Late Blight Control: How to Identify and Get Rid of Late Blights

Late blight is another fungal disease that is common in tomato and potato. It is a major concern not only for home gardeners, but even for commercial growers. It can be devastating in agricultural lands as it can lead to huge losses. Historical records show that the disease has been around since the 1840s, which was blamed for the shortage of potato in Ireland, resulting in famine and death.

What Is Late Blight?

Late blight is one of the most serious diseases for potatoes and tomatoes. Phytophthora infestans is the oomycete pathogen that is responsible for this condition. These are microscopic asexual spores with lemon shape and an average length of 20 to 40 millimeters. It travels quickly and can travel long distances, making it easy to spread the infestation. It is a disease that commonly happens late in the summer, although there are also few instances wherein they can be apparent even early in the season.

One thing that makes it different from most of the fungal diseases in plants is that the pathogen does not overwinter in the ground or plant debris. The introduction of spores and the spread of the disease happen through direct contact with seeds, transplants, and tubers that are already suffering from an infection. Transfer of the spores will be quicker in windy environments and when the temperature is between 70 to 80 degrees Fahrenheit.

Late blight has a reputation of being a community disease, which is in reference to how it can easily transfer from one host to another. Recognizing how huge and serious the problem is, in the USA, an organization consisting of gardeners, researchers, and growers, have been established. This is the one that is responsible for enhancing communication and teaching everyone on what to do get rid of late blight.

Late Blight

Tomato Plants Infected by Late Blights

Identifying Leaf Blight’s Damage

Host Plants

As it has been earlier mentioned, tomato and potato are the most common hosts for late blight. Aside from the latter, other host plants include pepper and eggplant.


Here are some of the most common symptoms that will be indicative of the presence of late blight in your plants:

  • In the case of potato tubers, there will be shallow lesions that are coppery-brown. Even during storage, the lesions can develop, although it will be slow. In the leaves of potatoes, on the other hand, there will be dark and greasy spots. At one point, the lesions will meet. The plant will wilt, and eventually, it will die.
  • Meanwhile, in the case of tomato, oily and large lesions will appear on the upper surface of the leaves. The veins will also become brownish, which will be indicative of pathways of the lesions. The infection will also destroy new shoots, making them turn brown and dry. Fruits will have brown patches and large bumps, which will disrupt its full growth.

Result of Infestation

Late blight can infest host plants in various stages of development, such as vegetative, seedling, and reproductive stages. It affects tubers, stems, fruits, and leaves. They will cause discoloration in the plants and crops may end up being unmarketable. Aside from cosmetic damage in plants, in the case of severe infestation, there will be economic losses. Commercial growers can suffer from loss of profit resulting from minimal crop yield or the inability to sell crops because of the evident damages.

Tomato Late Blight

Late Blight Causes Discoloration in the Plants and Crops

How to Get Rid of Late Blights

Natural and Organic Solutions

To be effective, treatment of leaf blight needs to be done before the disease escalates. With this, most of the controls are preventive in nature. The following are some of the solutions that can prove to be promising:

  • The first thing that you have to do is to choose the right plants, specifically those that are resistant to the disease. In the case of potato, Elba is the variety that is most resistant to the disease. Unfortunately, with tomatoes, there is no variety that can completely resist the pathogens carrying late blight.
  • If you are planting tubers and seeds, see to it that they are free from diseases. Buy them only from reputable nurseries. Careful inspection of the tubers is necessary, making sure that it is free from blemishes and other damages that can be possible indications of late blight.
  • There are also certain practices in planting potatoes that will lessen the likelihood that it will have late blight. Pre-germinating the potato at least two weeks before planting will help. Keeping it in a warm temperature prior to planting will also be vital in making it less susceptible to the disease.
  • Keeping the foliage dry is also a good thing. As much as possible, opt for drip irrigation. This is better compared to watering plants from the top. Also, it is best to water plants in the morning to be sure that it will dry out.
  • Space the plants generously. This will provide them with air circulation, making sure that they will be dry after watering. To add, this will also minimize the likelihood that the pathogens will easily spread from one plant to another.
  • If plants are already showing obvious signs of potato blight, take them out as soon as possible. Do not throw them in the garden. Throw them away from the plants so that infestation will not spread.
  • It will also be good to remove weeds in the garden. This will help to improve air circulation and will keep the soil bed dry. Get rid of nightshades, among other weeds, as they are also attractive to late blight.

Chemical Solutions

Similar to the treatment of other plant diseases, chemicals are often used for late blight, but as much as possible, stay away from this method. Many chemicals may contain toxic chemicals, which can be harmful to humans, pets, and the environment. When using chemicals, it is important to read and follow the instructions from the manufacturer. Proper timing of application is also necessary to yield a high level of effectiveness.

Fungicides are amongst the most effective in treating this disease. In the case of systemic fungicide, the chemicals move actively throughout the other parts of the plant as it grows. On the other hand, with protectants, they coat only a specific portion of the plant.

For pesticides, some of the most common active ingredients and trade names include azoxystrobin (Quadris), cymoxanil (Curzate), and fenamidone (Reason).

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