As most growers are aware, downy mildew is extremely active in Ontario hops this year due to the ideal conditions for development of the disease. For new growers, an article on identifying symptoms of this disease can be found in this blog post (https://onspecialtycrops.wordpress.com/2014/06/03/identifying-downy-mildew-in-hops/). Although some areas of the province have dried up somewhat, it is still important to continue sprays of preventative fungicides, as the disease can easily spread to the cones. Given the high levels of the disease across the province it is important to continue with sprays to protect developing bracts before cones close up.
For conventional growers, rotations of Zampro (ametoctradin + dimethomorph – Group 40/45), Torrent (cyazofamid – Group 21) , Revus (mandipropamid – Group 40) and Copper 53W (copper sulphate – Group M) should be continuing on a 7-10 day interval. In areas of the province that are drier and have less active infection, it may be possible to stretch the application interval longer, Organic growers have more limited options for control of downy mildew. Copper 53 W is likely the most effective organic product, but is limited to 4 applications per season. This can be rotated with Regalia Maxx and Serenade Opti, however both of these products are labelled for partial suppression only of downy mildew. Continue reading