Abstract: Dicamba is a herbicide used for the control of broadleaf weeds in wheat. Dicamba, applied within the recommended growth stage interval, reduced the grain yield of Wakefield winter wheat by 95% in a herbicide sensitivity study at Michigan State University. Growers have also reported yield loss when using dicamba on Wakefield. Field and greenhouse experiments were conducted to characterize the response of Wakefield winter wheat to dicamba and to compare this response to that of ‘Harus’ winter wheat, a cultivar that is not considered sensitive to dicamba. This research was conducted to characterize the sensitivity of Wakefield to dicamba and to develop visual methods for detecting sensitivity of wheat cultivars to dicamba. Field experiments confirmed that dicamba affects the number of spikelets and the seed weight of Harus and Wakefield similarly. However, dicamba, applied within the recommended application interval, caused small, shriveled (underdeveloped) seeds to occur in Wakefield in the field and greenhouse. These seeds weighed very little, did not contribute to grain yield, and could not be harvested mechanically. Dicamba reduced the number of fully developed seeds of Wakefield by as much as 62% in the field and 92% in the greenhouse when applied within the recommended application interval. The number of fully developed seeds of Harus was reduced in the field only when dicamba was applied later than the recommended application interval. Decreases in grain yield due to dicamba were caused primarily by decreases in the number of fully developed seeds. Greenhouse experiments indicated that pollen abnormalities were only a minor cause of the development of underdeveloped seeds.

Nomenclature: Dicamba; winter wheat, Triticum aestivum L. ‘Harus’, ‘Wakefield’.

Additional index words: Herbicide sensitivity, growth regulators.

Abbreviations: F2, Feekes stage 2; F3, Feekes stage 3; F5, Feekes stage 5; F9, Feekes stage 9; F10, Feekes stage 10.