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Title:   Author  item
                                            KLITH JENSEN, RIKKE - DANISH INST. AGRIC SCI.item
                                            Archer, Daviditem
                                            Forcella, Frank
  Submitted to: Plant Protection Conference Proceedings
                                    Publication Type: Proceedings
                                    Publication Acceptance Date: 2/1/2002
                                    Publication  Date: 2/1/2002
                                    Citation: KLITH JENSEN, R., ARCHER, D.W., FORCELLA, F. MODELING SHOOT EMERGENCE OF CANADA THISTLE BASED ON DAY DEGREES. DJF RAPPORT. 2002. V. 64. P. 129-135.Interpretive Summary:
                                Technical Abstract: One of the most serious weeds in northern temperate agricultural environments is Canada thistle. The timing of shoot emergence of weeds represents important information that enables managers to implement control operations at critical times. Shoot emergence from adventitious root buds of Canada thistle in Denmark and North Dakota (USA) was studied and compared to thermal time (growing degree days) in order to develop a predictive model. The heat sum was accumulated from seedbed preparation, and it was found that a Weibull function gave a better fit than a logistic function, especially at the lower emergence levels. Further, a Weibull function based on cumulative soil thermal time with a base temperature of 0°C explained more variation (r**2=0.96) than the same model using accumulated air temperature. It was found that 80% shoot emergence was obtained at a heat sum of 350 degree-days. Because the original data spanned years and continents, the resulting model may be sufficiently robust to  have widespread utility predicting shoot emergence of Canada thistle.


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