When managing root disease in young stands, several strategies may be considered. Each strategy has its own set of characteristics which makes it suitable for use under certain circumstances. Brief overviews of the four major strategies for root disease are given as well as procedures for suggested tactics. When considering a strategy, use Table 8 to weigh the relative advantages of each and their associated tactics or methods of application given your particular circumstances.
Thinning, or other stand management treatments, on any root disease infected site should be carefully reviewed before any stand management prescription is submitted or approved.
Table 8. Stand management prescription strategies and tactics
This strategy attempts to lower the probability of contact with root disease by removing infected material from the soil. For Armillaria, thinning an infected site can greatly enhance the spread of root disease, and subsequent mortality, by increasing the fungal food base and allowing unhindered spread through young root systems.
Pop-up spacing is a method which simultaneously removes root inoculum from the soil while conducting stand management operations. This method uses a small feller buncher or excavator to “pop-up” infected trees and roots out of the ground. This method is undergoing operational trials in Armillaria-infested stands in the interior.
This tactic involves pulling saplings from the ground, roots and all, to prevent the spread of root disease (particularly Armillaria). By the time root contacts re-establish, the saplings may be large and vigorous enough to resist infection. Pop-up spacing is conducted using rules similar to those for conventional spacing. For example, the priority of crop tree selection for pop-up treatment is: health first; species second; and density third. The general rule is “when in doubt, pull it out.”
Field operators must clearly understand that this activity is an important stand entry for maintaining stand health, and one that may damage residual trees and cause some site disturbance. The operator must read and understand the stand management prescription. The operator should:
In order to accomplish these tasks effectively, the operator must:
This strategy is recommended to check the spread of root disease when disease levels are minimal or when specific infection centres can be delineated in a stand. When spacing, favour species which do not suffer mortality or growth loss from the root disease on site. Where possible, immune or tolerant species should be left as a buffer surrounding each infected tree or centre.
Site productivity and other desired objectives may be compromised when favouring a more resistant species. Favouring broadleaf species rather than conifers is often the only choice in areas with high levels of root disease and limited alternate species. This tactic can provide additional benefits in satisfying wildlife values and biodiversity issues, while still providing significant forest cover and supply of fibre.
This tactic favours retaining less susceptible tree species within 5 m of any infected tree or infection centre during precommercial thinning. All infected trees should be removed, but when infected trees are left, they should not be within 5 m of any other currently uninfected but susceptible tree. This procedure is not recommended for use when root disease exceeds alternate levels in a stand.
Consult Table 1 to determine which tree species to favour when thinning root diseased stands.
This strategy relies on lowering the probability of young tree roots contacting inoculum from residual stumps or roots left after spacing. This entails establishing a lower conifer density than desired in order to reduce the chance of root contact occurring between infected and uninfected trees. This strategy may be difficult to implement in most stand management situations.
This tactic is based on the concept of creating dysfunctional “bridge-tree” root systems between infected and uninfected stems in a stand. This impedes fungal pathways for tree-to-tree spread of disease. Dysfunction of the root system occurs because of colonization by other antagonistic organisms.
This procedure is currently recommended only for Phellinus in coastal forests. This tactic will not be effective against Armillaria especially in the interior. Be certain of root disease conditions in your stand before applying this method. This method should also work with Tomentosus. Consult your local forest health specialist before attempting.
Species to be marked for removal within Phellinus centres are Douglas-fir, amabilis and grand fir. Within centres retain western redcedar, western hemlock, lodgepole and western white pine, and all broadleaf species.
Figure 11. Sample diagram of bridge tree removal.
The strategy of employing chemicals to treat root pathogens has a long history. Products such as Borax are well known surface sterilants and have been used in the past to reduce the chance of Annosus invading freshly cut stump surfaces following spacing. Unfortunately, the efficacy of this treatment is too variable to endorse its use. Currently, no chemicals are advocated for use with stand management treatments.
The use of biological agents to treat root disease is a relatively recent development. Many naturally occurring fungi have recently been found which are direct competitors of several common root pathogens. Currently, there are no biological agents advocated for use against root pathogens in B.C.