Posted By Tom Farin on 04/12/2008 9:47 AM
Thanks for all the help.
Mike, I'm curious as to why you feel that burn on the very top shoot is a sign of impending death. It is a very common practice in the Christmas tree industry to clip the vertical terminal shoot of Firs as well as the end of their longest lateral shoots in order to retard vertical growth and encourage them to fill out. If the problem is the cells in the needles drying out in the extremities due to wind, how would clipping the dead ends result in a significantly different result than clipping the ends on a healthy tree? Everything I'm hearing indicates that if my problem is wind burn, the problem is localized not systemic. On the other hand, if the problem is spider mites, then I could understand that the whole tree is likely to die because the problem is systemic. And death might start at the top of the tree. But then if the problem is spider mites, I would expect to see brown all over the tree. On these trees, the brown side is consistently pointing in the same direction. Also, the lower portions lf these trees were covered by snow most of the winter. It's the upper portions that are damaged - indicating the problem is most likely to be wind burn. Not only that, the trees on the outside of my woods are more affected than the trees on the inside. I'm not challenging you here, just asking for clarification.
Good points...and the simple answer is "I'm not sure". I'm not a botonist. I have not seen wind burned trees the way you describe...but I've seen many ones that had mites and or were under irrigated. Regarding mites, they don't take over the whole tree at once. They "eat" their way into the tree...often from the side or on lower branches. If not treated, they infect the whole tree and just suck it to death...and often cause other diseases to take hold...as the tree weakens.
Mite infected non-deciduous trees often show localized damage...that's where the infestation is most severe. Side to side, bottom to top...it moves as the bugs eat their way into the tree.
As for "tip death" (that's what it is called here), I don't KNOW the mechanism that makes this a death indicator...other than the fact that the "disease" has climbed all the way to the top. That may be why my experience is that pruning doesn't help...the disease has simply spread too far...and the plant is "terminal". As mites progress through a tree...they eat their way into the center...and up...looking for the moist, softer wood. So, by the time they get to the top, they've very much compromised the ability of the tree to distribute moisture to the wood and "leaf" cells. This is why my arborist explained to me to use a systemic insecticide...you need to kill the mites INSIDE the body of the tree...and I know it really works.
As for why Christmas trees can be trimmed....simple, they're heathly. As an example, surgical removal of a human's hand won't kill a human either...unless the surgical area gets infected...or is infected. Basic health is important.
It's the same for plants...the dead, dried out area is the sign of death or impending death of that localized part of the plant...but the infection (the mites) is elsewhere...still growing..and pruning won't treat that.
I would THINK (don't really know) that plant distress caused by under irrigation or wind is similar to the dehydration caused by mites. If water doesn't get to the plant cells, those cells die. And the parts that are obviously dead are NOT showing the whole region of distress. As with the mites...other more central parts of the tree are also affected (versus infected)...and are dying.
From what you've shown and explained, I'd agree with you that wind burn sounds more like your problem...unless the trees ALSO had mites...which would just make the wind burn symptoms worse. If it were me, I'd think about how I'd keep them from becoming dehydated in your area...and that might mean wrapping them in burlap if they're NOT protected by snow.
Lastly, remember these are spruces...NOT pines. Spruces live on the lower slopes of mountains...not on the upper slopes where pines flourish...and my GUESS is that's because there's a hydration difference between trees huddled together down low in a forest where other trees protect them from wind....and those that can stand more wind up high. Spruces seem to need more protection...while pines don't.