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Project description

The impacts of pitch canker on susceptible pines in California. (01XU031)
Program Exotic Pests and Diseases Research Program
Principal
investigators 		T.R. Gordon, Plant Pathology, UC Davis
D.L. Wood, Insect Biology, UC Berkeley
Host/habitat Monterey Pine; Pines
Pest Pitch Canker Fusarium circinatum
Discipline Plant Pathology
Review
panel 		Urban Systems
 Start year (duration)  2001 (Three Years)
Objectives Characterize the susceptibility of Monterey pines showing disease remission.

Document changes in tree susceptibility to pitch canker over time.

Prepare guidelines on removal of trees affected by pitch canker.

Final report The purpose of this project was to better characterize the impacts of pitch canker so that landowners could make more informed decisions about tree removal. To this end, we have characterized the susceptibility of trees in 16 different locations (plots): eight in areas where pitch canker was well established (old areas) and eight in areas where the disease was a more recent occurrence (new areas). In 2002, 20 trees in each plot were tested for susceptibility by making an artificial inoculation on each of three branches on each tree. The results showed that trees in areas where pitch canker is of long residence tend to be less susceptible to the disease than trees in areas where pitch canker has only recently become established. Similar results were obtained when the same trees were inoculated in 2004, but the magnitude of the difference between areas was less than in 2002. In a separate study, we gauged the susceptibilities of trees that were once severely diseased but were subsequently free of pitch canker (=disease remission). A total of 82 trees in seven plots were tested and nearly all were highly resistant to pitch canker. These results are indicative of induced resistance, something that has not previously been demonstrated in either hardwood or coniferous trees. Induced resistance appears to be a critical component of disease remission and can be expected to moderate the impact of pitch canker on susceptible pines throughout California. This information has been used to update the guidelines on tree replacement that were originally prepared and disseminated by the California Pitch Canker Task Force.

Third-year
progress 		The purpose of this project is to better characterize the impacts of pitch canker so that landowners can make more informed decisions about tree removal. To this end, we have characterized the susceptibility of trees in 16 different locations (plots). Eight plots are located in areas where pitch canker is well established, and the remaining eight are in areas where the disease is a more recent occurrence. Twenty trees in each plot were tested for susceptibility by making an artificial inoculation on three branches of each tree. The inoculated branches were removed and rated for the extent of pathogen development, based on the length of the discolored area beneath the bark, twenty weeks later. The results show that trees in areas where pitch canker is of long residence tend to be less susceptible to the disease than trees in areas where pitch canker has only recently become established. This difference is consistent with our expectations that exposure to the pathogen leads to enhanced resistance in the host. Further confirmation of this trend will be sought by monitoring the susceptibility of the tested trees over time. In a separate study, we are determining the susceptibilities of trees that were once severely diseased but now have no symptoms of pitch canker. These trees demonstrate the phenomenon of disease remission. It is our hypothesis that these trees have gone into remission because they are now more resistant to pitch canker. To determine if this is the case, we are testing trees at seven different locations where we have been monitoring the disease status of trees since 1992. At the conclusion of our study, we will use the information obtained to update the guidelines on tree replacement, which were originally prepared and disseminated by the California Pitch Canker Task Force.

Second-year
progress 		Since the inception of this project, we have worked with 18 different land owners in order to locate sites suitable for our studies. We have now established the 16 plots needed to test for differences in susceptibility between old and new sites, and to monitor changes in susceptibility over time. Twenty trees in each plot were tested for susceptibility by making an artificial inoculation on each of three branches on each tree. After allowing the pathogen to develop for a period of approximately 20 weeks, all the inoculated branches were removed and rated for the extent of pathogen development, based on the length of the discolored area beneath the bark. The results show that trees in areas where pitch canker is of long residence tend to be less susceptible to the disease than trees in areas where pitch canker has only recently become established. This difference is consistent with our expectations that exposure to the pathogen leads to enhanced resistance in the host. Further confirmation of this trend will be sought by monitoring the susceptibility of the tested trees over time. At the conclusion of our study, we will use the information obtained to update the guidelines on tree replacement, which were originally prepared and disseminated by the California Pitch Canker Task Force.

First-year
progress 		During the first year of this project our objective was to establish long-term monitoring plots that would allow us to document changes in the susceptibility of Monterey pine to pitch canker, an important disease affecting pines in California. The first step in this process was to identify suitable sites for the study. To this end we have surveyed prospective sites in Monterey and Santa Cruz Counties and identified 19 stands of Monterey pine that satisfied the following criteria: 1) the general area in which the stand occurred was already infested with pitch canker, 2) pitch canker was present or absent within the stand but some trees remained uninfected, and 3) a minimum of 40 trees in the stand had branches that were accessible from the ground. The second step is to gain permission from the landowners to conduct the study using trees on their property. This is a time consuming process because 14 different landowners are involved. As of this writing we have received permission from five landowners, who collectively account for seven of the nineteen candidate sites. Three other sites are in California State Parks. We have submitted a permit application to cover these three sites and we anticipate approval of our application in the near future. That will provide us with ten of the required 16 sites. Three additional landowners are receptive to our proposal but have requested additional information concerning the study, which we have provided. We are in the process of establishing contacts with other landowners in order to secure the necessary permissions for three additional sites. While the process of gaining landowner approvals continues, we will initiate testing of trees in the plots where we have permission to conduct our studies. We hope to have half the plots established by the end of May. At the conclusion of the study we will have better information on the extent to which pitch canker damages Monterey pines. This information will be used to refine guidelines for the retention and removal of trees in areas where pitch canker is a problem.

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