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Formulation of a Soil Amendment to Control Damping-off of Slash Pine Seedlings. J. W. Huang, Former graduate student, Department of Plant Pathology, University of Georgia, Present address: Department of Plant Pathology, National Chung-Hsing University, Taichung, Taiwan, Republic of China; E. G. Kuhlman, Principal plant pathologist, U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment Station, Carlton Street, Athens, GA 30602. Phytopathology 81:163-170. Accepted for publication 2 August 1990. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1991. DOI: 10.1094/Phyto-81-163.

Seventeen chemical amendments were added (1%, w/w) individually to sandy soil artificially infested with Rhizoctonia solani (AG-4) or a binucleate species of Rhizoctonia (CAG-3). Alum, Al2(SO4)3, CaCl2, Ca(NO3)2, CaO, glycerine, K2HPO4, KCl, K2SO4, NH4NO3, (NH4)2SO4, urea, and triple superphosphate inhibited colonization of pine stem segments by R. solani and the binucleate Rhizoctonia to varied degrees. In 0.1% (w/v) water solution, these chemicals inhibited sporulation of Pythium aphanidermatum. Ammonium sulfate suppressed the incidence of damping-off by 2035% as compared with other N-fertilizers; ammonium nitrate enhanced damping-off by R. solani. A growth medium of 100% milled pine bark almost completely controlled damping-off by Pythium and reduced damping-off caused by R. solani by 50%, but it did not protect seedlings from infection by the binucleate Rhizoctonia. A soil amendment (SF-21) was formulated from 750 g of milled pine bark, 35 g of (NH4)2SO4, 10 g of triple superphosphate, 30 g of CaC12, 25 g of KCl, 150 g of A12(SO4)3, and 750 ml of 10% glycerine. Added at 1% (w/w) to soil, SF-21 controlled more than 50% of damping-off of slash pine seedlings caused by P. aphanidermatum, R. solani, and binucleate Rhizoctonia in fumigated or nonfumigated soils in the greenhouse. In fumigated and nonfumigated soils in field microplots with or without a damping-off pathogen and amended at the rate of 2,400 kg/ha before sowing slash pine seeds, SF-21 significantly reduced post-emergence damping-off caused by R. solani, P. aphanidermatum, and Fusarium moniliforme var. subglutinans by 3638, 2528, and 1222%, respectively, in two tests. When added after the first appearance of damping-off, the SF-21 mixture also reduced losses to those fungi, with the exception of F. m. subglutinans in the first test. SF-21 treatments also increased the number of healthy seedlings produced per unit of area and the height of slash pine seedlings. Populations of R. solani and P. aphanidermatum were reduced by 5090% 4 wk after treatment of the microplots. In soil amended with SF-21, the predominant fungi, Trichoderma harzianum, T. aureoviride, Penicillium oxalicum, P. funiculosum, Gliocladium deliquescens, and G. fimbriatum were stimulated, and the colony-forming units increased from 0.9 105 to 3.8 106/g of dry soil and remained high for more than 50 days.

Additional keywords: biocontrol, pine bark mulch.