds or may also be introduced on tomato transplants.

Lower leaves can have an infection when they come in contact with infected soil, either through direct contact or when the raindrop splashes onto the leaves of the plant:

  • spores or reproductive structures can germinate at 47° and 90° F and will need free water or relative humidity of 90% or greater.
  • or spores can infect the plants and form leaf spots as small as 1/8 inch in diameter and are as little as five days

However, the spores can also spread throughout the field by wind, human contact, or equipment.

This results in many reinfection opportunities throughout a growing season.

Managing Early Blights in the Home Garden

In order to manage early blight in your home garden consider the following:

Resistant Varieties

Early blight-resistant varieties are readily available in plant nurseries.

As this disease tends to be common in places like Minnesota, grandees should make sure to look into these varieties.

Resistance does not mean that you will not see early blight, rather, it means that they can better tolerate the pathogens.

And so the damage will be less severe than with non-resistant varieties.

You can also refer to Cornell University to keep track of varieties that are disease resistant.

Cultural Controls

Cover the soil under the plant with mulch, like fabric, straw, plastic mulch, or dried leaves.

Moreover, water at the base of each plant with the help of drip irrigation, a soaker hose, or careful hand watering your plant.

You can also increase airflow by staking, or trellising, removing weeds, and spacing your plants at an appropriate distance.

Also, pruning the bottom leaves can help prevent early blight spores from splashing up from the soil onto the leaves.

Let two years pass before you plant tomatoes or peppers in the same location.

early blight 2

Physical Controls

Pinch off th leaves of the plant with leaf spots and bury them in the compost pile.

However, if you touch the infected leaves, wash your hands well before working in a healthy tomato plant.

If you are using pruning tools, make sure to wash and sterilize them after touching infected plants.

It is okay to remove up to one-third of the leaves of the plant if you catch the disease early.

Make sure to not remove more than one-third of the leaves of the plant.

Keep the leaves dry to reduce the spreading of the disease.


Most home gardeners do not need to treat tomatoes with a fungicide.

Tomato plants can tolerate a lot of early blight without reducing the number of tomatoes they produce.

Managing Early Blight On Farms

To manage early blight on farms, follow the steps below:


Early blight often appears in mid to late June. The exact timing, however, varies from year to year.

So make sure to scout regularly in order to start managing the disease as soon as it appears.

Resistant Cultivators

There are a number of resistant tomato cultivators available that are often designated with an “EB” in seed catalogs.

However, you can also find an extensive list of resistant cultivators online on different pathology websites as well.

It is important to note that resistant varieties are not immune to early blight.

But the infection tends to be less severe on either the leaves, stem, or both.

Cultural Control

You can use pathogen-free seeds or collect seeds from disease-free plants.

Moreover, make sure to rotate tomatoes and related crops for at least two years.

Control suspectible weeks like black nightshade and hairy nightsahde and volunteer omato plants throughout the rotation.

control in farms

Make sure to fertilize properly to maintvigorousrous plant growth.

Do not over-fertilize with potassium and maintain adequate levels of both nitrogen and phosphorus in th soil.

However, avoid working in plants when they are wet from rain, irrigation, or dew.

You can use drip irrigation instead of overhead irrigation to keep foliage dry.

Furthermore, stake or trellis and prune the plants to increase airflow around the plant and facilitate drying.

Staking will also reduce contact between the leaves and spore-containated soil.

Carefully prune infected leaves, take care to wash and sanitize tools as you prune the plants and dispose of the infected leaves far away from your tomato production areas.

Apply plastic or organic mulch to provide a barrier between contaminated soil and leaves.

However, during fall, removing or burying infected plants that will help to reduce the likelihood of the pathogen surviving into the following year.

Also, for greenhouse production, early blight tends to reduce by as much as 50% by covering houses with a UV-absorbing vinyl film.


It is important to note that the application of fungicides should be according to the environmental conditions that favor disease to be most effective and according to label instruction.

Once the pathogen appears, make sure to keep track of forecasts and plan applications of fungicides accordingly.

However, it is important to alternate between different chemical families to avoid the development of pathogen insensitivity to a certain active ingredient.

Some insensitivity to chemical family is more common in some cases, so you should be careful to rotate these with other chemical families.

Moreover, if insensitivity is already present, fungicides in chemical family 11 will not provide good control.

Look Alike Diseases

A number of fungal diseases occur on the foliage of tomatoes and can make identification difficult.

Septoria leaf spots tend to produce smaller lesions with tan or light gray centers.

Grey leaf spots also prodcues smaller and lighter brown lesions than what you can see with early blights, and the center of the gray leaf spot lesions will also crack.

Also, most hybrid tomatoes have resistance to grey leaf spots.

However, heirloom varieties lack this resistance.

Late blight will produce lighter tan-colored lesions that have a light green halo.

Moreover, late blight will occur all over your plants including young leaves, whereas early blight is found on the lowe leaves.

Bacterial spots can also be confused ith early blights when the early blight lesions are young and small or when both are present.

In general, a bacterial spot will be smaller, can be water-soaked on the underside of the lead, and the center of the lesions may also fall out.

Leave a Reply

Your email address will not be published.