This is important to consider, because Downy mildew is prevalent everywhere and can destroy your entire hop crop if not managed and controlled. Grape growers face a similar situation and have developed very effective control strategies. Hop growers will need to do the same.
Many hop growers do not understand the importance of controlling downy mildew in their hop yard after harvest is completed. The fungus and the infection are not as visible because there are no new shoots or infected spikes to be seen. Many growers consider the season as finished and leave the yard unattended going into winter. IMHO this is a fundamental mistake in controlling Downy mildew in hopyards. Downy mildew is active whenever conditions permit – it simply doesn't care if it is springtime, summer, or fall. (The 2014 growing season attests to that.) Post-harvest fungicide applications and controls can be the most effective way to manage downy mildew in yards that have had the disease present and reduce the severity of downy mildew spikes during the following spring growing season.
Downy mildew, like most molds and mildews, persists and spreads during the growing season mainly through air-borne spores which infect new leaves and growth whenever environmental conditions are favorable. In the Fall season, however, downy mildew “morphs” into a different creature; producing a specialized spore type called a zoospore. This spore acts much more like a living microscopic worm than a fungal plant-like spore. The zoospore form helps downy mildew complete its annual life cycle by finding a safe resting place for it to overwinter or by forming protective oospores; where it will be protected from the harsh winter that is ahead. This is a high-risk period for the downy mildew organism – it is outside its host and can be attacked most easily at this point.
Lynn, the head hop grower at Great Lakes Hops has over 30 years of experience in the horticultural field. Browse the blog articles here to find useful growing information for humulus lupulus, based on personal experience and observations at Great Lakes Hops.