Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2007
Publication Date: 11/1/2007
Citation: Martinson, K., Durgan, B., Forcella, F., Wiersma, J., Spokas, K.A., Archer, D.W. 2007. An Emergence Model for Wild Oat (Avena fatua). Weed Science. 55:584-591. Interpretive Summary: Wild oat continues to be a troublesome weed throughout wheat-growing areas of the United States and Canada. Timely and more accurate control of wild oat may be possible with better understanding of wild oat seedling emergence patterns. Wild oat seedling emergence patterns were evaluated in northern Minnesota and adjacent North Dakota, and two predictive models were developed using soil growing degree days (GDD) or soil hydrothermal time (HTT). HTT is similar to GDD but includes the effects of soil water stress on seedling emergence. Wild oat emergence always began between May 1 and 15 and continued for up to six weeks. Levels of wild oat emergence were correlated with GDD and HTT, but not calendar days. In other words, the extent of wild oat emergence cannot be estimated based upon the day of year because weather patterns change so much from one year to the next or one location to the next. Instead, seedling emergence was associated more closely with soil GDD and soil HTT, and mathematical equations were developed to describe these effects. These equations represent "models," and they subsequently were tested for accuracy at sites and during years that were not involved in the original development of the models. Both the GDD-based model and the HTT-based model closely fit observed wild oat emergence patterns. The HTT-based model may have wider application because it includes effects of soil water stress on seedling emergence. Nevertheless, both models can aid other researchers in the future study of wild oat seedling ecology, and both also can assist growers and agricultural professionals with planning timely and more accurate control operations for wild oat in wheat and other small grain crops.
Technical Abstract: Wild oat is an economically important annual weed throughout small grain producing regions of the United States and Canada. Timely and more accurate control of wild oat may be developed if there is a better understanding of wild oat emergence patterns. The objectives of this research were to evaluate the emergence pattern of wild oat, and determine if emergence can be predicted using soil growing degree days (GDD) and/or hydrothermal time (HTT). Research plots were established at Crookston, MN, and Fargo, ND, in 2002 and 2003. On a weekly basis, naturally emerging wild oat plants were counted and removed from six 0.37 m2 permanent quadrates randomly distributed in a wild oat infested area. This process was repeated until no additional emergence was observed. Wild oat emergence began between May 1 and 15 at both locations and years and continued for four to six weeks. Base soil temperature and soil water potential were determined to be 1 deg C and -0.6 MPa, respectively. Wild oat emergence was correlated with GDD and HTT but not calendar days (p=0.15). A Weibull function was fitted to cumulative wild oat emergence and GDD and HTT. The models for GDD (n = 22, r2=0.93, RMSE=10.7) and HTT (n= 22, r2=0.92, RMSE=11.2) closely fit observed wild oat emergence patterns. The latter model is the first to use HTT to predict wild oat emergence under field conditions. Both models can aid in the future study of wild oat emergence and assist growers and agricultural professionals with planning timely and more accurate wild oat control.