Inoculum Reduction Measures to Control Armillaria Root Disease in a Severely Infested Stand of Ponderosa Pine in South-Central Washington: 20 Year Results

Abstract

Abstract A stand of ponderosa pine (Pinus ponderosa) severely impacted by Armillaria root disease was treated with five different levels of sanitation by root removal in an attempt to reduce losses to root disease in the regenerating stand. Treatments included: (1) Trees pushed out, maximum removal of roots by machine, visible remaining roots picked out by hand; (2) Trees pushed out, maximum removal of roots by machine; (3) Trees pushed out, no further removal of roots; (4) Trees pushed out, large stumps left, otherwise maximum removal of roots by machine; (5) Clear logged, sod scalped between the stumps, stumps retained. After 20 yr there was a general reduction in mortality with improved sanitation, although treatment #3 was less effective than expected. In each type of stand regeneration (thinned, unthinned, and planted), only treatment #1 consistently expressed less mortality than the other treatments, and differences were significant in the thinned and unthinned portions of the experiment between treatments #1 and #5. Crop tree height and diameter growth after 20 yr were also best in treatment #1. These results do not necessarily indicate that push-over logging is ineffective, but rather they show that after trees and intact stumps have been pushed out, further cleaning is needed to reach the satisfactory sanitation level achieved in treatment #1. Hand cleaning as done in treatment #1 would certainly be cost prohibitive, but perhaps that level of root removal could be achieved in light textured soils with judicious use of a land-clearing brush rake. West. J. Appl. For. 15(2):92-100.