WSU Christmas Tree Research Newsletter

Joe Hudak,
Ag Research Techonogist
Washington State University,
Puyallup Research and Extension Center
7612 Pioneer Way East
Puyallup, WA 98371-4998
253-445-4596
e-mail: hudak@wsu.edu

Thank You
A special thank you to the 113 growers and businesses who voluntarily gave $59,000 to Washington State University through their contributions to the PNWCTA Advanced Research Program. Individual contributions ranged from $5 to $10,000. These were received from Washington, Oregon, California, Texas, Maine, and British Columbia. The success of this program is largely due to the efforts of the Advanced Research Program committee, and its chair Ken Scholz. These funds are being used to support Joe Hudak and a portion of Kathy Riley's time. They are critical to WSU's efforts to address the disease, entomology, and keepability issues that are important to the Christmas tree industry.

Comings and Goings
Dr. Then Thomsen, a Fulbright scholar from the Danish Forest and Landscape Research Institute, completed her sabbatical working in Gary Chastagner's lab. While here, Iben worked on bud abortion problems in true firs and helped with Chastagner's Annosus root rot project. She also participated in several industry meetings and had the opportunity to learn more about the Christmas tree industry in the PNW.

Mattias Pettersson, a Ph.D. student at the Southern Swedish Forest Research Center in Alnarp, Sweden also spent about 7 weeks working in Gary Chastagner's lab this past spring. Mattias has been studying various aspects of the cultural management of Annosus root rot in Swedish forests. He assisted in our efforts to better understand the root-to-root spread of Annosus root rot in noble fir Christmas tree plantations.

Update on Annosus Research
During 2001, 19 field plots were established to obtain a better understanding of the extent of mortality that can result from Annosus root rot. About 31,000 trees planted between 1997 and 2000 were examined for aboveground symptoms such as branch flagging, wilting, and death. Symptomatic trees in these plots ranged from 0.3% to 13.6%. If missing and replanted trees were included, the maximum rate reached 29.9%. Annosus root rot was associated with 87.8% of the dead and dying trees in these plantations and was detected on noble, Fraser, Nordmann, and Grand fir, as well as on Douglas-fir. Noble and Fraser fir appear to be very susceptible to this disease. During this past spring and summer, additional trees have been killed in many of these plantations. We have almost completed additional examination of the trees in these fields to determine the extent of symptom development that occurred during the past year.

Disease spread
Annosus root rot is caused by the fungus, Heterobasidion (Fomes) annosum. It spreads via two methods. Initial infections in Christmas tree plantations probably occur when fruiting bodies on diseased trees and stumps in nearby forests release airborne spores that colonize freshly cut stumps or wounds on trees in plantations. In forest studies spore dispersal occurs throughout the growing season, but dispersal is greatest in the fall, which coincides with when Christmas trees are harvested. Once the disease becomes established in a Christmas tree plantation, fruiting structures can be produced on trees or stumps and once again spread the disease to nearby freshly cut stumps during harvest. After the spores land on freshly cut stumps, which are susceptible to infection for only a short period of time, they germinate and begin to colonize it. The fungus spreads to the stump's roots and then into the roots of adjacent healthy trees that contact the colonized roots. Seedlings also can become infected when their roots come in contact with diseased roots and stumps left from the previous crop. Unlike some needle cast diseases that can build up quite rapidly, the buildup of Annosus in plantations takes place over a period of years.

Harvest is an excellent time to check whether Annosus root rot is present in your fields. After cutting the tree, look for staining of the stump. If the stump and roots are dug, Annosus-infected trees may also have cream to buff-colored fruiting structures on the stump near the soil surface or on infected roots. Initially, it may help to send samples to a plant clinic for identification. Management of this disease in forest situations is based on limiting spore infection of freshly cut stumps and the root-to-root spread of the pathogen. Limited information is available regarding the effectiveness of these practices in controlling this disease in Christmas tree plantations.

Stump Treatments
Stump treatments often are recommended to protect freshly cut stumps from infection by spores in forest situations and they are likely to be beneficial in Christmas tree plantations. At this time, the only registered stump treatment available in Washington and Oregon is a borax product, "Sporax", marketed by Wilbur Ellis. This product is applied to freshly cut stumps to prevent them from becoming infected by the fungus spores. Last year we conducted one field trial and two trials using cut sections of stumps to determine the effectiveness of Sporax, urea, soil, and several fungicide products in protecting freshly cut stumps from spore infection. Because of problems associated with root-to-root spread of the disease in our field trial, the only results we have at this time are from the two trials using cut sections of stumps. Data from these trials indicate covering the stump surface with Sporax was the only treatment that consistently protected stumps from infection. Spraying the stump surface with a 20% urea mixture or covering the stump with soil right after cutting appeared to be effective in one trial, but not in another. Although additional work is needed to confirm these studies under field conditions, the Sporax treatment appeared to be the best treatment for protecting freshly cut stumps from infection.

Treatments should help protect stumps from spores from nearby infected forests and Christmas tree fields as well as spores produced on diseased trees that are already present within fields. Apply Sporax to the stump as soon as possible after cutting the tree, preferably within a couple of hours. If you apply Sporax later than this, the fungus already may have infected the stump. Sporax is a granular material, which should be applied using a container having a shaker top, such as a jar with nail holes punched in the lid. In the case of choose-and-cut fields, it may be helpful to also spray the surface of the stump with dye to identify stumps that have already been treated.

Stump Removal
One of the most effective cultural methods of controlling Annosus root rot in forest settings is the removal of stumps and roots prior to replanting. The effectiveness of this method depends on the size of the residual pieces of stumps and roots prior to replanting. The effectiveness of this method depends on the size of the residual pieces of stumps and roots left in the field. The fungus that causes Annosus root rot does not compete well against other microorganisms present in the soil. Thus, its potential to cause disease in a new planting depends on the size of the pieces of infected roots and stumps, the susceptibility of the newly planted trees, and the time it takes for the seedling's roots to come in contact with infected roots and stumps. Trials are currently underway to examine the effectiveness of some of the various types of stump and root extraction or grinding equipment that are currently available in removing stump and root material from Christmas tree fields. The use of a fallow period or various cover crops following stump removal may also limit the amount of inoculum present at the time of replanting.

One important question is how many diseased trees can be present in a field before a grower needs to think about removing all stumps and large roots prior to replanting. If a grower plants a susceptible species next to a diseased stump, it is likely this tree will be killed prior to harvest. What is unknown at this point is how many of the nine replanted trees surrounding the diseased stump will be killed prior to harvest. In some cases it might be all of them. This would mean that for every diseased stump a grower sees in the field, expected loss could range from 1 to 10 of the trees replanted around each stump. If many diseased stumps remain in the field at the time of harvest, growers need to remove them and as many of the roots as possible prior to replanting to minimize future losses.

In our 2001 study of five fields where no Annosus root rot was found, three fields had had the stumps and larger roots from the previous rotation removed prior to planting Noble, Fraser, and Grand fir seedlings. While it is not realistic to expect that stump removal will eliminate Annosus root rot, it likely will reduce the extent of losses from this disease. Stump removal may also have some additional benefits such as reducing soil compaction, which improves the growth of replanted trees. Where it is not practical to remove stumps, it may be possible to limit disease spread by digging a 2-3' deep trench to isolate infected trees. This would prevent the roots of the healthy trees from coming in contact with those of the diseased trees.

Additional information relating to the WSU Puyallup Christmas tree research program and our Annosus research project is contained in the two Lookout articles listed below.

Publications:
Chastagner, G. A. 2002. PNWCTA advanced research update. Christmas Tree Lookout 35(2): 26-30. Chastagner, G. A. 2002. Annosus root rot – An emerging problem for Northwest Christmas tree growers. Christmas Tree Lookout 35(3): 10-15.

Workshop:
On October 2nd and 3rd, we are hosting a two-day workshop dealing with the recognition and management of insect, disease, and weed problems in Christmas tree plantations. This workshop will be held at WSU Puyallup. In addition to offering hands on materials to work with, part of the workshop will involve visits to Christmas tree research plots. Registration is limited to 40 growers. We plan to hold one of these workshops per year. If you are interested in future workshops, contact WSU Pesticide Education Coordinator Carrie Foss (253) 445-4577.

Presentations:
Gary Chastagner and Joe Hudak gave a research update at the PNWCTA Annual Summer meeting and
organized a field tour stop relating to Annosus root rot.

Gary Chastagner made two presentations, "Managing True Fir Root Rots" and "Christmas Tree Freshness – Making it a Priority", at the recent National Christmas Tree Association Conference in Michigan.