How to identify late tomato blight in the farm

Late tomato blight is a fungal disease that affects tomatoes, potatoes, and nightshade. However, the effects are more economically severe on the tomatoes and potatoes. The late tomato blight was responsible for the 1840 Irish potato famine. Spotting the tomato late blight symptoms early is a crucial part of remediation. It also presents itself as spots pun intended.

P. infestans (fungi) can infect and generate thousands of spores, or fungal seeds, in a short time. When the weather favors them, they spread through the air, resulting in widespread transmission of the infection.

Tomato late blight symptoms

tomato late blight symptoms leaves
Tomato late blight symptoms leaves

When you see large, dark brown spots with a green-grey edge appear on the leaves, not contained by significant leaf veins, that is a sign of early tomato blight onset. Once established, the infections will spread through the leaflets and petioles, resulting in vast areas of dried brown foliage in the affected area.

When there is a lot of humidity, thin powdery white fungal growth occurs on the leaves, fruit, and stems of afflicted plants. Thin powdery white fungal growth forms on diseased leaves, fruit, and stems in high humidity.

As you are scouting, look for stem infections too. They are firm and dark brown, with a rounded edge and a rounded edge.

tomato late blight symptoms stem

For the fruits, a cut open green tomato will reveal an infection that is tan to grey. The infection penetrates the flesh of the fruit. The fruit infected with the fungus that causes late blight has dry brown rot.

Firm, dark brown, round patches develop on the surface of the fruit and eventually cover considerable areas of the fruit. The presence of secondary bacteria might cause spots to become mushy.

Also, you may see a considerable portion of the tomato fruit spotted with firm and evenly spaced spots which are round and dark brown. These spots usually have white powdery patches in the central areas.

tomato late blight symptoms fruit

When there is a lot of humidity, powdery white spores grow on the diseased fruit, leaves, and stems of plants.

Cool and wet weather spells doom because it may come with frost. When the frost hits your farm, the whole area under tomatoes turns brown, and the tomato plants also become wilted.

Management of tomato late blight symptoms and disease

Buying tomato blight resistant seeds

The degree of resistance against disease may vary by seed type. So do not be surprised when you encounter tomato late blight symptoms now and then.

Symptoms will appear when conditions are very favorable for infection. The resistance may vary depending on the fungi (Phytophthora infestans gene used.

Grafted tomatoes

Tomato grafting can also be an alternative for increasing resistance to blight, among other diseases. Crop producers have found that grafting desired fruiting varieties onto robust, disease-resistant tomato rootstocks is a cost-effective technique of dealing with a wide range of disease and production-related challenges.

When you graft, tomatoes can increase productivity and overall crop health. They can also minimize or eliminate the need for pesticides in some situations.

Cultural control of late tomato blight

Potato culls might harbor the disease and should not be left on the farm. You should gather all remains into heaps and bury them or add them to the field as manure. You can also feed them to the animals before the next planting season begins.

Contaminated plants can sprout from infected tubers. Therefore, you should reduce volunteer plants or use dried commercial tomato seeds and conserved seeds. These will reduce the risk of infection.

A good practice is checking tomato transplants for late blight symptoms before purchasing and planting them. You identify tomato late blight symptoms early on. For example, tomato transplants transported from southern regions may be infected with late blight.

Finally, take all infected plants away from the farm. Either bury, destroy with herbicide, or flame killed to keep the disease from spreading from one small part to the entire field.

Chemical control of tomato late blight

If you are going to go chemical on tomato late blight, apply fungicides specialized to water molds. You should repeat treatments according to the label directions for them to be effective.

To increase the chances of success, you should apply fungicides before infection occurs. The best time is when the environment is most conducive to the spread of the disease.

Phytophthora infestans are water mold that affects plants.

You should scout the farm regularly for symptoms of late tomato blight. Increase your efforts during weather that is favorable for the establishment of the disease.


Knowing how to identify tomato late blight symptoms will be the deciding factor in how well your crops progress and whether you will be adversely affected by the disease. When you identify the symptoms early, during scouting, you can initiate measures to control or treat them and save your crops before it is too late.


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