Powdery Mildew (PM) (Fig 1) is another potentially prevalent disease that hops can contract. It has not been seen too extensively yet here at MVH, perhaps due in part to small hop acreage and plantings of more disease resistant varieties, but this pathogen has the potential to be as problematic as Downy Mildew (DM).
Unlike DM, PM can infect both the undersides and tops of leaf matter to include cones and burrs. While DM tends to start at the lower leaf matter and work upwards on the bine, PM can infect any portion of the bine equally. Fortunately, it has not been shown yet that PM can become systemic inside the plant tissue.
PM first appears in the spring as “flag” shoots (Fig 2). Just like DM, these shoots appear stunted and need to be removed from the hop yard. Favorable conditions for the disease are 50°-85° with 65°-75° being ideal and high humidity with cloudy weather. PM can easily be spread to leaf matter or cones during these conditions.
Controls for this disease are numerous in both organic and synthetic forms. However, it appears that organic controls on PM are more effective than organic controls used on DM. Some of the organic controls for PM include Neem oil, Potassium Bicarbonate, Vinegar mixes and even milk.
(Fig 1) PM can be found forming a clump-like pattern on the leaves
or following the leaf veins
(Fig 2) PM flag shoot
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