[
Root Disease Management Guidebook Table of Contents]

Treatment methods

Strategies and tactics for silviculture prescriptions

When managing root disease in a stand scheduled for harvest, 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 6 to weigh the relative advantages of each and their associated tactics or methods of application given your particular circumstances.

Partial cut harvesting or commercial thinning of any root disease infected site should be carefully reviewed before any prescription is submitted or approved.

Table 6. Silviculture prescription strategies and tactics

Strategy and tactics: inoculum removal

Overview

This strategy attempts to lower the probability of root disease transmission by removing infected material from the soil. Stumps and large roots may harbour the viable inoculum of some pathogenic fungi for up to 35 years. Reforesting an infected site can perpetuate root disease and increase future mortality as trees become infected at an earlier age.

The recommended methods for removing the inoculum of all root diseases are stumping and push-over harvesting. Stumping removes stumps and large roots in a separate step following harvest while push-over harvesting simultaneously incorporates stump and root removal into the falling operation. Both of these methods work well at reducing inoculum loads. There are some constraints arising from the use of heavy machinery, which may increase the risk of excessive soil disturbance on some sites. Use of a skilled equipment operator can substantially reduce this risk. Table 7 outlines some criteria for evaluating mechanical inoculum removal. Site sensitivity assessment procedures are central to evaluating mechanical inoculum removal options.[1]

Table 7. Site characteristics and constraints checklist for mechanical treatment

Procedure stumping

Overview

Stumping is a well tested and effective method for removing stump and root inoculum from a site.

Pros:

Cons:

Field procedure

  1. After a survey has been conducted, stratify the treatment areas for stump removal.

  2. Evaluate terrain and soil sensitivity prior to, and after logging, to determine sensitivity of site to potentially detrimental soil disturbance (see Table 7).

  3. Prescribe treatment in silvicultural prescription.

  4. Use proper equipment and techniques to minimize soil disturbance, such as lifting and rolling stumps rather than pushing them. Use of excavators with bucket and thumbclaw attachments is recommended. Use of bulldozers is not acceptable.

  5. Inspect and monitor operations continuously to avoid excessive site or soil disturbance. Operations should be postponed during heavy rain or snow.

Procedure push-over harvesting

Overview

Push-over harvesting is a method for removing infected stump and root inoculum from a site during harvest. This method has been tested for use on Armillaria, and is undergoing testing for use on sites with Phellinus and Tomentosus.

Pros:

Cons:

Refer to Table 7 for site characteristics and constraints checklist.

Strategy and tactics: alternate species selection

Overview

This strategy is the most frequently recommended to treat root disease, as it most closely mimics ecological processes. The alternate species strategy is most effective when implemented for minimal to alternate disease levels, or when specific strata can be targeted for regeneration to immune or less susceptible tree species.

The concept is simple; regenerate with species that suffer little to no mortality or growth loss from a specific root disease. Ecological host suitability, site productivity, and other desired objectives may be compromised when selecting an alternate species, depending on desired future stand conditions.

A prescription of broadleaved/conifer mixes rather than pure conifers generally will result in lower root disease levels and regeneration risk, and is often the only choice in areas with high levels of disease and few acceptable alternate conifer species. This tactic can provide additional benefits in satisfying wildlife values and biodiversity issues, while still providing significant forest cover and supply of fibre.

Procedure selecting less susceptible species

Overview

Consider several options for selecting less susceptible host species:

Pros:

Cons:

Consult Table 1 to determine which tree species to favour when regenerating root diseased stands.

Procedure hardwood cropping

Overview

This strategy uses immune species over a short rotation (up to 35 years) to reduce inoculum levels by not introducing new food sources for fungal colonization. This tactic is currently being tested as an operational treatment and is not yet recommended for widespread operational use. Consult your local forest health specialist before attempting this treatment.

Pros:

Cons:

Procedure conifer fallow

Overview

This strategy uses seeded grasses or legumes over a short (up to 35 years) period to reduce inoculum levels by not introducing new food sources for fungal colonization. This tactic is currently being tested as an operational treatment and is not yet recommended for widespread operational use. Consult your local forest health specialist before attempting this treatment.

Pros:

Cons:

Strategy: inoculum avoidance

Overview

This strategy relies on lowering the probability of highly susceptible species contacting inoculum from residual stumps and roots left after harvest. The technique employed is termed avoidance planting. Seedlings are deliberately planted some distance away from stumps, or in small clumps at minimum or somewhat less than minimum inter-tree spacing. This reduces the chance of root contact occurring too soon after planting, when residual woody debris is still likely to contain inoculum.

When reforesting Armillaria infested sites, trees should be planted at least 50 cm away from stumps. For Phellinus and Tomentosus, highly susceptible tree species should be kept at least 5 m away from infected stumps.

Strategy: biological or chemical agents

Overview

The strategy of employing chemical agents to treat root pathogens is not new. Substances such as chloropicrin are well known as soil fumigants and toxins to various fungi. Unfortunately, they are also lethal to humans. Currently, no chemical is advocated for treatment of root diseases in B.C.

The use of biological agents to treat forest root disease is a relatively recent development. There are three major difficulties with biological control. First, it is difficult to detect, isolate and identify biological agents that are sufficiently antagonistic to specific root pathogens. Second, once discovered, it is often difficult to field test these agents due to the public spectre of biological experiments running amok. Last, field delivery of biological agents to infected sites is often difficult. Currently, no biological agents are available for use against root pathogens in B.C.


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