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

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.

Ground-penetrating Radar to Detect and Quantify Residual Root Fragments Following Peach Orchard Clearing

“…In the GPR survey of the commercial replant orchard, the predicted residual root biomass per plot ranged from 16.6 to 77.5 g•m −3 of soil (Table 3); this could pose a substantial infection threat to newly planted trees, as only 4 g of root inoculum can provide enough inoculum potential for successful infection by Armillaria (Garrett, 1956). To address the practical relevance of residual root inoculum, Roth et al (2000) conducted a 20-year study using different land-clearing strategies for Armillaria inoculum reduction in a ponderosa pine (Pinus ponderosa) stand. For the land-clearing treatment most akin to that used in peach production (trees pushed over and maximum root removal by machine), the authors reported a residual dry-weight root biomass of more than 14 kg•m −3 of soil, which is almost 20 times higher than the highest biomass inferred in our survey.…”

“…The species A. tabescens and A. mellea can cause extensive tree mortality in peach orchards in the southeastern U.S. (Miller, 1994;Rhoads, 1954;Savage et al, 1953), a problem that is becoming more prevalent as producers are forced to plant into forest lands or old orchard sites with endemic populations of these fungi. Armillaria populations are capable of surviving for decades on infested root pieces that remain in the soil after tree removal (Reaves et al, 1993;Roth et al, 2000), and contact between growing roots of replanted trees and infested residual root pieces in the soil is thought to initiate the disease (Rishbeth, 1964;Savage et al, 1953). Residual roots with diameters as small as 0.7 cm can support survival of Armillaria, whereas those of larger diameters are more important for establishing infection based on their greater inoculum potential (Bliss, 1951;Chandler and Daniel, 1982;Patton and Riker, 1959).…”

Armillaria species on small woody plants, small woody debris, and root fragments in red pine stands

“…Some treatments may reduce the overall amount of primary inoculum on a site, but may fragment and redistribute residual inoculum (Bruhn et al 1996(Bruhn et al , 1998Morrison et al 1988). While volume rather than numbers of substrate units may become more important with time after planting (Morrison et al 1988), Roth et al (2000) suggested that in the short term, for example, the decade following site treatment, numbers, rather than size, of inoculum pieces are better indicators of the likelihood of infection. For seed orchards, Bruhn et al (1996) suggest ranking potential sites based on the amount of woody residual present which could support root disease, rather than ranking based on current inoculum levels.…”

“…In conifer orchards in Ontario treated to remove residual roots and debris, the median-sized pieces of debris in the root zones of trees killed by A. ostoyae from sites that were fallow before planting for 1 and 5 years were 2 and 7 cm 3 , respectively (Bruhn et al 1998). Roth et al (2000) reported that 20 years after ponderosa pine had been regenerated on infected sites, the only sanitation treatment consistently associated with reduced mortality from armillaria root disease was hand removal of roots following mechanical push-out logging.…”

“…This information would be useful in choosing methods for root disease management, and especially sanitation procedures. These procedures are expensive, may cause excessive disturbance to a site, and may leave varying amounts of residual inoculum to contribute to root disease (Hagle and Shaw 1991;Reaves et al 1993;Bruhn et al 1998;Roth et al 2000;Sturrock 2000;Omdal et al 2001).…”