People started seeing yellowing and browning needles a few weeks ago. Damage typically occurred in the upper portion of the plant but occasionally was all over. Many growers commented that they had been in the field just a few weeks prior to this and saw no problems, even tagging some trees, only to come back later to find major needle loss.
When you look closely, not every needle in a fascicle is affected. Sometimes there are bands of green and yellow tissue on the needles. Many growers also found that only the sheared white pine was affected. We only found one site where there were some unsheared white pines that also had the same symptoms.
When this occurred in 2007, the problem was diagnosed as Bifusella linearus, a needle cast found on white pines. We have sent samples off to look at a positive identification this year. However, it is often hard to diagnose needle casts. There are several fungi associated with white pine needles. And there is also confusion between needle casts and ozone injury on white pine.
Ozone damages plants by making the stomates sluggish. It is typically the fast growing trees and weeds that are affected most by ozone. The USDA website (click here for site) lists the following plants as good indicators of ozone damage along with the damage seen:
- Blackberry, secondary canes (Rabus spp.): Red to purple stipple.
- Black cherry (Prunus serotina): Red to purple stipple, may drop the injured leaves early.
- Common milkweed (Asclepias syriaca): Purple to black stipple, leaves may be chlorotic (yellow).
- Yellow-poplar (Liriodendron tulipifera): Brown stipple, may drop the injured leaves early.
- White ash (Fraxinus americana): Red to brown stipple. Similar injury is also found on green ash
So if you suspect ozone, look at these indicator plants nearby to see if there is also damage. White pines were taken off the indicator list in 1995. If these are not showing symptoms, it is most likely a needle cast.
This is also some question if fertility is playing a role. This time of year calcium deficiency is showing up in Fraser firs and white pines. If you are having extensive problems with needle loss, it might be a good idea to take some soil samples and plant tissue samples to further diagnose the problem.
No matter what is causing this damage, there is probably little a grower can do. One of the main reasons is that the profit margin is so low on white pines that it makes any fungicide treatment unattractive. However, when we get a positive diagnosis, I'll pass along treatment options.
Of course the main question is if the damage will continue to get worse this fall. In falls past it did not, so hopefully what we're seeing right now is the worst of it, and undamaged individuals will remain looking good. The following are some photos I took on Friday.
|Banding on the needles|
|Not every tree is affected and not all the same way.|
|On this plant, damage only occurs in the upper portion of the plant.|
|Another shot of banding.|
|This tree was affected overall.|