EFFICACY OF BIOCONTROL AGENTS APPLIED TO BARE-ROOT CONIFER SEEDLINGS GROWN UNDER MINIMAL BUFFER ZONE RATES OF SOIL FUMIGATION
Horticultural Crops Research
2012 Annual Report
1a.Objectives (from AD-416):
(1) Assess the efficacy of applied multiple biocontrol agents (e.g., Bacillus subtilis, Streptomyces lydicus, Gliocladium virens, and Trichoderma harzianum) to augment control of root pathogenic fungi (Fusarium, Pythium and Cylindrocarpon) in seedlings growing in soils treated with low levels of chemical fumigants (25-foot buffer rates using TIF tarps); (2) Apply PCR-based techniques to soil and seedling samples to assess Cylindrocarpon spp. present in PNW nurseries; (3) Quantify efficacy of various fumigants combinations on buried Cylindrocarpon inoculums; (4) Assess the economic viability of each treatment; and (5) Conduct educational outreach to project stakeholders
1b.Approach (from AD-416):
Four fumigant treatments (including an untreated control) will be applied at two forest nurseries according to a randomized complete block design with four blocks. Four biocontrol treatments (including an untreated control) will then be applied within each fumigant-treated plot for a total of sixteen treatments. Douglas-fir seedlings will be planted into each fumigant × biocontrol treatment plot and assessed for growth. Soil will be assayed by standard dilution plate procedures for the presence of Cylindrocarpon, Fusarium, and Pythium species before and after the application of fumigant and biocontrol treatments, and at the termination of the experiment. Weed populations will be quantified within each broader fumigation plot after Douglas-fir seedlings have been planted.
The field component of this experiment was completed in May 2012, and data analyses are underway. Preliminary results indicate that the three biocontrol treatments applied to Douglas-fir seedlings were ineffective in controlling root rot caused by Pythium, Fusarium, and Cylindrocladium species. However, the two reduced-rate alternative fumigant treatments were as effective as methyl bromide in controlling root rot. The results are significant because the alternative fumigant treatments will allow growers to continue to manage soilborne diseases in forest nurseries as methyl bromide use is phased out. This research was conducted in support of objective 308 1A: Development of New Technologies for Alternatives and Integration into Commercial Crop Production Systems Currently Dependent upon Methyl Bromide Soil Fumigation.