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Question from Wendy, South Jordan, UT (received 4/30/20) -
I have an Austrian pine that is turning yellow throughout the whole tree green and yellow mixed needles. It is 25 years old. I lost one three years ago, acted same way, had no sap tunnels or burrowing sign or holes in bark. Saw no sign of that on the one we like at before either. What can I do I have many of these same trees on my property?
Wendy Penrose
Answer from Dr. Mike Kuhns, USU Extension Forester and Professor (sent 5/5/20) -
Wendy,
I can see from your photos that this tree is quite unhealthy. What is most unhealthy looking is the absence of needles. There are some needles but only the newest ones remain on the tree. There should always be at least 3 years-worth of needles on an evergreen conifer like a pine. The newest needles are near the tips of the branches and the oldest ones are farther back down the canopy. Every year the tree branches elongate from the buds in the spring, needles grow out as the branch grows, and a year’s worth of needles (the ones that are farthest in on the branch) die each fall. Though the tree is an evergreen because it always has green needles on it, the needles are not evergreen.
Your tree has lost most of its needles that are older than one year, and the fact that even many of those needles are brown half way down their length is that much worse. And worse still, what live needle material is on the tree is yellow, not dark green as it should be.
I suspect that there is something wrong that involves the soil and the root system, so it would be good for you to dig around the base of the tree and see what you can find, while avoiding injuring woody roots as much as possible. A good way to do this is to use pressurized air to blast away the soil at the root collar, which is where the trunk meets the soil. However that requires the use of an airknife and a large compressor that I am guessing that you do not have. A slower alternative is to loosen up the soil near the root collar and vacuum it away with a shop vac. What you should look for is woody roots that are growing around the trunk base (girdling roots), a deeply buried root collar caused by planting too deep, or something with the soil itself (too wet, extremely compacted, etc.). If you do this, take some photos and send them to me.
Another thing to look at and to take photos of is branch growth for the past 10 years or so. A tree that is becoming as stressed as this one is will have slowing twig growth, and observing that growth can tell you a lot. To measure this growth you just start at the tip of as healthy a branch as you can find on the tree, then go back along the branch and find the point where the terminal bud was 1 year ago and measure the distance from the tip to that point. The way to find this point is to look for a change in appearance of the twig or branch bark, to look for linear scars that circle the stem where the bud scales were attached to it, and often you will have small twigs that branch off of the bigger branch at that same point. Then go back to where the terminal bud would have been 2 years ago and measure the growth from year 1 to year 2. Do this as far back as you can go. On a pine it is pretty easy to go back 10 years or more, and often you can actually age the tree if you go back to the limb and then the trunk and finally the root collar. There is a good chance that whatever is wrong with the tree has been developing for a long time, and doing this will tell you when the problem started by when the growth started to slow down, how abrupt the change in growth was, and whether it is getting worse recently.
Good luck.