Downy Mildew Control: How to Identify and Get Rid of Downy Mildews

Whether it is in the case of crops or ornamental plants, downy mildew can be a huge problem. Despite being a common disease, it is often under-diagnosed, and hence, a lot of people are unable to treat the condition before it escalates into a threat that is harder to handle. With the right knowledge, however, it will be easy even for novice gardeners to make sure that their plants will not have to suffer from downy mildew.

What is Downy Mildew? 

A lot of people may confuse this disease with powdery mildew. Although the names are almost similar, it is important to note that the two are different in more ways than one. One of the major differences between the two is that true fungus causes powdery mildew. In the case of downy mildew, on the other hand, the cause is not true fungi but parasitic organisms. The main culprit for downy mildew are microorganisms that belong to the genus of Peronospora or Plasmopara.

It is a foliage disease that can easily spread from one plant to another through airborne spores. Insects and rain can also be potential carriers of the disease, as well as garden tools that are contaminated. As a wet weather disease, the infection will easily spread during the times wherein plants have wet leaves. Moderate temperatures and high humidity are some of the external conditions that will be favorable for downy mildew. The spores will be more active in production if the temperature is cooler than 65 degrees Fahrenheit. Most of the time, the damages are only on the physical appearance, but in severe cases, it can escalate into a bigger problem, especially for commercial growers.

Downy Mildew

The damages are only on the physical appearance

Identifying Downy Mildew’s Damage 

Host Plants 

Downy mildew has a wide range of hosts, not only at home gardens, but even on agricultural lands. The pathogens belong to different species, each attacking only a specific group of plants. For instance, those that cause damage to brassicas are different from those that you will find in tobacco. Generally speaking, some of its most common hosts include brassica, tobacco, pansies, lettuce, onion, hebe, foxgloves, roses, peas, spinach, and rhubarb, among others.


Watch out for the following signs, which will give you an idea that your plants or crops may be suffering from downy mildew:

  • Discoloration on the upper part of the leaf is one of the signs you should look for. The color may be purple, brown, yellow, pale green, or gray, among others. They start out small but will get bigger if the plant does not receive treatment as soon as possible.
  • You will also spot a fuzzy substance on the top of the leaf or on the other parts of the host plant. It looks downy, which is where this disease got its name. Its color can be purple, grey, or white.
  • The host plants can also suffer from severe case of defoliation. Lack of vigor will also be apparent, which results from the lack of nutrients. 

Results of Infestation 

During the onset of the infection, most of the damages will affect the aesthetics of the plant. This is why it is a big problem for ornamental plants as it can make the garden or the landscape unattractive. Stunting is a common outcome of infestation, which is due to the inability of the plants to receive the nutrients that are essential for its survival. In the case of crops, commercial growers can suffer from an economic loss is the infestation is severe and if it is too late before acting on the problem.

Coleus Downy Mildew

Symptoms of coleus downy mildew on leaves

How to Get Rid of Downy Mildews

Natural and Organic Solutions

Thinking of the best ways to prevent and treat downy mildew? Below are some of the solutions that can prove to be promising:

  • Sanitation is one of the things that need your attention. Whether it is in a small garden or in a huge plantation, exert effort to keep the surroundings clean. Take off decaying leaves or vegetation. If there are plants that are already showing obvious signs of damage, take them out as soon as possible. Leaving it on the ground will make it easier for the disease to transfer to other plants.
  • The right choice of plants will spare you from frustration. Ask your local nursery for varieties or cultivars that can resist downy mildew, among other common diseases. Some of the best examples of plants to grow include all-star melon and Fanfare cucumber.
  • When planting, see to it that there is generous spacing in between each plant. This will help in encouraging better air circulation. It will be easier for the pants to breathe and they will be healthier. Plus, this also means that the disease will not easily spread from one plant to another.
  • It will also help to maintain the dryness of the foliage or the top part of the plant. This is because moisture will be an attractant for the pathogens carrying this disease. Therefore, rather than watering from the top, drip irrigation can be a promising alternative.
  • Watering is essential for the health of plants. Overdoing it, however, is bad. Do not water the plants at night. This will increase the level of humidity and will retain wetness of the leaves since the sun will not dry it out. It will be an attractive environment for pathogens. Instead, water early in the morning, which will guarantee that the leaves will dry quickly.
  • Crop rotation is another basic solution for downy mildew. Do not plant the same crops within a year or two. Alternate it with resistant plants. For instance, if you plant soybeans this year, look for another non-related crop to grow next year. 

Chemical Solutions

There are no chemical controls that will be effective in the treatment of downy mildew. While fungicides can be effective in the treatment of other diseases, this is not true in the case of downy mildew since the latter is not a fungal disease. With this, rather than using toxic products to get rid of the problem, keep an eye on the solutions above.

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