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Book: Proceedings of the Second International Turfgrass Research Conference
Published by: American Society of Agronomy, Crop Science Society of America



  1.  p. 344-349
    Proceedings of the Second International Turfgrass Research Conference

    Eliot C. Roberts (ed.)

    ISBN: 978-0-89118-573-4


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Fungicide tolerance - a rapidly emerging problem in turfgrass disease control1

  1. H. Cole Jr.,
  2. C. G. Warren and
  3. P. L. Sanders


Isolates of Sclerotinia homoeocarpa from benomyl control failure locations were compared with isolates from nonproblem turf grass areas in terms of culture plate morphology and greenhouse disease symptom development. Fungicide tolerance was evaluated for 54 isolates in fungicide-amended acid potato dextrose sugar (PDA). Growth inhibition was determined for benomyl, Thiabendazole, thioallophanate-ethyl and methyl, and Bay Dam 18654. Isolates from control failure locations grown on fungicide-amended PDA were over 100 times as tolerant to benomyl as isolates from other areas. Tolerance to benomyl was associated with tolerance to other benzimidazole configuration fungicides.

Selected tolerant and nontolerant isolates were used as inoculum in greenhouse fungicide experiments on turf grass. The results indicated that isolates from control failure locations were comparable in all respects except tolerance to nontolerant isolates of S. homoeocarpa. Disease symptoms on creeping bentgrass (Agrostis palustris Huds. cv ‘Penncross’) following inoculation with benomyl-tolerant isolates were well within the range of symptoms expressed following inoculation with benomyl-sensitive isolates.

In greenhouse fungicide experiments with creeping bentgrass benomyl or Bay Dam 18654 provided no control of tolerant isolates. With the tolerant isolate S-50, benomyl spraying resulted in more severe disease symptoms than the unsprayed check plants. Actidione and Dyrene were equally effective in controlling both tolerant and nontolerant isolates. Additional index words: Agrostis palustris.

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Copyright © 1974. Copyright 1974 by the American Society of Agronomy, Inc. and the Crop Science Society of America, Inc., 5585 Guilford Rd., Madison, WI 53711 USA