Alphabetical Plant Listing

Downy Mildew

How to Identify, Prevent, and Treat Downy Mildew

What is Downy Mildew?

Downy mildew is a type of fungal disease that affects a wide range of plants, including vegetables, fruits, and ornamentals. It is caused by several species of fungi in the genus Peronospora, and it is characterized by yellow or brown spots on leaves, as well as a white, downy growth on the undersides of the affected leaves. The disease can cause leaves to become distorted, yellow, and eventually drop off, leading to reduced plant growth and yield. 

How to Identify Downy Mildew?

Symptoms of downy mildew can vary depending on the plant species, but common symptoms include:

  1. Yellowing or chlorosis of leaves, especially on the upper surface.

  2. Lesions or brown spots on the leaves - stems, and petioles are unaffected.

  3. Leaf curling, distortion, and stunted growth.

  4. White, cottony, or downy growth on the undersides of leaves may be accompanied by a purplish discoloration.

  5. Necrosis or death of leaves and shoots, leading to defoliation.

  6. Reduced yield, fruit quality, and plant vigor.

If you suspect your plants are affected by downy mildew, it's important to take action as soon as possible to prevent the spread of the disease to other plants in your garden.

What Causes Downy Mildew?

Downy mildew is a leaf disease caused by a fungus-like organism called Oomycete. It spreads from one plant to another through airborne fragments. This disease thrives in wet weather conditions, as prolonged leaf wetness provides ideal conditions for infection. High humidity levels, poor air circulation, and over-watering can all contribute to the development of downy mildew on plants.

Downy Mildew vs. Powdery Mildew

Downy mildew and powdery mildew are two common plant diseases, but they are caused by different fungi and have distinct symptoms and characteristics.

Downy mildew is caused by the Oomycete pathogen and is characterized by discolored blotches on the upper leaf surface and a mold-like growth on the underside of the leaf. This growth may be white, gray, or purple and is easily visible in some plants but not in others. Downy mildew requires high humidity and long periods of leaf wetness to infect plants.

Powdery mildew, on the other hand, is caused by Ascomycete fungi and is characterized by a white, powdery growth on the surface of leaves, stems, and flowers. The growth is easy to see and can be rubbed off with your fingers. Powdery mildew prefers warm and dry conditions.

Both downy and powdery mildews can cause stunted growth and decreased vigor in plants, but they are treated differently. Preventive measures, such as providing adequate air circulation and reducing plant stress, can help prevent both diseases. In severe cases, fungicides can be used to treat infections.

How to Prevent Downy Mildew?

There are several ways to prevent downy mildew from infecting your plants:

  1. Proper plant spacing: Ensure that plants have adequate space for air to circulate, which will reduce humidity and slow the spread of the disease.

  2. Appropriate watering practices: Avoid watering from overhead, which can wet the foliage, and instead water the roots directly. Avoid watering in the evening, as the leaves will remain wet overnight and create a conducive environment for the growth of downy mildew.

  3. Use of resistant varieties: Choose plant varieties resistant to downy mildew, as they will be less susceptible to infection.

  4. Removal of infected plant material: Remove and dispose of infected plant material as soon as it is identified to prevent the spread of the disease to other plants.

  5. Avoid overcrowding: Overcrowding of plants can increase humidity levels and provide an ideal environment for the growth of downy mildew.

  6. Crop rotation: Practice crop rotation to reduce the build-up of fungal spores in the soil and to decrease the chances of successive crops becoming infected.

Guide Information

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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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