Powdery Mildew: Identify, Prevent and Treat White Powdery Mildew on Cannabis: Part 1 – Identification

Powdery Mildew and Growing Cannabis

“Powdery mildew” are the two words no cannabis grower ever wants to hear. If you’ve ever had powdery mildew while growing medical marijuana, you know it is like the herpes of cannabis plant problems and not one you want to have. If you’ve never had powdery mildew on your cannabis crop, then please congratulate yourself and read on for more information on preventing powdery mildew in the future.

If you are currently dealing with powdery mildew on your cannabis plants, have no fear! There are options for treating, and even eliminating white powdery mildew from your grow room or crop.

Let’s start off with some of the basics that we learned from doing research while battling this problem in the past.

What is powdery mildew:

If you are going to diagnose, treat, eliminate or even prevent powdery mildew on your cannabis plants, you have to first know what you are looking for – right?

First off, powdery mildew is considered to be a fungal disease caused by several different species of plant pathogens that thrive in different parts of the world and affect different varieties of plants. Powdery mildew is partially made up of tiny mycelia and spread by microscopic spores which travel mostly by wind and infect other plants once the spores land and later ultimately germinate.

The image above shows a heavily covered leaf that is severely infected with powdery mildew. It looks almost as though the leaf has been coated with white powder that looks similar to flour. While this is a very heavily infected leaf, many times you can spot powdery mildew when it is contained to a very small area and stop it in it’s tracks.

Powdery mildew, or PM as it is often called, is a fungal disease that affects many plants including the cannabis plant. Powdery mildew has many different species and the one that typically affects cannabis, which is cultivated for medical marijuana, is the same as the white powdery mildew species that attacks hops and even hemp in the wild.

Identify Powdery Mildew on Cannabis Plants

The following image shows an early break-out of powdery mildew. In this stage, you have a lot of hope in treating this disease. In this early stage, and even earlier, you can spot the patches of mildew starting to form. By giving your plants a regular visual inspection, you will notice issues before they become too serious.

Spotting powdery mildew in the early stages isn’t always easy. Sometimes all you have is a very small patch hidden in the crevice of a leaf. This is why I like to give a thorough visual inspection regularly and from different angles. By turning your head to the side and looking at the leaves of your cannabis plant from a side-view, you may just save your entire crop by spotting something you wouldn’t have otherwise seen.

Make daily visual inspections to all plants in your grow for the best chance of spotting a problem early. Doing so will help you keep issues like mold, mildew and pests at a minimum when they do show their ugly crop-destroying faces.

Now that we know what powdery mildew is and the signs to look for in our cannabis grow rooms, let’s talk about preventing it, and then treating it if your attempts at preventing powdery mildew fail.

In part 2 – we will discuss powdery mildew prevention methods, as well as treatment options if you do find yourself unlucky enough to catch a case of the PM blues.

For a great reference book on cannabis gardening, be sure to pick up a copy of:  “Marijuana Pest and Disease Control: How to Protect Your Plants and Win Back Your Garden by: Ed Rosenthal

Check out the great sources below for more information on powdery mildew identification, prevention and treatment.


“There are many different species of the fungal disease powdery mildew, and each species attacks a variety of different plants.”

Source: Powdery Mildew: How to Identify, Control, and Prevent Garden Diseases | The Old Farmer’s Almanac

“Powdery mildew may adversely affect flowering, plant vigor, and yields, although this disease rarely kills plants outright.”

“Symptoms include the presence of white, tan, or gray powdery fungal growth (mycelia and spores) on surfaces of infected plant parts”

“Powdery mildew is favored by temperatures between 68° and 77° F and humidity of 40% or more.”

“Caused by the fungus Golovinomyces sp.”

Source: Powdery Mildew of Hemp | Kentucky Pest News

“Powdery mildew is one of the easier plant diseases to identify, as its symptoms are quite distinctive. Infected plants display white powdery spots on the leaves and stems. The lower leaves are the most affected, but the mildew can appear on any above-ground part of the plant. As the disease progresses, the spots get larger and denser as large numbers of asexual spores are formed, and the mildew may spread up and down the length of the plant.”

Source: Powdery mildew – Wikipedia

“Powdery mildew spores can be transported to your plants on the wind, through air ventilation systems, from pets, and any other living thing that moves (including yourself). Until the surrounding environment is ideal, the spores from mildew will stay dormant, biding their time.”

Source: Stop Powdery Mildew On Marijuana Plants Now!

“Plants infected with powdery mildew look as if they have been dusted with flour.”

Source: Powdery Mildew: How to Identify, Control, and Prevent Garden Diseases | The Old Farmer’s Almanac

“This fungus is one of the most common to affect marijuana plants, it needs high humidity and a minimum temperature of 20ºC to be able to grow and sudden changes in temperature benefit its appearance. Although an infection of powdery mildew is easy to identify, and it does have a treatment, if a remedy is not used in time, the consequences can be fatal.”

Source: The most common fungi that can attack your marijuana plant

© CannabisChris.com 2016
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