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Home > Plant Diseases > Downy Mildew on Hops

Diseases of Hops: Powdery Mildew and Downy Mildew are serious diseases of hops and can totally destroy a hop yard. For instance, throughout the mid to late 1800's, upstate New York State was the hop growing capital of the country, producing millions of pounds of hops. In the late 1800's, however, Downy Mildew (sometimes spelled Downey) infected hops yards throughout New York. Efforts to fight the disease were not successful and hops farms went out of business. [1]

Downy Mildew: Downy Mildew thrives in damp conditions with temperatures in the 60 to 70 degree range. [2] The optimum temperature for spore germination is 65 degrees F and the spores will germinate within 4 hours in a film of moisture on leaves. [3] Downy Mildew will affect all parts of the plant from the roots / rhizomes to the hop cones. In more mature plants, Downy Mildew will appear as grayish spores on bottom surfaces of leaves and ultimately result severe leaf necrosis (black and brown spots, curling and leaf drop). At this point, the disease can be controlled by a foliar fungicide such as GreenCure Fungicide. As a foliar fungicide GreenCure is an important component of your Integrated Pest Management (IPM).

Disease Prevention & Control: GreenCure Fungicide is proven effective against diseases of hops including downy mildew and powdery mildew. GreenCure is OMRI listed and EPA / USDA designed for "Organic Production / Gardening". GreenCure is a potassium bicarbonate based fungicide that is effective against 25 plant diseases on more than 150 plants including ornamentals, herbs, fruits, vegetables and of course hops. GreenCure was developed by renowned plant pathologist, Dr. Ken Horst at Cornell University. By combining potassium bicarbonate with special surfactants that spread and stick the solution to plant surfaces, the GreenCure formula creates a synergy of action against fungal diseases. GreenCure splits open fungal spores and dehydrates the spores effectively killing the mildew and breaking the fungal life-cycle.

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How to Use GreenCure: GreenCure is a powdered product that is mixed with water at 2 tablespoons per gallon of water. (For tank mixes see chart below*). Shake well. GreenCure should be applied with a pump or pressure sprayer with a fine mist spray nozzle. Spray to cover both tops and bottoms of leaves as well as the bines and cones. Do not saturate to the point of dripping. As will all spraying, it is best to spray in the early morning or late afternoon out of direct hot sunlight to prevent scorching.

Prevention is the Best Course of Disease Control: GreenCure can be sprayed early in the season and throughout the season up to harvest. With all plant diseases, prevention is better than trying to control an active infestation. Spray GreenCure as a preventative. Downy mildew can develop in as little as four hours under the right conditions so maintaining a thin coating of GreenCure can prevent spore germination. Spraying can be done when environmental conditions are good for disease development and as often as every 7 to 14 days.

Use GreenCure at the End of the Season: Downy Mildew will overwinter in the bine stubble and rhizomes. If this occurs it will become increasingly difficult to control the disease next year. After the bines have been cut and removed from the hop yard and the plants are trimming back with clean clippers the above ground roots, and stubble should be sprayed heavily with GreenCure. While GreenCure is not intended as a root drench it will work against the residual spores on the exposed plant surfaces. Dead leaves and bines should be removed from the hop yard and preferably burned or landfilled.

Check for Disease at First Sign of Plant Growth: According to the "Alternative Field Crops Manual" published by the University of Wisconsin Cooperative Extension, "The first symptoms of the disease appear in early spring when a part or all of the new shoots arising from a hill may be infected. Badly infected shoots are unable to climb and are stunted, brittle and lighter in color than healthy shoots. These "spikes" are infected internally by the fungus and may carry millions of spores. The spores can be carried by wind or water to other shoots and can infect the tips of healthy shoots." [2] If disease symptoms are showing early if will be vital to lightly spray the new shoots with GreenCure. It may also be wise to test a systemic fungicide that can enter through the roots. If the disease is showing early control could be quite difficult.

* Mixed at 2 Tbs. Per Gallon of Water
1.75 Lbs. (1/2 40oz. Container) = 20 Gallons
2.50 Lbs. (1 40oz. Container) = 40 Gallons
5.00 Lbs. (2 40oz. Containers) = 80 Gallons
10.0 Lbs. (4 40oz. Containers) = 160 Gallons


  1. "The Past, Present and Yes, Future of the Hops Industry", Upstate Alive Magazine. (Cooperstown, NY) 1996, 1:4 by Richard Vang.
  2. "Alternative Field Crops Manual" published by the University of Wisconsin Cooperative Extension.
  3. GreenCure Fungicide Plant Diseases: Downy Mildew (Content from Plant Pathologist, Dr. Ken Horst.

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