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Evaluation of Trichoderma harzianum-Impregnated Clay Granules as a Biocontrol for Phytophthora cinnamomi Causing Damping-Off of Pine Seedlings. W. D. Kelley, Assistant Professor, Department of Botany and Microbiology, Auburn University Agricultural Experiment Station, Auburn, Alabama 36830; Phytopathology 66:1023-1027. Accepted for publication 26 December 1975. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1023.

A molasses-amended, Trichoderma harzianum-infested preparation of attapulgus clay granules was tested in the greenhouse as a biocontrol for Phytophthora cinnamomi-induced damping-off of shortleaf pine seedlings. Tests were conducted in flats containing either autoclaved or nonautoclaved soil; flats were watered twice weekly or kept near saturation under a mist system. When incorporated into the soil simultaneously with the P. cinnamomi inoculum, T. harzianum was most effective in reducing disease incidence in flats that received water twice weekly; an additional application of Trichoderma-granules to the soil surface after 2 weeks resulted in a reduced seedling stand, indicating that leaching possibly provided a nutrient source for P. cinnamomi. Seedling survival was poorest in flats in which soil moisture was maintained at near saturation, indicating that T. harzianum could not compete and that the residual nutrients contained in the granules were utilized by P. cinnamomi. Examination of seedlings along demarcation lines between treatments in multi-treatment flats revealed that neither T. harzianum nor P. cinnamomi affected seedling survival in adjacent treatments; thus, growth and/or mobility of each organism beyond its respective inoculated area apparently was restricted. For nonautoclaved soil, evaluation of T. harzianum for control of P. cinnamomi was hindered owing to interactions with other damping-off pathogens. Results indicate that such a preparation of T. harzianum cannot be considered an effective biocontrol agent for P. cinnamomi.

Additional keywords: Pinus echinata, blackstrap molasses.