Mastering Disease Management: Powdery Mildew in Leafy Greens

leafy greens

By Karla García, Hort Americas Technical Services

Disease management in both traditional and controlled environment agriculture is as old and complex as the practice itself. In controlled environments disease can spread quickly and lead to significant losses if not properly managed. This first installment of our mastery series discusses how to recognize, control and prevent powdery mildew in leafy greens. 

What is powdery mildew?

Powdery mildew is a plant disease recognized by infection from different fungi species: Golovinomyces cichoracearum, Erysiphe, Microsphaera, Leveillula, Sphaerotheca, Uncinula, Phyllactinia and  Podosphaera. Usually infections are crop specific. In most cases of powdery mildew in leafy greens, such as lettuce, the culprit is Golovinomyces. 

Powdery mildew is a very common disease and the symptoms in leafy greens and can be recognized by gray to white powdery spots in plant leaves. Usually older leaves will be the first ones to show symptoms leading to chlorosis and deformities.

How can I get powdery mildew?

Powdery mildew can be triggered by warm temperatures, high humidity, poor airflow and low light levels and can be problematic in zones with dense canopies. When indoor farming is not properly managed, the environmental conditions can promote powdery mildew.

 By applying good cultural practices, powdery mildew can be avoided or easy to control. Some recommendations to avoid powdery mildew when farming indoors are:

  • Keep your crop in a relative humidity levels between 50 – 70%. Optimum humidity levels to promote germination of spores of powdery mildew fungi are between 95% to 98%.
  • Check out the specific recommendations of plant density for the leafy crop you are growing. High density can create conditions to develop powdery mildew. 
  • Sanitize all your equipment before and after every cycle. You can use hydrogen peroxide (3%) or bleach. There are also other products on the market such as Sanidate 5.0 that can be used to sanitize non-porous surfaces between crop cycles.
  • Maintain good air flow between 0.3 to 1 m/s. Make sure all zones in your crop are ventilated. 
  • Select varieties less susceptible to powdery mildew pathogen.
  • Examine the upper and lower side of leaves regularly to check for any presence of powdery mildew.
  • Harvest all your plants on time.

Photo by Beth Scheckelhoff, Ohio State University Extension.


(PLEASE READ THE MANUFACTURERS LABEL BEFORE APPLYING.  Check to make sure you follow label rates and only apply on crops and in applications that are permitted for use at your location before applying.)

You can also prevent or control powdery mildew using different pesticides with active ingredients like: Bacillus amyloliquefaciens strain D747 present in the product Double Nickel LC Biofungicide. Bacillus subtilis present in the product Companion® Biological Fungicide (For use in organic production). Myclobutanil is present in the product Eagle 20EW Specialty Fungicide. You can find these products available on our website!

Please reach out to a Hort Americas team member for a consultation or any questions you may have about our product offerings. We have the solutions you need to master your controlled environment operation.

Karla Garcia, Hort Americas Technical Services