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Title: Modeling the Emergence of Three Arable Bedstraw (Galium) Species

item ROYO-ESNAL, ARITZ - Universitat De Lleida
item TORRA, J - Universitat De Lleida
item CONESA, J - Universitat De Lleida
item Forcella, Frank
item RECASENS, J0RGE - Universitat De Lleida

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2009
Publication Date: 1/1/2010
Citation: Royo-Esnal, A., Torra, J., Conesa, J.A., Forcella, F., Recasens, J. 2010. Modeling the Emergence of Three Arable Bedstraw (Galium) Species. Weed Science. 58:10-15.

Interpretive Summary: Bedstraws or cleavers are serious weeds in small grain crops throughout the temperate parts of the world. They can germinate and emerge in autumn or in spring to plague both winter- and spring-growing cereals. Understanding the emergence patterns of their seedlings was one goal of this joint research project between Spanish and ARS researchers. The other goal was to develop predictive tools to simulate emergence. These tools are in the form of computer models that use growing degree days (GDD) to make emergence predictions. GDD are calculated based on either of two criteria: (a) local daily soil temperatures or (b) local daily soil temperatures as modified by daily soil moisture status. In the latter case GDD are accumulated only when the soil is wet, but not when it is too dry to support seed germination. This approach was used for three species of bedstraw: catchweed bedstraw, threehorn bedstraw, and false cleavers. Original field data from wheat fields in Spain were used to develop the mathematical models, and independent field data from England were used to test the validity of the model for catchweed bedstraw. All of the models appeared to simulate the original data well, which was expected. Moreover, the model for catchweed bedstraw, the most common species, also closely mimicked the independent results from England, which indicated that these models likely can be applied beyond northeastern Spain where the original data were collected. Although these models, like all computer models, must be thoroughly examined in other locations to be certain of their accuracy, they appear useful for helping extension educators, crop advisors, agrichemical industry personnel, and growers make timely management recommendations and decisions based upon when bedstraws are emerging in field soils.

Technical Abstract: Seedling emergence was modelled for three arable species of bedstraw (Galium), which may coexist in winter cereal fields, using multi-year field data from Spain. The relationships between cumulative emergence and both growing degree days (GDD) and hydrothermal time (HTT) in soil were analyzed as sigmoidal growth models (Weibull), and iteration of base temperature and base water potential was used to optimize the HTT scale. All species were fitted significantly to Weibull models. G. aparine showed good fit to both GDD and HTT, as its seedlings have less dependence on soil water potential than G. spurium and G. tricornutum, which were fitted best with HTT. The latter species exhibited higher requirements for soil water to emerge, and its model was validated successfully with independent data from the United Kingdom. The models may be useful for predicting bedstraw emergence in semiarid Mediterranean regions and elsewhere.