|I took samples of one of your diseased yews to University of IL Extension program for opinion. They were surprised that they could not identify the fungus, but was sure it was not a parasite. The bush started turning a shiny deep reddish brown on the tips and spread to the middle. What type of fungicide would be appropiate for this type of disease, and do I have to cut it back.
|If the fungus is non-parasitic, it means that it is a secondary problem, that it is not living off your yew, but off of something that is feeding on your yew or off of the excrement from whatever is feeding off your yew. I'm surprised this was not explained to you during the diagnosis at U of IL. Mites are known for turning foliage a reddish brown during a feeding frenzy so I suspect there are mites present on your yew. Fungicide will not control mites (and once you control the mites, the fungi will die off, too). There are miticides on the market that you can use, but you might also be able to control the population by simply pruning off the affected stems and branches and disposing of them. Mites really like hot, dry locations so try hosing off your yews every week or so during the hottest summer months to discourage mites from taking up residence.
Best wishes with your landscape.