Author(s): Dennis W. Fulbright, Sara Stadt, Mursel Catal, and Janette L. Jacobs, MSU Department of Plant Pathology
Where Published: Nursery, Landscape and Christmas Tree Research Projects and Educational Programs
Date of Publication: December 2003
Research Dates: 2000-2003
Subject Area: Phytophthora root rot in Abies fraseri

Summary: The purpose of this study was to survey Michigan Christmas Tree plantations and nurseries for root rot and identify the species of Phytophthora associated with diseased Fraser fir. This knowledge will allow us to institute management plans for Phytophthora root rot in Michigan Christmas Tree plantations and to identify fir species resistant to Phytophthora root rot.

Results
Similar to results of a survey conducted in 1986, the most common species of Phytophthora found associated with Fraser fir plantings in Michigan were P. citricola and P. cactorum. Although P. cinnamomi is highly pathogenic to Fraser fir and is problematic in North Carolina, it was not recovered in Michigan in this or the 1986 survey. It has been suggested that P. cinnamomi is poorly adapted to the cooler temperatures of Michigan soils.

Of significance, however, was the finding of another species that has been difficult to characterize. Different aspects of this strain resemble both P. megasperma and P. cryptogea. Other P. megasperma isolates have not been able to cause disease on Fraser fir, but this novel strain is strongly pathogenic to Fraser fir and appears to be new to Michigan farms.

Other species of Phytophthora including P. medicaginis, P. europa, P. gonapodyides and P. nicotianae were also found associated with the roots of dying Fraser fir, but their role in disease, if any, is not well understood.

Using the most pathogenic Phytophthora species from our recent survey, we inoculated various fir species in greenhouse tests. In these assays, it appears that Canaan and balsam fir were more tolerant of root rot than Fraser fir.

A unique opportunity to test the results of our greenhouse studies on root rot resistance in Canaan fir appeared during our survey. Both highly pathogenic and weakly pathogenic isolates of Phytophthora were present in the soil where a severe root rot epidemic was occurring. It was obvious at the outset that the root rot was associated with contaminated nursery stock from an out-of-state nursery since diseased trees abruptly stopped in the eighth row of a 14-row landing where nursery stock from one nursery was changed to that of another.

The next six row of Fraser fir were from an in-state nursery and no trees in these six rows showed symptoms of root rot. Furthermore, not only did the Fraser fir in this field originate from different nurseries, but the Fraser fir landings at one point were separated by a landing (16 rows) of Canaan fir. Similar to our greenhouse results, the Canaan fir did not develop root rot even though water drained from the diseased trees directly through the Canaan fir landing.

Another landing of Fraser fir planted to the far side of the Canaan fir began to develop Phythophthora root rot later in the study. This disease pattern strongly supports the probability that Phytophthora spores were carried by the drainage water through the Canaan fir planting to the Fraser fir landing on the far side. Yet, the passage of Phytophthora spores through the Canaan fir did not lead to any root rot of the Canaan fir, suggesting some level of field tolerance in Canaan fir.

These observations supported our greenhouse inoculation assays that suggested higher levels of resistance to Phytophthora root rot could be found with Canaan fir as with Fraser fir. Second, it may be possible to graft Fraser fir to fir root stock with high levels of root rot resistance. This at first would appear to be prohibitively expensive. But, using these grafted trees to expand fir acreage into areas where root rot would normally be expected to infect trees could increase premium fir production acreage in Michigan.

To obtain copies of this report, contact:
Jill O'Donnell
Michigan State University Extension Service
School of Natural Resources
401 N. Lake Street, Suite 400
Cadillac, MI 49601
Phone: 231/779-9480
E-mail: odonne10@msu.edu

Author(s): Robert J. Richardson & Bernard H. Zandstra
Where Published: Nursery, Landscape and Christmas Tree Research Projects and Educational Programs
Date of Publication: December 2003
Research Dates: Spring 2003
Subject Area: Weed control

Summary:
Significance
Hoary alyssum is an invasive biennial mustard that may form dense stands in Christmas Tree plantations. This weed produces numerous small, white flowers and many seeds. Hoary alyssum competes with trees for nutrients and is very difficult to control.

Materials and Methods
A study was conducted in spring 2003 near Hart, Mich., to evaluate hoary alyssum control with various herbicides. Treatments were applied as a direct spray to Fraser fir Christmas Trees with established populations of hoary alyssum on April 24, 2003.

Weed control and crop injury was visually rated on a 0 to 100% scale with 0 equal to no weed control or no crop injury and 100 equal to complete weed or crop death. Sprayer output was 20 GPA. An untreated control was included for comparison to herbicide treatments.

Results
Fraser fir injury from herbicide treatments was less than 5% with all treatments. Hoary alyssum control on June 18 was at least 77% with all treatments except Stinger plus Cobra. Control with this treatment decreased to 37% at later ratings.

On July 17, control was 53 to 63% with Permit, Cobra, and SureGuard plus Roundup Original. Control was 73 to 74% with Roundup Original alone and Princep plus Goal 2XL. Hoary alyssum control was greatest with Garlon at 98% on July 17 and 87% on September 5. Other treatments controlled hoary alyssum 23 to 63% on September 5.

Conclusions and Future Research
Season-long control of hoary alyssum was only observed with use of Garlon. Other treatments provided initial suppression of the weed, but hoary alyssum recovered and was able to produce flowers and seed. However, SureGuard and Princep plus Goal 2XL treatments did reduce the amount of new hoary alyssum plants emerging during the summer as compared to other treatments.

While the majority of these treatments did not control the weed adequately, fall applications of the same herbicides might produce better results. Hoary alyssum plants would be smaller in the fall than in spring and may be more sensitive to treatment then. This research will be repeated in spring 2004 and a similar study will be established in fall 2003.

To obtain copies of this report, contact:
Jill O'Donnell
Michigan State University Extension Service
401 N. Lake Street, Suite 400
Cadillac, MI 49601
Phone: 231/779-9480
E-mail: odonne10@msu.edu

Author(s): Gary Chastagner, Kathy Riley, Everett Hansen and Wendy Sutton
Where Published: Christmas Tree Lookout Date of Publication: Winter 2004
Research Dates: 2003
Subject Area: Determine susceptibility of conifer shoots to infection by sudden oak death (Phytophthora ramorum) and screening of fungicides for controlling SOD.

Summary:
Methods
Inoculation studies were conducted for 25 conifer species in 2003. Tests with coastal Douglas-fir indicated that infection generally occurs shortly following bud break and that new growth is susceptible for only a few weeks in natural conditions.

Results
Only 5 species were not susceptible (Dawn redwood, Austrian pine, eastern white pine, Himalayan blue pine, ponderosa pine). The susceptible species included most grown for Christmas tree production. However, it is unclear whether they woudl become infected under field, rather than test, conditions.

Fungicide tests indicated that several have the potential to provide excellent control on Douglas-fir. Additional tests are being conducted to confirm the effectiveness of fungicides on some highly susceptible true firs and to determine their residual activity.

To obtain copies of this report, contact:
Gary Chastagner
Western Washington Research and Extension Center
7612 Pioneer Way East
Puyallup, WA 98390
Phone: 253/445-4528
E-mail: chastag@wsu.edu

Author(s): Gary Chastagner
Where Published: Christmas Tree Lookout Date of Publication: Winter 2004
Research Dates: 2001-2003
Subject Area: Can Annosus root rot, which is spread by root to root contact, be reduced by removing stumps before replanting an infected field?

Summary:
Methods
21 tree fields in Washington and Oregon were monitored for three years and losses due to Annosus were recorded. Three fields had roots removed from sections before replanting so a comparison where roots were left intact was possible.

Results
The highest mortality in a field with roots was 40%. The highest where roots were removed was 14%. Removal of stumps significantly reduced mortality between 74% and 94%, but did not eliminate it.

Since these three fields were replanted the spring following harvest and stump removal, it is unknown what effect planting a cover crop and waiting one year would have on disease development. It is also unclear how effective other methods of removal, such as grinding, would have.

To obtain copies of this report, contact:
Gary Chastagner
Western Washington Research and Extension Center
7612 Pioneer Way East
Puyallup, WA 98390
Phone: 253/445-4528
E-mail: chastag@wsu.edu