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© 2005 Plant Management Network.
Accepted for publication 13 September 2005. Published 16 September 2005.


Rhabdocline Needlecast Increases Needle Loss of Douglas-fir Christmas Trees


Ricky M. Bates, Assistant Professor, Department of Horticulture, The Pennsylvania State University, University Park 16802


Corresponding author: Ricky M. Bates. rmb30@psu.edu


Bates, R. M. 2005. Rhabdocline needlecast increases needle loss of Douglas-fir Christmas trees. Online. Plant Health Progress doi:10.1094/PHP-2005-0916-01-BR.


Rhabdocline needlecast caused by Rhabdocline pseudotsugae and R. weirii is the major disease affecting Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) production in Pennsylvania (2). Infected older needles normally are cast during summer, leaving severely infected trees with only one year’s complement of needles (Fig. 1). From fall through early spring, needles from the previous season develop chlorotic spots that are first yellow, and then later turn reddish brown (Fig. 2). Needles on infected trees harvested in the fall sometimes do not show symptoms, resulting in infected trees being sold to consumers and placed on display where they may develop symptoms. Tree freshness is of major concern to consumers and needle retention is a key component of postharvest Christmas tree quality (3). Little is known about the effect of Rhabdocline needlecast on needle retention characteristics of Douglas-fir. This report describes a needle retention comparison of healthy Douglas-fir branches with symptomless diseased branches.


     
 

Fig. 1. Rhabdocline needlecast infection results in the casting of older needles in late spring and summer, leaving severely infected Douglas-fir trees with only one year’s complement of needles.

 

Fig. 2. Early symptoms of Rhabdocline needlecast of Douglas-fir. Yellow spots develop on needles from October to January, before turning reddish brown.

 

During spring 2002, replicated field trials were conducted at a commercial Christmas tree farm in Clinton County, PA. Sheared Douglas-fir trees utilized were 6 to 8 ft tall and derived from a Lincoln National Forest seed source. Treatment and control trees were selected based on presence of uniform, heavy, natural infection and well-formed buds. Chlorothalonil (Bravo Weather Stik, Syngenta, Greensboro, NC) was applied four times at 1.30 g a.i./liter between May 1 and June 7, 2002 to twenty trees, and twenty trees were selected and left untreated. On November 5, 2002, four branches were removed from each fungicide-treated tree and from each symptomless nontreated control and transported to the post-harvest display room at Rock Springs, PA. Two branches from each group were placed in water and two were displayed dry for the duration of the four week display period. Needle loss data were obtained at days 0, 7, 14, 21, and 28 by randomly selecting 15 branches from treated and nontreated groups and gently rubbing two fingers over the needles. The extent of needle loss was evaluated on a 0 to 10 scale where 0 = none and 10 = 91 to 100% loss. On February 21, 2003, the site was revisited to verify that nontreated control trees were infected with Rhabdocline and that fungicide-treated trees were disease-free.

The presence of Rhabdocline needlecast had a significant effect on needle retention. Infected branches displayed dry had needle losses exceeding 20% after 14 days and over 30% after 28 days on display (Fig. 3). In contrast, healthy branches displayed dry exhibited less than 10% needle loss throughout the display period. Displaying infected branches in water reduced needle loss. Infected branches in water had significantly less loss after 14, 21, and 28 days compared to infected branches displayed dry and infected branches displayed wet never exceeded 15% needle loss. However, infected branches in water had a significantly higher rate of loss than healthy branches in water. Healthy branches displayed in water exhibited excellent needle retention with less than 5% loss after 28 days on display.


 

Fig. 3. Effect of Rhabdocline infection and display condition on current season needle retention of Douglas-fir branches. Needle loss was measured on a 0 to 10 scale where 0 = none, 10 = 91 to 100%. Bars represent SE of 15 replications.

 

Consumers demand Christmas trees that exhibit excellent needle retention characteristics. Needle drop has been identified as a major reason for not purchasing a live tree (1). In this trial, Rhabdocline-infected Douglas-fir trees had needle loss rates higher than healthy trees or infected trees kept hydrated. Many Douglas-fir trees are harvested in November and may not show clear infection symptoms. Early symptoms of Rhabdocline needlecast may also be confused with Cooley aphid feeding injury (4). Trees harvested in the Northeast U.S. may be shipped to distant destinations, increasing the probability of dehydration and increasing the risk of unacceptable levels of needle loss prior to or during indoor display. Growers need to be diligent about scouting and identifying Rhabdocline needlecast infection in Douglas-fir fields prior to harvest. If infected trees have been harvested, maintaining a high level of hydration can mitigate some of the adverse effects of Rhabdocline needlecast on needle retention. Controlling Rhabdocline needlecast during the year of harvest is a critical step in maintaining the postharvest quality of Douglas-fir Christmas trees.


Literature Cited

1. Helmsing, P. 2003. Consumers speak up: 2002 Wirthlin study. Am. Christmas Tree J. 47:30-33.

2. Merrill, W., and Cameron, E. A. 1986. Christmas tree pests and pest management in the Northeast. Penn. Agric. Sta. Prog. Rep. 388.

3. Seiler, J. R., Nichols, T. J., and Paganelli, D. J. 1988. Rehydration characteristics of cut white pine and Norway spruce Christmas trees. HortScience 23:164-166.

4. Walton, G. S. 1984. Rhabdocline needlecast of Douglas-fir. Am. Christmas Tree J. 28:35.