|Juzwik, J. - US FOREST SERVICE|
|Gust, K - UNIVERSITY OF MINNESOTA|
Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 6, 1998
Publication Date: N/A
Interpretive Summary: A 1992 survey indicated that 80 percent of US forest nursery managers use methyl bromide for pre plant fumigation. However, methyl bromide manufacture and use will cease in the US after 1 Jan 2001, because it is a greenhouse gas contributing to global climate change. A field evaluation scheme tested in 3 bareroot tree nurseries indicated plant (root rot) pathogen inoculum and actual root rot was somewhat controlled by cultural practices including tillage systems and burial of residue produced by cover crops. Cover crops are purposely grown to maintain soil structure produced by actively decomposing organic matter. One of the nurseries successfully produced bareroot transplants without fumigation. More tests are needed to test generic use of this scheme in a variety of nursery conditions including other plants, climate, soils, and pests. This information should be useful in a generic sense for nursery management, where dependance upon fumigation can be the last resort and alternative fumigants to methyl bromide can be used successfully.
Technical Abstract: Conifer seedlings in bareroot nurseries are frequently damaged and destroyed by soil-borne pathogenic fungi, which cause root rot. Nursery cultural practices, soil characteristics, and populations of pathogens in the soil were examined in 3 bareroot tree nurseries in Midwestern USA. Soil-borne populations of Fusarium spp. and Pythium spp. were enumerated, as a function of soil depth in the upper 42 cm; root rot was examined in root systems of red and white pine seedlings. Soil organic carbon (SOC) and cone index (CI), as a function of depth were augmented by saturated hydraulic conductivity (Ksat), water retention characteristic, texture and pH at selected depths. CI provided accurate "fingerprints" of cultural practices in each nursery. A tillage pan due to rotary tillage was detected by CI in the MN and WI nurseries, but no such tillage pan was indicated in the MI nursery, which has not used rotary tillage. CI curves also indicated ddiffering maximum depth of tillage disturbance between nurseries; maximum rooting depth based on 3 MPa CI were different among nurseries. Vertical distribution of soil-borne Fusarium spp. correlated with SOC, which suggested that cover-crop incorporation and conifer rooting repeated over the years had determined the location of soil-borne Fusarium spp. propagules. Ksat suggest that tillage pans caused by rotary tillage may impede drainage, during nearly daily irrigation, enough to cause physio- logical stress to the seedlings and predispose them to disease. Tillage should be used to control depth placement of biomass residue and pathogenic fungal propagules, and adjusted to prevent tillage pans within the seedling root zone. Studies are needed to determine the generic impact of these cultural controls on the need and type of fumigation for pathogen control.