Concolor needle drop
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Recently, MSU Extension statewide Christmas tree Educator Jill O’Donnell and I visited a Christmas tree grower and landscape nursery on the west side of the state. The grower was having a significant issue with needle drop in Concolor fir. Some trees that were dug only a few days prior to our visit had dropped almost all their needles. The problem was occurring on trees of varying sizes and that had been dug from different fields. Moreover, the grower reported they had issues with needle drop in some Concolor firs that were cut last year for Christmas trees. Examination of needles by MSU Diagnostic Services did not indicate any needle-cast pathogens were present.
What’s going on?
For the landscape trees, there appears to be a couple of factors at work. Dr. Rick Bates, a professor at Penn State Department of Horticulture, has extensive experience with Concolor and notes that this species frequently has needle retention issues, especially if trees don’t receive enough cold weather in the fall to firmly set needles. In addition, Concolor firs tend to have coarse root systems compared to many other conifers, so they tend to lose a lot of root area when dug. This means trees can dry quickly after harvest. In the nursery we visited, trees that were dropping needles had relative water content of less than 50 percent, while trees which held their needles had needle relative water content over 100 percent.
What to do?
The key thing is for growers to do everything possible to preserve root area (such as oversizing root-balls), keep roots moist (water trees before digging and keep balls moist), and reduce water loss (keep trees shaded during storage and handling).
Dr. Bates adds that even though Concolor firs may drop all their needles, buds are unaffected and trees often survive transplanting. The challenge for a grower, of course, is convincing a customer that a tree that just dropped all its needles is really OK.
