I have four Wichita Blue Junipers planted about 8 feet apart along my driveway in full sun. I planted the Junipers about 12 years ago and they are about 12-14 feet tall. I noticed that all four are browning from the top to bottom of the trees. What can I do to reverse the browning?
While I can provide you with some information about juniper diseases and pests, as all of your trees are affected and they are a considerable size, I suggest that you consult an arborist for a definitive diagnosis so that you can deal with this matter quickly and, if possible, bring the trees back to health. The arborist would also advise you as to the most appropriate treatment that might be needed to deal with the problem.
Junipers (including yours, Juniperus scopulorum ‘Wichita Blue’) are susceptible to a few diseases, particularly to blights when spring has been unseasonally rainy or wet. One of these is phomopsis twig blight.
Penn State Extension has published a good overview of “Juniper Diseases” – including phomopsis twig blight. Clemson Cooperative Extension is another helpful resource: see “Juniper Diseases & Insect Pests”.
This may be a fungal disease, as described in Cornell University’s “Juniper Tip Blights” — fungal diseases are characterized by dying-back of twigs and branches, and usually show up initially on recent growth in lower branches, progressing from the shoot tips back towards the main stem [this does not sound like the progression you describe, but as fungal infections are a concern in junipers, you should be aware of this possibility]. The authors note that there may be other causes of these symptoms, including drought, freezing, and dog urine. Prune off all affected twigs and branches, at least 2 inches into live wood – and dispose of these (don’t compost them).
As well, spider mites may also attack junipers, causing a yellowing or browning of the trees and death of leaves and twigs. They will produce a coating on the twigs (which is a fine webbing that collects debris blown in the air). New Mexico State University’s “Spider mites on junipers” provides details on these pests. Spraying the trees with strong jets of water every few days should get rid of the mites. If this does not work, you may need to resort to chemicals.
And finally, as your trees are planted along your driveway and it’s been a very cold and long winter, I wonder if you salted the driveway and mounded up snow against them? Many evergreens have been affected by snow and salt this year. If so, you could also try irrigating the ground to leach out any salt that may still be in the soil. Good luck!
https://www.botanicalgarden.ubc.ca/forums/showthread.php?t=3976 “If your Juniper starts to turn brown in areas of the exterior of the plant, then use a copper or calcium based fungicide as a treatment. You may get what may appear to be a rust like disease in the interior of the Juniper but most of the times, in cooler climates, that is due to lack of sunlight. I doubt it due to your climate but it is possible I guess that you can get what bothers us the most and that is Mite damage. Many people here equate the rusting in the shaded areas in the interior of the Juniper to be a disease when for us it generally is an indication of a probable Mite or Spider Mite infestation.”
Missouri Botanical Garden. “Juniperus scopulorum ‘Wichita Blue’” https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=c211