Sickly Spruce Trees

Brenda Rettinger

Bowman County Extension Agent

How do your spruce trees look? See any dead branches or an overload of brown or red needles? If you haven't checked, pencil it in your schedule. You may be able to save your precious trees from death.

According to Cheryl Biller, NDSU Plant Diagnostician, there are two diseases that are showing up at the lab already this spring. Rhizospaera needlecast and Cystospora canker both cause browning of needles and both typically start at the bottom of the tree.

In my travels within the Bowman County spruce population, I have sampled trees in the Scranton and Rhame areas who have tested positive for Cystospora. So far, though, I have yet to find a tree infected with Rhizospaera in this area. Let me explain these diseases to you.

Rhizospaera needlecast is caused by a fungus. The needles in the lower branches, nearest to the trunk are the ones that turn brownish purple and fall. The disease gets its name because the tree "casts" off its needles- often in the spring. Confirmation requires examining the green needles that are close to or on the same branches as the brown needles. If you get your private eye lens (magnifying glass), you can see small black structures that have filled the stomates (which normally appear white). It really looks like the needle has two rows of blackheads running along the length of the needle. The black spots are fungal fruiting structures which form spores that cause new infections. Rhizospaera can be controlled with two consecutive fungicide treatments 3-4 weeks apart and repeated for at least two years.

Cystospora canker is also caused by a fungus. When this disease appears in the tree, typically the bottom branches are affected first, but the browning starts at the end of the branches and proceeds back to the trunk of the tree. Please note, however, that I took samples from a blue spruce tree south of Scranton that was dying from the top down that tested positive for Cystospora. Needles generally turn a light tan to brown and may remain attached to the tree for a year or two. You may often see sap being extruded from infected branches. It appears as a sticky, white or bluish white ooze on the infected branch or on branches immediately below those branches. Research shows that drought- stressed trees are more susceptible to Cytospora. Fungicide is not effective with this disease- it must be managed by careful scouting and pruning. Any branch with browning should be removed, as well as a few branches above the infected ones. Obviously, it is important to know that your trees have Cytospora before you go hacking down half your beautiful spruce trees!

If you think your trees may have one of these fungal diseases, you can give me a jingle and I can dissect a sample and send it to the lab for analysis. There are several conditions that are basically harmless to your spruce trees that may easily be confused with more serious conditions, so don't be bashful about asking. The most important thing is to monitor your trees so you have an idea of where and when any funky conditions start. Trees are a priceless addition to our homes!