Submitted to: Phytoparasitica
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/11/2003
Publication Date: 12/11/2003
Citation: Fravel, D. R. Lewis, J. A. 2004. Effect of label and sublabel rates of metam sodium in combination with Trichoderma hamatum, T. harzianum, T. virens, and T. viride on survival and growth of Rhizoctonia solani. Phytoparasitica 32:111-118. Interpretive Summary: The soil-inhabiting fungus Rhizoctonia solani causes damping-off disease in many crops. We determined whether combining beneficial, biocontrol fungi (four species of Trichoderma) with the recommended label rate or reduced rates of a soil fumigant could kill or lessen the activity of the fungus Rhizactonia in soil. Even though biocontrol fungi were added before the fumigant, combining the biocontrol fungi with the label rate of the fumigant further reduced viability and soil activity of Rhizoctonia. While combining the biocontrol fungi with diluted fumigant initially decreased growth of Rhizoctonia, only Trichoderma harzianum combined with the fumigant reduced growth of the pathogen for the entire test period. This information will be used by scientists developing integrated management strategies for control of damping-off.
Technical Abstract: This work was undertaken to determine the effects of Trichoderma spp. combined with label and sublabel rates of metam sodium on survival and saprophytic activity of Rhizoctonia solani in soil. To study survival, sterile beet seed were colonized with R. solani and used to infest soil. Soils were also infested with wheat bran preparations of Trichoderma hamatum Tri-4, T. harzianum Th-58, T. virens Gl-3, and T. viride Ts-1-R3. Soils were then treated with water (control) or with metam sodium at a rate equivalent to 935 l/ha and 1:10, 1:50, 1:100, 1:1000 dilutions of this. The 935 l/ha rate was considered equivalent to the label rate for most crops. Beet seed were later recovered and plated onto water agar plus antibiotics. Growth rate of R. solani from the beet seed was recorded. There were no interactions (P > 0.35) between any biocontrol agent and the fumigant with respect to either survival or saprophytic activity, reflecting that all Trichoderma isolates tested reacted similarly to increasing concentrations of metam sodium. At the label rate of metam sodium, all Trichoderma spp. significantly reduced the growth of R. solani from beet seed over the 4 day period during which R. solani growing from nontreated beet seed grew to the margins of a 9 cm petri plate. When the fumigant was used at the 1:10 or 1:50 rate, all Trichoderma spp. initially reduced the growth of R. solani from beet seed compared to the control. Only T. harzianum combined with the 1:10 dilution of the fumigant significantly reduced the rate of growth during the whole test period. There were no differences in growth between the control treatment and the biocontrol treatments when the fumigant was added at the 1:100 or 1:100 rate. Combining T. hamatum or T. virens with a 1:50 or 1:100 dilution of metam sodium significantly reduced the saprophytic activity of R. solani. The reduced growth rate of R. solani indicates that survived reduced rates of the fumigant indicates that R. solani was weakened and thus possibly more susceptible to attack by the biocontrol fungi.