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Gary A. Chastagner and Kathleen L. Riley

Moisture and needle loss characteristics were similar for noble (Abies procera Red.) and Nordmann fir [Abies nordmanniana (Stev.) Spach.] Christmas trees that were displayed in water. After 42 days, trees still had xylem pressure potentials above -2 MPa. In addition, trees that were displayed in water had very little needle loss. When trees were displayed dry, noble and Nordmann fir had similar rates of moisture loss, drying to about -6 MPa in about 3 weeks. Although there was very little needle loss from any of the noble fir trees that were displayed dry, some Nordmann fir trees began to shed large numbers of green needles within 3 to 5 days, which significantly reduced postharvest quality. Unless sources of Nordmann fir are identified that have good needle retention characteristics, the needle loss problem observed when trees dry to about -3 MPa has the potential to limit the use of this species as a Christmas tree in the United States.

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Ulrik Bräuner Nielsen and Gary A. Chastagner

Needle retention is an important trait when selecting for high quality Christmas trees. Nordmann fir [Abies nordmanniana (Stev.) Spach.] is generally considered to have good needle retention, but recent research has shown that when cut trees are allowed to dry, significant needle loss problems can develop. This has the potential to limit the use of this species in situations where trees are harvested early, shipped long distances, sold in warm weather markets and displayed for extended periods of time. A set of 39 provenances where tested to identify provenance differences in needle retention. Branches where collected in two consecutive years in October in 1999 and 2000 and November 2000. Small branch samples where cut and displayed indoors under controlled conditions and allowed to dry. Strong provenance differences in needle loss were seen for all three test dates. No significant interactions were seen among the October collections, but significant rank changes occurred from October to November. Predicted (BLUP) provenance mean values ranged between 11% and 27% for needle loss when branches where allowed to dry, averaging all three tests. Despite only one test location, the study clearly indicates that it should be possible to select for provenances with generally better needle retention characteristics.

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Gary Chastagner, L. Eric Hinesley and Jeff Owen

SafeTree Christmas Tree Fire Retardant was applied to freshly harvested Douglas fir [Pseudotsuga menziesii (Mirb.) Franco] boughs, and RapidCool FRX Christmas Tree Retardant was applied to freshly cut Fraser fir [Abies fraseri (Pursh) Poir.] boughs. The flame retardants were sprayed onto the foliage. Fire retardant accelerated the drying rate of Douglas fir boughs, which increased flammability. RapidCool fire retardant did not slow the drying rate of Fraser fir boughs, and had no effect on moisture content (MC) at ignition, flame time, total burn time, or total foliage consumed. For both species, initial ignition and spread of flame occurred at 60% to 70% MC. Fresh boughs did not ignite in burn tests and were not a fire hazard. Twig MC of nontreated Fraser fir increased 20% during display in water, further decreasing the possibility of ignition when exposed to a flame. Neither product was effective as a fire retardant on boughs of Christmas trees.

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Gary A Chastagner, Ulrik Bräuner Nielsen and Kathleen L. Riley

Postharvest moisture and needle retention of boughs was examined for four Danish and five U.S. provenances of noble fir grown in Denmark. Boughs were displayed indoors under controlled conditions, and data were collected relating to rates of moisture loss and needle retention. Small current-year shoots had moisture and needle loss patterns similar to larger bough material. Postharvest quality of the Danish and U.S. provenance boughs was very similar. There was also a high correlation between the moisture level of the boughs and shoots, indicating that it should be possible to use small shoots to assess differences in moisture retention in future tests.

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Rita L. Hummel, Marianne Elliott, Gary Chastagner, Robert E. Riley, Kathy Riley and Annie DeBauw

Growth and susceptibility of evergreen Rhododendron ‘English Roseum’, ‘Cunningham’s White’, and ‘Compact P.J.M.’ to Phytophthora ramorum in response to biweekly nitrogen (N) fertilizer application at rates of 25, 75, and 150 mg N per 11.4-L container was evaluated during two growing seasons. At the end of both growing seasons, horticultural evaluation of the different plants showed that 150 mg N-fertilized cultivars had superior shoot growth, visual quality, leaf color, and the highest leaf N concentration, whereas the 25-mg N cultivars were inferior for these characteristics. Plants fertilized with the 75-mg N rate were typically intermediate to the 150- and 25-mg N plants for the measured characteristics. During the first growing season, the number of flower buds on ‘Cunningham’s White’ and ‘English Roseum’ was not influenced by N rate but the second season bud numbers increased with increasing N fertilizer. Foliar susceptibility to P. ramorum was influenced by N fertilizer application rates in the most susceptible cultivars, ‘English Roseum’ and ‘Cunningham’s White’, in which lesion size and infection frequency both increased at higher N rates. The results were variable in ‘Compact P.J.M.’, the most resistant cultivar.