Pine Stem Rust Management Guidebook
Table of Contents
Management of white pine blister rust
White pine blister rust management process
This section outlines the methods for assessing the viability of white pine management. White pine blister rust greatly reduces the probability of white pine reaching maturity throughout the range of the species. Landscape level hazard and risk rating for white pine blister rust is quite simple. If white pine is present, it is at high risk from blister rust. The most important step in white pine management is the decision whether or not to manage for the species at all. The decision to manage for white pine involves a commitment to actively treat white pine blister rust.
In order for western white pine to be considered a potential crop tree, pruning is required as a part of the basic silviculture obligation. Proactive pruning treatments to control white pine blister rust have been effective at increasing the survival rate of young western white pine. One compelling use for white pine is to reforest laminated root disease infection centres on good growing sites where inoculum removal is not performed and species options are limited.
Research into developing rust resistant white pine is ongoing and the Ministry's commitment to a research strategy is outlined in the following policy statement (SIL 010; 90-02-16).
Current white pine blister rust incidence, as well as other forest health factors, should be assessed during the silviculture prescription walkthrough. Mature western white pine trees are often rust free since they were past the most susceptible phase at the time the rust was introduced into this province. The fact that these trees are rust free should not be interpreted as an indication of low blister rust hazard. Very few western white pine trees have exhibited genetic resistance to white pine blister rust. All areas of the province are considered high hazard for the purpose of prescribing white pine for regeneration purposes.
Stand management prescription
The proportion of western white pine and the incidence of blister rust in the stand should be assessed during a walkthrough. If the majority of the white pine have lethal blister rust infections (stem infections or branch infections <15 cm from the stem), management is not viable. If the white pine component of the stand is small and the majority of those trees are rust free, those stems may be pruned during a brushing or spacing treatment. If the white pine component is more substantial, and it is required to meet minimum stocking levels, a two lift pruning treatment should be considered.
Disease assessment and evaluation
Due to the nature of the host pathogen relationship it can be assumed that all western white pine are at high risk of infection unless pruning treatments are conducted. The decision of whether or not to manage for white pine depends in part on the results of the pre-stand tending survey.
Surveys for white pine blister rust
This type of survey may be done independently (i.e., if pruning is the only stand treatment planned) or may be conducted as part of a silviculture survey or pre-stand tending survey. The following sampling methods are suggested for use:
- Plots: sample all white pine within standard silviculture survey or pre-stand tending survey plots. Pw density is determined by:
- (Total number of Pw tallied) X (plot multiplier) / (number of plots)
- Strips: establish a series of sampling lines through the strata; sample all white pine within a predetermined distance on each side of a line. White pine density is then determined by:
- (Total number of Pw tallied) / [(strip area (ha) X (number of strips)]
Note: Express strip area as follows: [length (m) X width (m)] / 10000 m²
- Combination of the above two surveys (i.e., strips between plots).
Consider the following when designing a sampling scheme for white pine:
- Minimum sample size is 50 live trees.
- Tally Pw by the following infection classes: uninfected, non-lethally infected, and lethally infected.
- Schedule the survey for mid-May to mid-June when cankers and spores are highly visible (snow-free season is acceptable).
Assessment results will determine:
- rust incidence (infection level)
- suitability of white pine as a potential crop species if branch-pruned
- stems/ha of healthy or "prunable" white pine
- mean and maximum prunable height.
With the high variability in distribution of naturally regenerated western white pine, it is important in branch pruning projects to stratify openings based on white pine stocking or blister rust incidence.
Treatment methods for white pine blister rust
Branch pruning is a method involving the removal of all lower branches of uninfected and non-lethally infected trees. Branch infections that are >15 cm from the bole are termed "non-lethal" and, as such, are treatable. This is because, if the leading edge of the advancing canker is farther than 15 cm from the bole, the branch may be pruned without risk of the fungus having reached the bole. Branch pruning ensures that the infection will not reach the main stem and cause mortality. Lethally infected trees should not be branch pruned, rather they should be felled.
Proactive branch pruning for white pine has been shown to be an effective tool for preventing infection by white pine blister rust. Initial infection by white pine blister rust occurs on the current year's needles. Removal of all lower branches eliminates the infection court and any existing branch infections. A successful branch pruning for white pine blister rust usually requires two lifts. Detailed guidelines for pruning white pine are provided in Appendix 3. Refer to the Pruning Guidebook for proper branch pruning techniques.
Use of resistant seed
Use of registered, white pine blister rust-"resistant" seed is still largely experimental. If such seed is used, the requirement for mandatory pruning may be waived. However, the prescription should state that the stand must be assessed at free growing or when the trees are tall enough to undergo what would normally be the first pruning lift, whichever comes first. At that time, if stocking is still above target level, pruning may continue to be waived. If rust-caused mortality has caused stocking to fall below target level, then pruning must be conducted as soon as possible. Consult your regional pathologist before implementing this treatment.
Canker excising involves removing the live bark and cambial tissue 5 cm past the leading side edge of a stem canker, or base of a branch with a lethal canker, and 20 cm past the bottom and top edge of the visible canker margin. This is a time consuming process and should be limited to special, high value trees or unusual circumstances (e.g., saving trees in parks, recreation sites). All live tissue should be removed completely from within the scribed area as a narrow band of excised tissue may heal and be bridged by the fungus.
Free growing guidelines
Free growing damage standards
The following table specifies the criteria used for assessing individual trees in a free growing survey. The basis for unacceptability is the certainty that the types of damage listed below will result in mortality of potential crop trees. As a result, these damage standards are also applicable to stand management prescriptions included as part of incremental silviculture activities. They may also be used in pre-stand tending surveys and as decision criteria for crop tree selection during stand management treatments.
Table 4. Free growing damage standards for pine stem rusts in British Columbia
Free growing criteria and assessment
With respect to stands infected with pine stem rusts and the associated treatment of infected strata, the following procedures define the criteria for assessing and determining if the free growing obligation has been met.
Assessment of strata treated under a silviculture prescription
Treatment of pine stem rusts should be integrated into silviculture prescriptions on all sites where pine is at risk, irrespective of site hazard. The minimum treatment on all sites referred to in this guidebook is the careful assessment of the infection level on all sites combined with the eradication of lethally infected stems during stand tending activities such as spacing and pruning. The primary goal of this treatment is the protection of the established stand and stand tending investment.
If a stratum has been thinned and the presence of pine stem rusts results in the non-achievement of a free growing stand, then the approved free growing obligations, and any costs associated with achieving these obligations, will remain the responsibility of the licensee.
The prescription writer must be certain that free growing status is achievable before prescribing stand management treatments. All young pine stands must be assessed using the accepted free growing damage criteria regardless of the type of treatment prescribed. Failure to reach free growing due to pine stem rusts will be the responsibility of the licensee in all cases.