What to do about powdery mildew? Ask our grower

What to do about powdery mildew? Ask our grower
Luke Sholl

A common problem when growing weed is Powdery Mildew. But what can you do to solve and prevent this? We asked our expert grower.

Hello people from CannaConnection!

I am currently around week 4 of flowering. Everything looked great, but then I left the town for the weekend and I could not attend my plant throughout that time. When I came back I noticed something white on the surface of the leaves? Are my plants sick? Should I worry? Is there anything I can do about this?

Hoping you can help me out and with kind regards!


P.s. Love the website!

Hi there Andrew!

First of, thank you for the compliment ;). We always like hearing that.

So, about your plants. On the photo you provided you can clearly see Powdery Mildew developing on the leaf. If you encounter it at this stage of plant development, it is a sign that your fertilizer mix is missing some ingredients needed for plant resistance.

We would recommend washing the leaves with high pH water (around pH=8-8,2), some people use bicarbonate for this purpose, but be careful with the amounts you use if you go for it. You want to create an alkaline environment on the surface of the leaf as this should stop further spreading of the problem at least for now, but you will still need to improve your feeding schedule. 

We would recommend including some products which will provide more Calcium and Silicon (Si) to your plants. Both of these elements have structural functions in the plants and help with overall nutrient absorption. There are studies on fruit trees showing positive results in Powdery Mildew prevention just by using light solutions of Si in form of silicic acids etc. 

A too high humidity level is usually the cause of fungus. This is the main environmental factor which holds control over fungal infestation. Try to keep the humidity below 55% after the 3rd week of flowering in the future. In dry conditions it is harder to get fungal problems and also easier to eradicate them.

If the problem appears on few single leaves, you might consider clipping them and removing them from the garden as you want to be careful and not spread the spores around the grow area. This is why it would be best to turn off your fans before you do this and spray the plants a little with high pH water.

We hope things will work out for your plants, and that you will be able to prevent fungal problems in the future. 


Team CannaConnection

Luke Sholl
Luke Sholl

Fascinated by the wellness potential of nature, Luke has spent over a decade writing about cannabis and its vast selection of cannabinoids. Creating, researching and writing content for Cannaconnection, alongside several other industry-related publications, he uses strong technical SEO skills and diligent research to bring evidence-based material to thousands of unique visitors.