Annosum root rot affects conifers throughout the Northern Hemisphere, leading to root rot, windthrow, and ultimately, the death of infected trees.
The fungus Heterobasidion annosum causes annosum root rot. The fungus colonizes readily on freshly cut stumps. Partially cut stands have a high risk of infestation because the fungus can colonize on each of the stumps, potentially leading to the loss of many residual trees.
Wind and rain carry the annosum spores. Spores that land on freshly cut stumpsgrow down the stump's root system, where they can infect living trees through root grafts or root contacts.
Once annosum becomes established, it can remain active for many years in the South and for several decades in the North. In the South, the hazard rating for annosum root rot is based on soil type. We conducted our preliminary tests at the Department of Energy's Savannah River Site in South Carolina. Stands of conifers on sandy, well-drained soils there are classified as high hazard.
The primary method of controlling annosum in partially cut stands is by applying Sporax to the stump immediately after cutting. Sporax is a commercial powdered formulation of borax. Its primary active ingredient is boron. USDA Forest Service engineers have devised an applicator system that attaches to a feller-buncher, allowing the operator to treat the stump immediately after the tree has been cut.
The applicator uses an air compressor located behind the feller-buncher's cab. A hopper holds the Sporax. A mechanism in the hopper controls the amount of powder being applied. Compressed air delivers the Sporax powder to a nozzle behind the cutting head.
Figure 1. Sporax treatment of a stump
Figure 2. Sporax nozzle location
Figure 3Feller-Buncher in operation
The modular design allows timber purchasers to adapt the applicator to virtually any feller-buncher. During timber harvest, the operator cuts the tree, positions the nozzle of the applicator over the stump and activates the system, applying Sporax to the tree stump.
Results
The system was tested in September 1997 on a 9-acre tract and again in May 1998 on a 29-acre tract. After treatment with borax, stumps retained enough boron to prevent annosum root rot.
Total additional cost for treatment $13.36 per acre
Material cost of Sporax (borax) plus 0.5 % Methylene Blue dye. $8.00 per acre
($0.16 per stump with approximately 50 trees per acre removed.) Each pound of borax treated 10.5 stumps.
Additional treatment time and applicator attachment depreciation. $5.36 per acre
Treatment required an additional 6 seconds per tree (3.1 seconds for treatment plus 2.65 seconds on average to keep the borax reservoir filled). The cost of the feller-buncher (includes typical downtime) and operator was estimated at $61.02 per productive machine hour (PMH). The cost of the feller-buncher without treatment on 50 acres per acre removal was $10.34 per acre compared to $15.70 per acre with treatment.
Depreciating 100% of the $3500 cost of the attachments over 3 years (including repair and maintenance) adds $1.94 per PMH to the machine cost.
This publication reports research involving pesticides. It does not contain recommendations for their use, nor does it imply that the uses discussed here have been registered. All uses of pesticides must be registered by appropriate State and/or Federal agencies before they can be recommended.
CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish or other wildlife - if the are not handled or applied properly. Use all pesticides selectively and carefully. Follow recommended practices for disposal of surplus pesticides and pesticide containers.
Figure 4. Schematic of sporax applicator and components
