The Value of Christmas Trees

"...there is no reason why the joy associated with the Christmas evergreen may not be a means of arousing in the minds of children an appreciation of the beauty and usefulness of trees; and keen appreciation of the beauty and usefulness of trees is a long stop toward the will to plant and care for them (Arthur Sowder, US Forest Service, 1949)."

Thursday, December 9, 2010

Needle Drop in Scale Infested Trees

This week I finished taking data on the needle drop in cut branches from scale infested trees. I reported on the experiment on November 10th when I set it up. The experiment worked worked well in that there was needle drop, but since there was too much needle drop, I guess it worked a little too well!

Many of the needles shattered as depicted in the photograph to the left. On some branches, almost all the needles fell off. That is definitely not something we're used to seeing with Fraser fir. If you look closely at this photo, you can see that this was from a scale infested tree, but the uninfested trees were just as likely to shatter -- just not as badly.

The room that the branches were stored in was very hot. It's an unused room at the Mountain Horticultural Crops Research Station office, and both Jeff Owen and I had shoots stored there. They kept the door shut and the room, which faces the sun, would often be too hot to be comfortable in. The shoots in the buckets faired the worse, dropping many needles. The shoots that were were kept dry kept almost all of their needles to the end of the study, but they dried out and became very brittle.

So did scale infested trees drop their needles more than uninfested trees? The quick answer is, "Yes." The results are summarized in the following table which lists the average percentage needle drop for all 15 trees in each group (infested and uninfested) for both the trees stored with water (wet) and without (dry). On average, 43.1% of the needles on scale infested branches had shed their needles while only 27.8% of needles on uninfested branches had shed. Also note in the table that there was more needle drop in the field on scale infested trees (first column labeled "From Field"). I had reported this back in November.

If you look at individual trees, by the end the experiment 47% of the infested branches in water had shattered a third or more of their needles (much like the photo above) while only 27% of the uninfested branches had more than 1/3 needle drop. Of course, that is much more needle drop than would be expected from cut Fraser fir. Remember that these branches spent less than 24 hours without water. Needle shed should have been at a minimum, and was through the first couple of weeks. Only one tree shattered its needles in week 2, and that was a scale infested tree. But by week 4, there were needles everywhere.

If you are a very perceptive observer, you will also note in the table that I only report on 1st and 2nd year needle drop and not 3rd as I said I would do back in November. That is because some of the 3rd year needles were under water in the bucket, and I didn't trust the results from them. In this photo, taken in week 2, the discolored needles had been underwater. These were more likely to fall off.

Generally results were along the lines I anticipated -- more needle shed in scale infested trees -- but the data were far from pretty. After all, there were uninfested branches that totally shattered their needles, and there were scale infested branches with very little needle shed. There were trees where one branch placed in water shed their needles, and the other branch from the same tree also in water hardly did at all. On about half of the scale infested trees, of the two branches taken, the one with more scale had less needle drop. So, I am not real happy with the results. I think I'll repeat this experiment next year either in January or next harvest season to see if I can get some clearer results.

I do think I can safely say the following: there appears to be slightly more needle drop in infested trees. However, needle drop occurs for a variety of reasons, and scale infestation is definitely not the over-riding factor. Still scale infested trees are messy. The scales themselves drop off as the tree dries out. There also appeared to be some fungi growing on older scales as my last picture shows.

This quick little study just confirms what many people had been telling me, that scale infestation doesn't help the quality of cut trees.

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