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Powdery Mildew

Powdery Mildew
is caused by the fungus Podosphaera Macularis.  This is not a fungus brewers should take lightly because it can cause severe crop damage and may result in lost production and minimized cone quality.


The fungus appears as small, circular, white to silvery-white powdery colonies on the hop leaves, buds, stems and cones.  As the fungus spreads, the colonies increase in size from about 1/16 inch to 1/2 inch or larger.  When the mildew is spread to the female flower or cone it becomes very serious and can cause yields to drop 80% or more.  Infestation in early stages of the female flower may cause the cone to never develop or it can become deformed and brittle as it forms.  Some affected cones may show the white powdery fungal growth, but in other cases it may only be visible under a microscope.


Conidia, air-borne spores are released from the fungal colonies and carried by the wind for miles.  Newly-formed infections produce the conidia in 96 hours.  The fungus strives on high humidity and temperatures between 55°F and 90°F.


Begin in early spring by removing all green tissue during spring pruning (even shoots on the side of hills).

Apply first fungicide as soon as shoot growth resumes after pruning.

Try our organic mildew and fungicide solutions.  Easy to use and listed OMRI. 

SaferGro Mildew Cure Concentrate (16 oz)
Safer Brand 3-in-1 Garden Spray RTU

Note the white, circular colonies.
Photo by Cynthia M. Ocamb, 1998.
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Hop cones affected by powdery mildew. 
Cone development is stunted, and malformations may be evident.
Photo by Cynthia M. Ocamb, 1998
 Resources Click Here

Need more help?  Email us some pictures and we will try and help!

Here is a handy Pest and Disease Guide
Developed by
Oregon State University
University of Idaho
USDA Agriculture Research Service
Washington State University