Debra from Rochester, Mi writes
Prime Source Chlorothalonil 720 Select is labeled for rhizosphaera but is usually not recommended. Most Chlorothalonil based products are actually specifically labeled against use on blue spruce because they turn the trees a very unsightly white color. This is unfortunate since most online articles and local master gardeners point you specifically to Chlorothalonil based products. Because none of the products are actually labeled for blue spruce we cannot recommend you use them on these trees. If you do choose to use one, we highly recommend you choose a product that lists rhizosphaera as a disease it treats on the label. We apologize we could not be more helpful!
Answer last updated on: 03/14/2016