Effect of Glyphosate Herbicide on Pseudothecia Formation by Pyrenophora tritici-repentis in Infested Wheat Straw. U. Sharma, Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan 66506. E. A. Adee, and W. F. Pfender. Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan 66506. Plant Dis. 73:647-650. Accepted for publication 21 November 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0647.

Field-grown wheat straw infested with Pyrenophora tritici-repentis was treated with several herbicides used in no-tillage wheat production and then incubated under moist conditions in the greenhouse. Formulated herbicides containing bromoxynil, dicamba, glyphosate, 2,4-D, or paraquat, applied at labeled rates, significantly reduced ascocarp production by P. tritici-repentis. The glyphosate-containing herbicide Roundup (Monsanto Agricultural Co., St. Louis, MO) was the most effective; no ascocarps were produced in straw treated with this material. In further experiments with this herbicide, greenhouse-grown straw infested with P. tritici-repentis was treated with it either before incubation under conditions conducive to ascocarp development or at one of several times after incubation had started. The herbicide completely inhibited ascocarp development if applied before the conducive environment was imposed, but this inhibition diminished as the time delay increased between inoculation and treatment. Experiments conducted on autoclaved, inoculated straw indicated that the herbicide does not greatly reduce the mycelial growth rate of P. tritici-repentis. It was not determined whether the effect of the formulated material is due to glyphosate or to the nonherbicidal components of the material.