A Basic Powdery Mildew Guide for Growers
If you have been gardening for any length of time, indoors, outdoors or most certainly in a greenhouse, there is a good chance you have seen powdery mildew the white mould on plant leaves. This is a plant disease that causes lots of losses around the world in a huge range of crops, whether being grown for food, fibre or medicine. Sometimes growers get Powdery Mildew confused with Botrytis (AKA “The Grey Ghost”). While both can ruin your crop if left unchecked, they are very different. For one, powdery mildew is a fungus-and Botrytis is a bacteria. In Tsung-Tsu’s “Art of War” one of the commandments is to Know Your Enemy. Once you understand what’s infesting and bothering your plants, ie the nature of it, what it likes and doesn’t like, you have halfway won the battle already. Let’s have a quick and effective lesson in identifying, preventing and treating powdery mildew, as it pertains to hydroponics, horticultural or greenhouse crops.
Usually you’ll see a very light white “spot” first, typically on dark, well fertilized foliage first. It will almost look like somebody spilled some milk or other white organic liquid onto a plant leaf and left it there to dry. As the disease progresses, entire leaves or even flowers get covered, looking like they have been dusted in a fuzzy looking all white icing sugar–but don’t be fooled, this stuff is anything but sweet to you and your crop! This is how powdery mildew or Erysiphe graminis is able to take ahold-it looks rather benign, or not that big of a trouble. That is, until your crop is ruined because it is a covered in this white mould.
If left unchecked, young plants that get infected will perform poorly, and in some plant varieties may not even flower, ie plant growth points succumb to being overwhelmed with the disease. Typically, while yields are affected negatively, the biggest damage or even loss comes from what the disease does to Crop Quality. In some plant varieties it makes the harvest completely unmarketable-ie, upon inspection, nobody will want it, nor should they.
Conditions that Favor P.M.
Humid and warm weather favors the development and spread of the this crop disease (15-24 Deg C). If it’s cooler, the disease spread is slower. Development and spread is suppressed by conditions over 30 Deg C.
Why Did My Crop Get P.M?
First, determine how bad the problem is and how far along the crop is. Is it better to simply terminate a young crop and start a new one after some scrubbing and precautions? I
Types of Treatment
A Note of Caution:
Moulds of all kinds can be hazardous to your health if inhaled-some causing serious or even potentially fatal respiratory issues via the lungs. Make sure you aren’t breathing in spores, indoors or out and dispose of diseased plant materials right away-incinerating is the best, and can feel the most satisfying too.
Erik Biksa has been writing about and discussing hydroponics growing, related technologies and cropping methods since 1999 in a variety of professional publications and platforms globally Erik has travelled the world learning and teaching modern growing techniques and technologies and is appreciated by many growers for his informative yet hands on approaches. Presently, he is the Editor at Grozine Hydroponics Mag.