Blue Star Juniper leaves turning yellow in the interior of plant -- is it dying?
I believe I have a blue star juniper (its maybe a foot high and several feet around) and recently I noticed the interior leaves turning yellow all over the plant. The exterior is still blue-ish but I am worried that the yellowing indicates it may be dying? The other possibility is that yellowing is a response to the hollytone fertilizer I gave it back in March - may a cupful spread around the dripline?
I have had the plant for 2 years now. Last year, this did not happen but I also did not apply fertilizer. The plant is in full sun and gets watered once a week.
Deschutes County Oregon
Thank you for your question. First, as to whether the Holly-tone fertilizer is the culprit, I don't know whether you followed label directions, but it seems unlikely, if you did, that this is the cause of the yellowing. Second, there is a blight that infects junipers, which can't be diagnosed without a close examination of the stems. Finally, since this cultivar (variety) of juniper is not listed in the OSU susceptibility chart, I can't tell whether yours has any particular soil pathogen issues.
I suggest that you take your photos and some clippings of the yellowing/browning leaves, and visit your county Extension office, whose contact information is found on this web page. They have access to a microscope, and can help identify the problem and suggest controls, if available. Good luck!
It turns out my juniper is a blue chip juniper, Juniperus horizontalis. IIt is listed on the OSU susceptibility chart you sent me but the row is blank! What does that mean about its susceptibility to those blights? Susceptibility is unknown?
The reason the row is blank is that the subspecies members are listed underneath is (it's like an umbrella for the varieties below.) Here is a link to what the OSU plant disease manual says about this species' vulnerability to phytopthora However, this UConn Extension article indicates your plant is more susceptible to a different pathogen, Phomopsis, which is described here. This is the blight that I referred to in my first response. It has been detected in junipers, and the difference between the two is described here. I think this amply illustrates why it is helpful to have a diagnostician who can examine plant tissue before proceeding further.
Thanks again. I will take a sample to the Extension office.