Virtually impossible.
I don't know about your customers, but I cannot count on my customers to know a juniper from a hemlock.
Everything around here is a "pine". Over the phone diagnosis depends on knowing what kind of tree it is.
" Does your tree have needles or scales"
Customer
I don't know. What is a needle?
(After a lesson): "how long are the needles"
"pretty long. How would I tell if they are scales?"
"Are they stiff & pointy, or are they soft"
"Can you tell if they are dying from the tips of the branches"
"Yes, the branches are dying all over"
2 minutes later I give up, never to return to that method of diagnosis. This could be a white pine with annual needle drop, a juniper with bagworns, an austrian pine with Diplodia, or almost anything else, including your rhizosphaera needle cast. Some borrowed diagnostic tips that clearly show how unlikely an accurate phone diagnosis are:
What kind of diseases affect blue spruce trees?
There are three principle types of diseases that affect blue spruce trees: needlecasts, tip blights and canker diseases. All of these diseases are caused by fungal pathogens and each produce specific symptoms that can be useful in diagnosing the problem.
1. Needlecasts. As the name implies, trees with needlecast diseases shed needles. Needlecast fungi often infect needles on the current year’s shoots. As the disease progresses, the needles die, usually the year following the infection. As a result, trees affected by needlecasts often have an outer “shell” of live needles on current shoots and dead needles on older shoots (Photo 3). The two most common needlecasts we find in spruce are caused by the fungal pathogens Rhizosphaera and Stigmina/Mycosphaerella.
2. Tip blights. Tip blights are fungal diseases that typically cause dieback to new, emerging shoots (Photo 4). Tip blights are most common on pines, especially Austrian pines, but can also occur on spruces.
3. Canker diseases. Canker diseases are caused by fungi that infect branches or the main stem of trees. Typical symptoms of cankers are sunken areas along a stem that may ooze resin (Photo 5). Trees may produce ridges of wound tissue around older canker infections as the tree attempts to restrict the fungus’ growth. As cankers develop, they can interfere with the branch’s ability to transport water and nutrients, resulting in the death of individual branches often referred to as “flagging.”
What kinds of insects affect blue spruce trees?
Numerous insect pests can impact spruces in Michigan’s landscape, but the two most common are gall adelgids and spruce spider mites. In both cases, the insect pests are tiny and you may need a hand lens to see them. Often times, people are more likely to see the damage as opposed to the insect pests themselves.
1. Gall adelgids. Adelgids are small insects that feed on shoots by sucking plant sap. As they do so, they cause the shoots to deform and produce galls that resemble cones (Photo 6). Damage from gall adelgids is mainly aesthetic.
2. Spruce spider mites. Spruce spider mites cause needle discoloration and eventually kill needles, which can be mistaken for a needlecast disease (Photo 7).