J.B. Frie, R.K. Zollinger, F.A. Manthey, and B.R. Durgan
1994 NCWSS Proceedings, Vol. 49
Abstract. Wild oat (Avena fatua) resistance to diclofop was first reported in the Red River Valley of eastern North Dakota and western Minnesota in 1992. This area has a high population of wild oat and diclofop is used extensively for wild oat control. The objective of this research was to determine the magnitude and distribution of wild oat resistance to ACCase-inhibiting herbicides. Wild oat was tested for resistance to diclofop, fenoxaprop, quizalofop, fluazifop, clethodim, and sethoxydim in 1994.
Wild oat seed was tested for resistance through a petri plate assay using susceptible and documented ACCase herbicide resistant wild oat seed. The resistant biotype, UM1, was from Canada, and NDS93, a susceptible biotype, was from North Dakota. Parameters such as diclofop and fenoxaprop concentration, seed germination, length and weight of both roots and shoots, and duration of experiment were tested. The petri plate assay included germinated seeds (radicle length or 4 mm) exposed to a concentration of 1.0 ppm fenoxaprop at 20 C, in the dark, for 72 hr. The control consisted of deionized water. Roots were excised after 72 hr of exposure. Root weight in fenoxaprop solution was compared to root weight of the control to determine if the biotype was resistant. If root weight was greater than or equal to 50% of the control, the biotype was considered resistant. Those weighing less than 50% of the control were considered susceptible.
One hundred and forty six locations were tested; 45 locations had at least one plant that expressed resistance to diclofop and fenoxaprop. Seed from 45 resistant locations were planted in the greenhouse and treated with diclofop, fenoxaprop, quizalofop, fluazifop, clethodim, and sethoxydim to determine if biotpyes resistant to diclofop and fenoxaprop were resistant to other related herbicides and to document accuracy of the petri plate test. Seventy three percent of the plants resistant to diclofop in the petri plate were resistant to diclofop in the greenhouse, 24% to fenoxaprop, 16% to quizalofop, 7% to fluazifop, and none to clethodim or sethoxydim. This suggests that the developed petri plate assay is approximately 73% accurate when allowing for a type I error. Twenty seven percent of the plants that were susceptible were labeled resistant (type I error). The error of labeling a resistant plant susceptible (type II error) was avoided using this method. Wild oat biotypes at four locations were documented as resistant to diclofop, fenoxaprop, and quizalofop at four locations. Wild oat at one location was documented as being resistant to diclofop, fenoxaprop, quizalofop, and fluazifop. Resistance to sethoxydim or clethodim was not documented at any location. (Published with the approval of the North Dakota Agricultural Experiment Station).