Alphabetical Plant Listing

Late Blight

How to Identify, Prevent, and Treat Late Blight

What is Late Blight?

Late blight is a serious and highly destructive disease that affects various members of the nightshade family (Solanaceae). It is caused by a fungus-like oomycete pathogen called Phytophthora infestans, which can cause significant damage to the foliage and fruits of the infected plant. The disease can spread rapidly and cause extensive economic losses in agriculture, especially in areas with high humidity and rainfall.

Late blight mainly affects tomatoes, eggplantspepperspotatoes, as well as other nightshade crops.

Late blight is most commonly known as the disease that caused the Irish potato famine in the 19th century, during which millions of people died due to the loss of the potato crop.

What are the Symptoms?

Late blight symptoms can vary, depending on the stage of the disease. Here are some common symptoms of late blight:

  • Water-soaked lesions on leaves that eventually turn brown and dry out
  • A green-gray mold on the underside of leaves
  • Brown or black lesions on stems, often accompanied by a purplish discoloration
  • Brown or black spots on fruit, sometimes with white moldy growth

In humid weather, the disease can spread quickly, causing rapid wilting and death of the plant.

What Causes Late Blight?

The pathogen is particularly prevalent in wet and humid conditions and can spread rapidly in fields and gardens. Late blight can survive on infected plant debris in soil and spread through wind-blown spores, making it a particularly persistent and difficult disease to control.

How to Prevent Late Blight?

Here are some steps to help prevent late blight in your garden or farm:

  1. Choose disease-resistant varieties: When selecting tomato or potato plants to grow, choose varieties that are resistant to late blight.

  2. Proper plant spacing: Proper plant spacing helps to provide good air circulation, reducing the humidity that can lead to late blight.

  3. Practice crop rotation: Avoid planting potatoes or tomatoes in the same area for at least two years to reduce the chances of the disease being present in the soil.

  4. Keep the garden clean: Remove and destroy any infected plant parts and volunteer plants to help reduce the spread of the disease.

  5. Water in the morning: Water the plants in the morning so that the foliage dries quickly and does not stay wet for too long.

  6. Monitor the plants regularly: Keep a close eye on the plants and monitor them regularly for any signs of late blight so that any infection can be addressed early on.

  7. Use fungicides: Fungicides can help prevent late blight, but they should be used as a last resort and only when necessary. It's important to read and follow the label instructions carefully.

By following these prevention methods, gardeners can reduce the likelihood of late blight affecting their tomato and potato plants.

Guide Information

Tomasz Klejdysz, Radovan1, Shutterstock

While every effort has been made to describe these plants accurately, please keep in mind that height, bloom time, and color may differ in various climates. The description of these plants has been written based on numerous outside resources.

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